How long until the Earth and Moon become a binary planet?

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With the rate at which the moon is further receding into a higher orbit, how long until the barycentre between us and the moon leaves the earth, and going by the IAUs 2006 definition update, we become a double planet?

I'm not sure I agree with the double planet POV, but the calculation is pretty simple. The earth weighs 81 moons, so for the Barycenter to be outside the earth, the distance (center of Moon to surface of earth), = 81 earth radii.

or about 515,000 KM. It's current farthest distance is 405,000 KM, average distance 384,000 KM and closest 363,000 KM Source, so, it depends on whether you mean, temporarily outside, outside more than 50% of the time or always outside - each would provide different answers.

But moving away 4 CM per year (same source) or 1 KM every 25,000 years, it would need 2.75 billion years to move away the necessary 110,000 KM necessary to have the barycenter move outside of earth at the moon's furthest point. (less if the orbit gains eccentricity which is possible). But probably more than that, cause as the moon moves away from the earth, the tidal forces that continue to push it away grow weaker and the earth slows down a little. If the earth ever gets tidally locked with the moon, the reverse will happen and the sun's tidal forces will draw the Earth and Moon slowly towards each other, so a precise answer is too mathematically difficult for me, but longer than 2.75 billion years seems a pretty good guestimate.

Radio waves from famous FRB surprisingly long and late

In this illustration, a burst of radio emission from a repeating fast radio burst arrives at the LOFAR telescope. The longest-wavelength part of the signal (red) is far longer than has ever been seen before from a fast radio burst. Plus, the longer-wavelength emission is arriving about 3 days later than the shorter-wavelength (higher-frequency, shown in purple) part of the emission. The inset is an image of the host galaxy of this fast radio burst, similar to our home galaxy, the Milky Way, but 500 million light-years away. Image via D. Futselaar/ S.P. Tendulkar/ ASTRON.

It was just over a decade ago that astronomers noticed bursts of radio waves from the cosmos, lasting just milliseconds, now known as fast radio bursts (FRBs). Today, these bursts are still shrouded in mystery, as astronomers work to gather clues to their nature. This month (April 2021), an international team of astronomers announced it has now broken an observational record for FRBs, by measuring radio bursts from one of the best-studied FRBs – known as FRB 20180916B – at lower frequencies (longer wavelengths) than ever before. They also found this very low frequency signal from FRB 20180916B arrives three days after higher frequency emission from the same object. This strange discovery provides new and important information about the enigmatic origin of FRBs.

The research was published in the peer-reviewed Astrophysical Journal Letters on April 9.

The paper’s lead author Ziggy Pleunis, a postdoctoral researcher at McGill University in Montreal, Canada, explained:

We detected fast radio bursts down to 110 MHz, where before these bursts were only known to exist down to 300 MHz. This tells us that the region around the source of the bursts must be transparent to low-frequency emission, whereas some theories suggested that all low-frequency emission would be absorbed right away and could never be detected.

The team studied a repeating FRB, known as FRB 20180916B, that was discovered in 2018. It is located in the outskirts of a galaxy similar to our Milky Way galaxy, at a distance of about 500 million light-years. Because this is considered close in astronomical measures and because the burst is repeating, the FRB has been the focus of several studies, revealing, for example, that is has a 16.3 day periodicity in its activity, meaning it sends out a new burst every 16 days. This made it the first predictable radio burst.

Pleunis told EarthSky that there are two prevailing explanations for the 16-days-between-bursts timing:

One possibility is that the FRB source is in a binary (double) system, and the FRBs only become observable from Earth for a few days once every orbital rotation. The rest of the time the emission is pointed away from us or obscured. The other possibility is that the FRB source is precessing [its magnetic pole is changing direction], and the FRBs only become observable from Earth for a few days once every precession period when the emission is pointed towards us.

Those explanations might explain the 16-days-between-bursts timing. But the new research also found that the emission from the FRB arrives at different times, depending on frequency (that is, in a manner directly related to how long the waves of the signal are). The team discovered that the newly observed low-frequency radio emission consistently arrived three days later than that of the higher frequencies.

Ziggy Pleunis at McGill University is the lead researcher of a new study that found fast radio burst signals at longer wavelengths than ever before, arriving 3 days later than their shorter wavelength counterparts. Image via Z. Pleunis.

How can that be? All electromagnetic emission travels at the same speed, the speed of light (186,000 miles per second, or 300,000 km per second). What would make the lower-frequency signal arrive so late? Pleunis explained to EarthSky these astronomers’ theory for the three-day delay:

In a lot of models, FRBs are produced in the magnetic field surrounding a neutron star [a highly compact star], in a beam or cone emanating from the magnetic poles of the star. It is thought that emission produced at different altitudes in this magnetic field – closer to or farther from the body of the neutron star itself – has different characteristic frequencies because of the changing conditions of the magnetic field. The higher-frequency radio waves would be produced at lower altitudes [closer to the neutron star] than the lower-frequency radio waves.

If there is indeed this kind of relationship between the distance from the star where the burst is produced and the frequency of the burst, Pleunis explained, then, due to the movement of the FRB in both of the 16-day burst scenarios, looking from Earth, you would first face the regions closer to the star before you would “see” the higher altitude regions. This means that you would first measure the emission with the higher frequencies and then, a few days later, you would observe the emission of the lower frequencies.

In other words, the delay in the arrival of the longer-frequency emission might be a consequence of the orientation of the neutron star and its magnetic field (assuming the models are correct that FRBs can be produced in a neutron star’s magnetic field). Pleunis continued:

If a similar FRB source is oriented differently with respect to Earth, it would be possible to see the lower frequency radio waves before the higher frequency radio waves in that system.

If you find all of this hard to visualize, you’re not alone. The inherent movement of the FRB complicates things, for one thing. To make it even more difficult, the magnetic fields are rarely uniform fields with two well-defined beams from each pole (the textbook case). Instead real magnetic fields in nature are a lot more messy.

This schematic illustrates the two possible scenarios for FRB production. In the first scenario (left), a neutron star and another star orbit a common center of mass. In this scenario, you can only see the FRB for a few days from Earth. In the 2nd scenario (right), the neutron star is solitary. Its magnetic pole – the possible source of the FRB signals – is precessing, or changing direction, which makes the FRBs detectable from Earth only for a few days when the emission is pointing toward us. In both scenarios, the burst emission that was formed farther out from the neutron star arrives later than the emission formed closer, which would explain the 3-day delay for the low frequency emission. Image via B. Zhang/ Nature/ Z. Pleunis (annotations). Artist’s concept of the messy magnetic fields surrounding a magnetar, a type of neutron star, believed to have an extremely powerful magnetic field. Magnetars are candidate sources for many fast radio bursts. Image via Carl Knox/ OzGrav.

There are a lot of unknowns regarding FRB progenitors and the emission mechanism … It doesn’t have to be the case that the emission is produced in the beams emanating from the [neutron star’s] magnetic poles, but the emission might also be produced in the magnetic field, as it sizzles and cracks, or it might be produced farther away through the interaction of the neutron star’s magnetic field with, for example, the wind of a companion star.

In other words, this is a very active field of research and there is much yet to learn. Pleunis continued:

Why does the emission have a different characteristic frequency at different altitudes? This would also depend on the as-of-yet unknown emission mechanism for FRBs.

The astronomers used two telescopes, The Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Dutch Low Frequency Array (LOFAR). LOFAR has stations spread out all over Europe to increase the detail of the data. For this project, the astronomers had set the telescope to observe in a range of 110-188 MHz (2.7 to 1.6 meters wavelength).

Because the detections were found at the edge of this range, the astronomers believe they may extend even lower, and are planning to observe at even lower frequencies to learn more.

The following video from JIVE and the EVN describes the repeating FRB 20180916B:

Note that waves of electromagnetic emission – including light – are measured both by the length of the waves (wavelength) and how often they occur (frequency). The longer the wavelength, the lower the frequency and vice versa the shorter the wavelength, the higher the frequency. A good trick to not get confused is to remember the letter L for for the Low frequency/Long wavelength region, which are the waves we are discussing in this article.

Bottom line: Astronomers have measured radio waves from a well-known repeating fast radio burst that are much longer than ever detected before. But not only that, the radio signal also arrived at the telescope a surprising three days after the more energetic part of the same radio burst.

How long until the Earth and Moon become a binary planet? - Astronomy

The International Astronomical Union has just approved an official name for a tiny asteroid satellite set to become the first-ever target of an asteroid deflection mission. The satellite is the smaller of two bodies in the near-Earth asteroid system Didymos, and will now be distinguished from its primary object by the name Dimorphos.

In July 2021, just over a year from now, NASA will launch the Double Asteroid Redirection Test (DART) mission. This first full-scale demonstration of asteroid deflection technology will target the smaller body in the binary asteroid system known as Didymos, and will be followed in 2024 by the ESA space probe Hera. In recognition of the asteroid moon’s significance in these pioneering missions, it has been given an official name: Dimorphos.

Together, the DART and Hera missions, and the international research collaboration known as the Asteroid Impact and Deflection Assessment (AIDA), will demonstrate deflection technology that could be used to protect Earth from hazardous asteroids by shunting them off a collision course. Didymos does not pose a risk of striking Earth, and is the most easily reachable asteroid system of its size, with a primary body about 780 metres in diameter. The smaller body is about 160 metres in diameter — roughly the size of the Great Pyramid in Egypt.

First spotted in 1996 by Joe Montani of the Spacewatch Project at the University of Arizona, the asteroid system’s binary nature was not discovered until 2003, when Petr Pravec of the Ondřejov Observatory in the Czech Republic found the characteristic signs of a binary system in his observations. It was at this point that it received its official name. As the original discoverer, Montani suggested the system be named Didymos, meaning twin in Greek, to reflect its composition, a name which the IAU quickly approved.

While the larger body and the system as a whole have gone by the name Didymos since then, the smaller body has been referred to by many names, including the provisional designation S/2003 (65803) 1 and the nicknames Didymos B and Didymoon, but was never given its own official name. When it was identified as an ideal target for AIDA, the DART and Hera teams decided to seek a permanent designation and an official name by which it could be distinguished from its larger companion.

The body that officially approves the names of minor planets and their satellites is the IAU Working Group Small Body Nomenclature (WGSBN), under the IAU Division F Planetary Systems and Astrobiology [1]. The WGSBN received the proposal to name the satellite Dimorphos, with the following citation: “Dimorphos, Greek for 'having two forms', is the smaller member of the (65803) Didymos system. As the target of the DART and Hera space missions, it will become the first celestial body in cosmic history whose form was substantially changed as a result of human intervention (the DART impact).” The WGSBN accepted the proposal, and the object obtained its final designation as (65803) Didymos I = Dimorphos.

The name of the moon was suggested by Kleomenis Tsiganis, a planetary scientist at the Aristotle University of Thessaloniki and a member of both the DART and Hera teams. He explains that the name Dimorphos “has been chosen in anticipation of its changes. It will be known to us in two very different forms, the one seen by DART before the impact, and the other seen by Hera a few years later.

At present there are 546 077 numbered minor planets, of which 22 129 have official names [2]. The catalogue of minor planets and comets is maintained by the Minor Planet Center (MPC) [3], a service of the IAU. Most of the minor planets belong to the Main Asteroid Belt, in the region between the orbits of Mars and Jupiter. There are 22 735 classified as Near Earth Asteroids (NEA), many of which have orbits that approach the Earth. Didymos belongs to the NEA group. In the minor planet catalogue there are also many examples from the outer regions of the Solar System, objects known as Centaurs and Trans-Neptunian Objects (TNOs). Many minor planets have companions 390 binaries and 15 triple systems have so far been discovered [4]. The binary comprising Didymos and Dimorphos has become the 26th system with approved names for its components. Dimorphos, with a size of 160 metres in diameter, is also one of the smallest objects to get a permanent name.

After its launch next year, DART is scheduled to reach Dimorphos in 2022, deliberately colliding with it and creating a kinetic impact intended to alter the satellite’s trajectory. The ESA space probe Hera will be launched two years later and is scheduled to arrive at Dimorphos in 2027, where it will perform a close-up survey to assess the effects of the DART impact on the satellite’s form and orbit.

The DART impact will be recorded by the LICIACube CubeSat, provided by the Italian Space Agency, which will be carried to Didymos by DART and deployed a few days before the collision. Longer-term effects will be studied by telescopes here on Earth and in space. The Hera mission will also deploy two CubeSats, including the Juventas CubeSat, which will use a low-frequency radar to scan the interior structure of Dimorphos, the first such scan to be performed by a spacecraft. The results of Hera’s detailed investigation will be compared with the observations recorded by DART before the collision, providing important insights into the effects of the impact.

G. Tancredi, president of IAU Div. F and external member of the DART and Hera investigation teams, remarks that: “The IAU has been closely following the development of the research on the Near-Earth Objects and their threat for life on Earth. The IAU Working Group Near Earth Objects (WGNEO) was formed in the early 1990s to coordinate the NEO studies and to provide timely advice on any objects that threaten collision with the Earth.” [5]

Notes

[1] The IAU Division F Planetary Systems and Astrobiology deals with our Solar System, extrasolar planetary systems, and bioastronomy. It has 2370 members distributed all around the world. The President for the Division in the period 2018–2021 is Gonzalo Tancredi. The Division F WG Small Bodies Nomenclature (WGSBN) has responsibility for the naming and designation of small bodies (except satellites of major planets) in the Solar System. It covers the naming of minor planets including Near Earth Asteroids and Trans-Neptunian Objects, comets, dwarf planets and satellites of minor planets. The WGSBN chair in the period 2018–2021 is Jana Tichá and the Vice-Chair is Keith Noll. The Division F WG Near Earth Objects is chaired by Patrick Michel who is one of the leading scientists of the ESA’s Hera mission.

[2] Data taken from the MPC Orbit (MPCORB) Database.

[3] The Minor Planet Center (MPC) operates at the Smithsonian Astrophysical Observatory, under the auspices of Division F of the International Astronomical Union (IAU). The MPC’s operating funds come from a NASA Near-Earth Object Observations programme grant.

[4] Data from the webpage: Asteroids with Satellites, by Wm. Robert Johnston.

[5] The IAU Symposium 374: Astronomical Hazards for Life on Earth will be held during the next IAU General Assembly in Busan in 2021 and will be an opportunity to address this relevant topic for the future of humanity.

More information

The IAU is the international astronomical organisation that brings together more than 14 000 professional astronomers from more than 100 countries worldwide. Its mission is to promote and safeguard astronomy in all its aspects, including research, communication, education and development, through international cooperation. The IAU also serves as the internationally recognised authority for assigning designations to celestial bodies and the surface features on them. Founded in 1919, the IAU is the world's largest professional body for astronomers.

Terrestrial Planet Formation in Binary Star Systems

The list of confirmed extrasolar planets keeps growing, and has now passed two hundred members — almost all of which are gas giants like Jupiter and Saturn. But the hunt is on for Earth-like worlds! With the successful launch of France's CoRoT satellite (December 27, 2006) and the promise of NASA's Kepler mission (due to be launched October 2008), the next five years should see the detection of numerous terrestrial planets around distant stars. But which stars should these telescopes be pointed at? Recent research has shown that these planets are probably quite common, and can even form in binary star systems.

Scientific interest in the physics of planet formation is at an all-time high. Astronomers and physicists have reached a consensus on the underlying theory, or at least its outlines. A star is born from an immense cloud of gas and dust, which slowly contracts and heats up through the action of gravity. Some of the cloud falls towards the center, where it collects into a hot, dense ball of gas that will eventually become the star. The rest of the cloud orbits the center, contracting and flattening into a protoplanetary disk.

Tiny grains of rock and ice stick to each other as they orbit within the disk, eventually growing into 'planetesimals' — small lumps of rock and ice similar to asteroids and comets. At this point gravity speeds up the process of planet formation considerably. Rocky planets form close to the newborn star, where the radiant heat prevents ice from forming. Icy planets form in the cold outer regions, but are much larger to begin with and quickly transform into gas giants.

Each circle in these plots represents a single simulated planet. The horizontal axis gives the radius of its orbit in astronomical units (AU the Earth’s distance from the Sun), and the vertical axis gives the eccentricity of the orbit (zero is a perfect circle). The filled green circles represent our own rocky planets: Mercury, Venus, Earth, and Mars. The grey band indicates the solar system´s habitable zone. The lower plot shows planets from simulations where the point of closest approach between the stars is 10 AU (approximately equal to Saturn’s distance from the Sun). The inner disk has not been compromised many planets form in and around the habitable zone. In the upper plot the companion star cuts this distance in half, and planet formation in the habitable zone is no longer likely.

It is now thought that almost all stars are born with a protoplanetary disk — the question is under what circumstances these disks form useful planets rather than a mass of rubble. The method of choice is numerical simulations, which can follow the evolution of a disk by modeling its gas dynamics (in the early stages of planet formation) or the gravitational interactions between planetesimals (in the later stages). Such research has shown that planets should almost always form, at least around an isolated star like our Sun.

Of course, star formation is a more complicated business.

Stars rarely, if ever, form in isolation. More often, a giant molecular cloud will create dozens or hundreds of stars in relatively close proximity. Binary star systems, composed of two stars orbiting their mutual center of gravity, are actually just as common as singles. For stars the size of our Sun, about 50% form in binary systems.

In the search for other worlds like our own, should we limit ourselves to stars like our own? Must we cut the field in half before we start looking? Might binary stars harbor Earth-like planets as well?

The answer, of course, is that it depends on the system. In principle, stable orbits should be possible for planets that are always much closer to one star than the other. But the devil is in the details — if scientists are going to spend valuable telescope time on binary stars, they need to know what they're looking for. How close can two stars be to each other and still form planets? And even if planets form, can their orbits remain stable over billions of years?

A small collaboration of scientists at NASA’s Ames Research Center (Elisa Quintana, Jack Lissauer), University of Michigan (Fred Adams), and the Carnegie Institution of Washington (John Chambers) has taken steps to answer these questions. Modern telescopes can measure the orbital parameters of binary stars quite accurately, so it makes sense to first ask what kinds of star systems will preserve the innermost region of the protoplanetary disk.

The simulations of Quintana and her colleagues are fairly straightforward. After choosing the masses and orbital parameters of the two stars, 140 planetesimals (mass = 1% Mearth) and planetary embryos (mass = 10% Mearth) are arranged around one of the stars so that their overall mass distribution resembles that of a protoplanetary disk. "The disk is modeled after the Solar nebula," Quintana explains, "we’re comparing the planet formation process in these binaries to models of the Solar System." In other words, they are trying to find out what our Solar system might have looked like if the Sun were a binary star.

The simulation calculates the force of gravity between every pair of objects and adjusts their positions accordingly at one-week intervals. When two objects collide, if their speeds are not too high, they stick together into a body of greater mass. Eventually, the system forms a handful of stable, massive planets similar to the inner solar system.

"Each simulation takes approximately 3 - 4 weeks." Quintana tells PhysOrg.com. "This corresponds to 100 - 200 million years of simulated time." Dr. Quintana goes on the explain that this is actually rather short, because many planetesimals are thrown out of the disk or into the central star as the simulation progresses. "The same disk of 154 bodies around the Sun, without any giant planets or a stellar companion [to eject particles], takes twice as long."

To explore a wide variety of possible binary star systems and obtain statistically significant results, Quintana and her colleagues performed over a hundred of these simulations — that's several years of computer time!

All of their simulations form at least one planet, an encouraging result. It turns out that the most important factor is the companion star's periastron, or point of closest approach to the star with the disk. A companion that gets as close as the orbit of Saturn (about 10 times farther than the Earth from the Sun) removes very little material from the inner disk, and even speeds up the process of planet formation by nudging the planetesimals into different orbits from time to time. A companion star that gets as close as Jupiter (about 5 times farther than the Earth from the Sun), however, will limit planet formation to the hottest central regions.

“Over half of the binaries [in astronomical surveys] are wide enough to allow planet formation in the habitable zone of solar-type stars.” Quintana concludes. That fraction expands the catalogue of interesting stars significantly, but many possibilities remain unexplored.

For example, it is entirely possible for compact binary systems to share a protoplanetary disk the planetesimals would just orbit both stars at once. And there is no reason for just one of the stars to have planets!

Another open question in whether icy planetesimals, which normally form beyond 5 AU, can still reach the inner disk to deliver water to the rocky worlds. "It is more difficult," Quintana admits, "but there are many scenarios for having habitable planets in binary star systems." Most of the disk is not treated in these simulations, and there could be plenty of room around or between the two stars for comets and even gas giants to form. The water will probably still be available, but it is too soon to estimate how much of it might reach these worlds.

Physical simulations of planet formation have the potential to answer these questions and more. By the time Kepler and CoRoT start detecting Earth-like worlds, this line of research should have given us a good idea what to expect.

Earth’s carbon came from ancient collision with Mercury-like planet

The ratio of volatile elements in Earth’s mantle suggests that virtually all of the planet’s life-giving carbon came from a collision with an embryonic planet approximately 100 million years after Earth formed. Image credit: A. Passwaters/Rice University based on original courtesy of NASA/JPL-Caltech. Research by Rice University Earth scientists suggests that virtually all of Earth’s life-giving carbon could have come from a collision about 4.4 billion years ago between Earth and an embryonic planet similar to Mercury.

In a new study this week in Nature Geoscience, Rice petrologist Rajdeep Dasgupta and colleagues offer a new answer to a long-debated geological question: how did carbon-based life develop on Earth, given that most of the planet’s carbon should have either boiled away in the planet’s earliest days or become locked in Earth’s core?

Rajdeep Dasgupta. Image credit: Jeff Fitlow/Rice University. “The challenge is to explain the origin of the volatile elements like carbon that remain outside the core in the mantle portion of our planet,” said Dasgupta, who co-authored the study with lead author and Rice postdoctoral researcher Yuan Li, Rice research scientist Kyusei Tsuno and Woods Hole Oceanographic Institute colleagues Brian Monteleone and Nobumichi Shimizu.

Dasgupta’s lab specialises in recreating the high-pressure and high-temperature conditions that exist deep inside Earth and other rocky planets. His team squeezes rocks in hydraulic presses that can simulate conditions about 250 miles below Earth’s surface or at the core-mantle boundary of smaller planets like Mercury.

“Even before this paper, we had published several studies that showed that even if carbon did not vaporise into space when the planet was largely molten, it would end up in the metallic core of our planet, because the iron-rich alloys there have a strong affinity for carbon,” Dasgupta said.

Earth’s core, which is mostly iron, makes up about one-third of the planet’s mass. Earth’s silicate mantle accounts for the other two-thirds and extends more than 1,500 miles below Earth’s surface. Earth’s crust and atmosphere are so thin that they account for less than 1 percent of the planet’s mass. The mantle, atmosphere and crust constantly exchange elements, including the volatile elements needed for life.

If Earth’s initial allotment of carbon boiled away into space or got stuck in the core, where did the carbon in the mantle and biosphere come from?

Yuan Li. Image credit: Kyusei Tsuno. “One popular idea has been that volatile elements like carbon, sulfur, nitrogen and hydrogen were added after Earth’s core finished forming,” said Li, who is now a staff scientist at Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. “Any of those elements that fell to Earth in meteorites and comets more than about 100 million years after the solar system formed could have avoided the intense heat of the magma ocean that covered Earth up to that point.

“The problem with that idea is that while it can account for the abundance of many of these elements, there are no known meteorites that would produce the ratio of volatile elements in the silicate portion of our planet,” Li said.

In late 2013, Dasgupta’s team began thinking about unconventional ways to address the issue of volatiles and core composition, and they decided to conduct experiments to gauge how sulfur or silicon might alter the affinity of iron for carbon. The idea didn’t come from Earth studies, but from some of Earth’s planetary neighbours.

“We thought we definitely needed to break away from the conventional core composition of just iron and nickel and carbon,” Dasgupta recalled. “So we began exploring very sulfur-rich and silicon-rich alloys, in part because the core of Mars is thought to be sulfur-rich and the core of Mercury is thought to be relatively silicon-rich.

“It was a compositional spectrum that seemed relevant, if not for our own planet, then definitely in the scheme of all the terrestrial planetary bodies that we have in our solar system,” he said.

The experiments revealed that carbon could be excluded from the core &mdash and relegated to the silicate mantle &mdash if the iron alloys in the core were rich in either silicon or sulfur.

“The key data revealed how the partitioning of carbon between the metallic and silicate portions of terrestrial planets varies as a function of the variables like temperature, pressure and sulfur or silicon content,” Li said. A schematic depiction of proto Earth’s merger with a potentially Mercury-like planetary embryo, a scenario supported by new high pressure-temperature experiments at Rice University. Magma ocean processes could lead planetary embryos to develop silicon- or sulfur-rich metallic cores and carbon-rich outer layers. If Earth merged with such a planet early in its history, it could explain how Earth acquired its carbon and sulfur. Illustration credit: Rajdeep Dasgupta. The team mapped out the relative concentrations of carbon that would arise under various levels of sulfur and silicon enrichment, and the researchers compared those concentrations to the known volatiles in Earth’s silicate mantle.

“One scenario that explains the carbon-to-sulfur ratio and carbon abundance is that an embryonic planet like Mercury, which had already formed a silicon-rich core, collided with and was absorbed by Earth,” Dasgupta said. “Because it’s a massive body, the dynamics could work in a way that the core of that planet would go directly to the core of our planet, and the carbon-rich mantle would mix with Earth’s mantle.

“In this paper, we focused on carbon and sulfur,” he said. “Much more work will need to be done to reconcile all of the volatile elements, but at least in terms of the carbon-sulfur abundances and the carbon-sulfur ratio, we find this scenario could explain Earth’s present carbon and sulfur budgets.”

Every Place We Used to Think Was a Planet (Until We Knew Better)

We once considered the Sun a planet, and it took finding Uranus to decide that moons should really be their own category of thing. These are all the places in our solar system that were once planets—but now have far more suitable names.

The Sun and the Moon

When the Ptolemaic model of an Earth-centric universe held sway , planets were anything that wandered in the sky independently of orderly stars. That covered the five naked-eye visible planets, but also the most glaringly obvious candidates for, “Which of these are not like the others?” ever: the Moon and the Sun. Under this definition, Earth was clearly not a planet since all the planets orbited around it.

Ptolemaic model of the geocentric universe as illustrated in the 16th century.

The Sun kept its planetary status even after we figured out the other planets orbited it: the Tychonian model of the solar system kept the Earth in the center of the Solar System with the Sun in orbit around it and Mercury, Venus, Mars, Jupiter, and Saturn whirling around the star like demented moons. The Sun was finally demoted as the Copernicus model of the Solar System gained acceptance in the 17th century and we reluctantly conceded that we were the ones on a planet orbiting the Sun, not the other way around.

Likewise, the Moon was also eventually demoted—but, before that happened, it picked up a lot more company.

The Many Moons of Gas Giants

The main moons of both Jupiter and Saturn briefly joined the list of planets before helping reshape our views of solar system dynamics. The four Galilean moons of Jupiter — Callisto , Ganymede , Europa , and Io — joined the list of planets after their discovery in 1610. The five main moons of Saturn gradually joined the list with their discoveries — Titan in 1655, Iapetus and Rhea in 1671, and Tethys and Dione in 1684.

Observations of Jupiter’s four largest moons. Image credit: Galileo Galilei

This explosion of tiny planets orbiting bigger planets led to the creation of a whole new concept: moons. With a unique term all their own (and the final removal of our own moon from planet-status), scientists were able to start talking about these miniature worlds in a manner separate from their larger similar-yet-distinct companions. By the 18th century, the removal of moons and the discovery of Uranus brought the planet count to six.

Amusingly, keeping these worlds not planets has repeatedly reemerged in later redefinitions of the term. Ganymede is both the Solar System’s largest moon and the only one (so far!) with evidence of a magnetic field, while the massive Titan has an atmosphere and complex surface dynamics.

Ceres, the World that Still Confuses Us

In 1801, Giuseppe Piazzi accidentally discovered Ceres. Considering we’re still baffled on how to define it even with a spacecraft in orbit , it’s not surprising its discoverers added Ceres to the planet list. Today we alternate between calling it the largest asteroid, the only dwarf planet in the main asteroid belt, or that weird thing over there that’s similar yet different from everything else we’ve found in our solar system.

Pallas, Juno, Vesta, and an Explosion of Asteroids

Not long after finding Ceres, astronomers started finding a whole slew of similar objects in the same part of space while looking for a “missing planet” between Mars and Jupiter predicted by a now-discredited theory. Between 1845 and 1851, Pallas , Juno, Vesta , Astraea, Hebe, Iris, Flora, Metis, Hygiea, Parthenope, Victoria, Egeria, Irene, and Eunomia all joined the list of planets in our Solar System. They quickly picked up a unique name — asteroids, but were treated as yet more planets (or possibly the shattered aftermath of a planet’s destruction) in observation records.

The new asteroids even acquired those cool single-symbol alternate shorthand notation for ease of reference, although the growing list made the new symbols less elegant than their earlier predecessors. This crowded namespace for new symbols was indirectly what drove the decision to possibly reclassify these new worlds.

Annoyed by the complexity of the newer symbols, Johann Franz Encke published his 1854 guide to astronomical objects by streamlining the symbols to everything post-Vesta as simply a number in a circle. The alternate notation quickly gained popularity and sparked an unintended consequence in how the new discoveries were treated — some publications now listed them in numerical order-of-discovery instead of distance from the sun, while others put them in a special subsection isolated from other planetary news.

Astronomical symbols as of 1850. Image credit: Johann Franz Encke

The transition to separating asteroids from the planets was slow, painful, and inconsistent. The Nautical Almanac and Astronomical Ephemeris listed asteroid observations as “Minor Planets, Elements of” from 1841 until 1853, when it rearranged all the new discoveries with the more traditional list of planets. German publications started using Kleine Planeten (“tiny planets” following the notation switch in 854, with the Astronomische Nachrichten classifying them as a subcategory of planets from 1861 to 1932. In France, the Paris Observatory started pulling “petites planetes” from the main list in 1866, although Pallas, Juno, and Vesta did double-duty as both members of the list of main planets and as a preface to the asteroid index until 1868.

Binary Planets

In our solar system, there are no double planets where the two masses are virtually equal. Pluto / Charon, and Earth / Moon are the only candidates, but in both cases the primary is much large than the secondary.

In other star ststems, planets smaller than Neptune have not been detected at all. Double planets of any size have not been discovered either. That's not to say that they don't exist. Equipment needs to get a lot better to confidently conclude that.

Gravity probably would cancel out at that point, but it would still not be a stable point, similar to the L1, L2, & L3 points. The smallest of pertubations from a solar tide or other sources would be magnified over time, expelling an object from that point. Chaos would then take over.

The two objects could be as close together as the larger one's Roche limit. Tidal forces would probably seperate them even more over time.

By "abbitrairly close" do you mean like Earth / Moon? Naturally the objects would want to circularize their orbits,and external pertubations would prevent them from ever reaching perfect.

Random perturbations. There are no circular orbits, or if there are, they don't stay that way for long. It may be possible (although not probable) for two planets to form in the configuration being described, but I don't think they'd stay that way long enough for them to cool down when the star is forming.

I seem to recall that one of our members put several simulations of multi-body systems on their own website. Several were stable, although only for "perfect" universes. Once any sort of perturbations were introduced, the system decayed very rapidly (less than 10 orbits).

If you wait long enough, even in the absence of any external influences, the two 'planets' will collide. Why? Because the system loses energy through gravitational radiation, just like PSR1913+16, observations of which lead to Nobel prizes for Taylor and Hulse. Of course, if the planets have low masses, and their mutual orbit is very large, this time may be waayyy beyond a trillion years.

More likely, mutual tides (no 'planet' is perfectly rigid) will be the dominant factor, though all sorts of others may also be important (e.g. mass loss at the top of the atmospheres, encounters with other massive objects, passages through dense molecular clouds, differential radiation effects, collisions, mass accretion from interstellar grains, . ).

You'll need to keep the two planets further apart than the roche limit. This is only 2.5 planetary diameters when they have the same density, so they can get _very_ close before this happens, much closer than the earth & moon.

Here's a link to a worldbuilding website which discusses the Roche Limit

You might find the worldbuilding site interesting in and of itself, it offers technical information on the physics of "building" worlds to SF writers and would-be SF writers, so it talks a lot about the physics of "building" worlds.

Planets being very close together will undoubtedly tidal lock to each other.

The point at which the gravitatioanl attractions balance in a rotating coordiante system exits even when the planets have different masses. It's called the Lagrange point L1. It's a very interesting place which is very important to three body orbital dynamics. The dynamics allows for low energy orbital transfers via orbits that travel near these points - the math is a bit tricky, but it's gotten some publicity as the "Interplanetary Superhighway". The Genesis mission (which unortunately crashed when its chute failed to deploy), and a tour of Jupiters moons are two missions which have been planned using orbital dynamics based around the L1 points.

There's a SF book about a pair of orbiting worlds similar to what you describe called "Rocheworld" written by Robert Forward that you might be interested in. It's fiction, but it's "hard" fiction, written by a physicist. The writing from a literary point of view is not that great, alas.

I examined the problem of "twin Earths" once. I assumed a binary planet having each component habitable and of Earth's mass, with their mutual center of mass going around a star in a circular orbit with radius giving a subsolar temperature of 393.6K (same as Earth with respect to the sun).

For single habitable planets, not a moon of another planet, the star mass range is 0.8 to 1.5 solar masses. Twin Earths may occur only with stars in the very top end of this range: 1.3 to 1.5 solar masses. However, if a strong greenhouse effect can be presumed continuous, the allowable star mass can be lowered to about 1.1.

The upper bound on star mass is the result of an arbitrary decree that the star must remain on the main sequence a total of 3 billion years as a condition for any of its planets to become habitable. The luminosity is about proportionate to the mass raised to the fourth power. Big stars burn up faster than little stars do. So habitable planets in general occur only to main sequence stars of 1.5 solar masses or less.

The lower bound on the star's mass results from a condition that the twin Earths be neither rotationally bound to each other in mutual tidal lock nor tidally separated from each other by the star's gravity. Below a certain star mass, those two requirements are in conflict, meaning that the twin Earths, as defined, are not possible for stars whose masses are too low.

The planets' orbital distance from the star must remain at that having the required subsolar temperature, meaning that the distance between the twin-Earth barycenter and the star varies with the (about) square of the star's mass. Lessen the star's mass, and you even more greatly lessen the radius at which the twin-Earth orbits.

The tidal influence of the star increases inversely in proportion to the cube of the distance and directly in proportion to the star's mass. Using again the mass-luminosity relationship, the tidal force is proportional to the star's mass raised to the power of -5 (minus five, or thereabout).

In other words, as stars of progressively lower mass are considered, the components of the twin-Earth are limited to smaller and smaller separations. This is a greatest permitted separation.

Assuming that tidal friction spindown for an Earthlike planet occurs over three billion years when the components' are near enough that their tidal drag, one upon the other, is equal to that of the sun on Venus, there's a smallest permitted separation that will keep the pair freely rotating.

The greatest permitted separation becomes less than the least permitted separation if the star's mass is less than (about) 1.3 solar masses. So freely rotating twin Earths are possible only to stars of 1.3-1.5 solar masses.

Of course, if you don't mind month-or-so long nights, then you can dispense with the smallest permitted separation, and in that case you can put the planets as closely together as you wish, until tidal heating or the Roche limit puts an end to the habitability requirement. I assumed that free rotation was necessary to habitability.

Ken Ham Really Doesn’t Understand Science

In 2014, popular science communicator Bill Nye “debated” creationist Ken Ham in a live webcast on YouTube. The event went pretty much as expected Nye presented levelheaded evidence that science works, that evolution is real, and the Universe is very old, while Ham used bad logic, cherry-picking, and blatant twisting of scientific claims.

At the time (and still today) I think Nye made the right decision to participate in the event. Ham runs the Answers in Genesis ministry, and also the Creation Museum in Kentucky, and is well-known for his outrageous statements. It might seem silly to elevate the debate by paying any attention at all to Ham, but that ignores the fact that polls consistently show that half of the American population believes in some form of creationism.

We ignore this at our own peril.

Debating creationists is slippery. When your opponent doesn’t have to adhere to facts or logic, it’s tricky to find traction. My friend Zach Weinersmith once wrote that it’s not that most creationists are anti-evolution, it’s that they’re anti-some distorted version of it told to them by their pastors.

He’s completely correct. That became even clearer to me when, shortly after the debate, BuzzFeed posted an article called “22 Messages From Creationists to People Who Believe in Evolution”. It was clear from the questions asked that the creationists involved had no idea about how evolution—even science itself—worked. The questions were universally based on false premises, a distortion of the science that made it actually pretty easy to answer those supposedly “gotcha” queries.

So I did answer them, in a post titled “Answers for Creationists.” I politely, but firmly, answered the questions posed, with links to expert sources if anyone wanted to dig a little deeper. It became one of my most popular articles of all time.

But as Zach pointed out, while these questions have been answered countless times, they still get asked. Why? The answer is obvious: Because the people asking those questions are still getting their information from people like Ken Ham who refuse to listen to anything science has to say and who still propagate falsehoods.

And I know this for a fact. That’s because Ham took to Twitter recently, posting a series of tweets that are not just wrong, but completely wrong, again demonstrating not just a misunderstanding of the topic, but a deep—I daresay fundamental—lack of understanding of even the most basic facts about the science he’s trying to deny.

It’s enlightening to look over what he said, because, again, a lot of people listen to him. And, like my previous post about answering creationists’ questions, I address this not to Ham, but to those who might listen to him: Perhaps you’ve heard these claims, and wondered about them. Here’s what science has to say about them.

First up: a bad Moon rising.

The recession of the moon is evidence confirming the moon cannot be 4+ billion years old--it would have touched the earth way before then

&mdash Ken Ham (@aigkenham) May 3, 2016

Like most such claims, it’s based on a kernel of truth: The Moon is in fact receding from the Earth, by a rate of about 4 centimeters per year. That’s roughly at the same rate your fingernails grow. The motion is due to the way Earth’s gravity affects the Moon, through the tidal force.

This means that, in the past, the Moon was closer to the Earth. And this is where—if you believe Ham—you run into a problem. The rate at which the Moon recedes depends very strongly on its distance from the Earth. In the past, when it was closer, it would have receded even more quickly.

According to Ham’s thinking, that means the Moon must be younger than science would say, only a billion or so years old at the most. A relatively simple calculation shows that, given the faster recession in the past, the Moon would have been touching the Earth about a billion years ago.

But this is incorrect. The real problem here is a common one with claims like this: taking a trend and simply running it backward or forward as if nothing ever changes.

In this case, there are other factors that affect the Moon’s recession rate, and Ham ignores them. For example, the shape of the continents and shorelines on Earth has a large effect as well (because the tidal interaction depends strongly on the way the water and seabed on Earth interact). It turns out that we have an anomalously high rate of recession today many studies show that in the past the rate was actually slower.

Yes, initially, right after the Moon formed, it receded very rapidly indeed. But as it receded, other factors came into play. The numbers as we see them now easily allow a 4.5 billion year old Moon, just as scientific theory predicts.

Moving on, a little closer to home:

Earth's magnetic field is decaying--the earth couldn't be millions of years old-life couldn't have existed with a stronger field in the past

&mdash Ken Ham (@aigkenham) May 3, 2016

Again, a nugget of truth: The Earth’s magnetic field is changing. It does this all the time it’s generated deep inside the Earth by our very hot iron core. The inner core is solid, but the outer core is liquid. The heat from the inner core causes the molten iron to rise, cool, and sink again. The iron is so hot it’s ionized (electrons are stripped from their atoms), and when an ionized fluid moves, it can generate a magnetic field. Changes in the liquid outer core change the Earth’s magnetic field, which we can see. For example, the magnetic poles of the Earth wander and the field strength changes.

New Horizons’ next target might be a binary pair

One artist’s concept of Kuiper Belt object 2014 MU69, the next flyby target for NASA’s New Horizons mission. This binary concept is based on telescope observations made at Patagonia, Argentina, on July 17, 2017, when MU69 passed in front of a star. New Horizons theorize that it could be a single body with a large chunk taken out of it, or two bodies that are close together or even touching.
Credit: NASA/JHUAPL/SwRI/Alex Parker

Ground observations of the New Horizons spacecraft’s next target last month revealed the distant object, lurking in the outer Solar System more than four billion miles from Earth, might have an unconventional elongated shape, or even consist of two icy bodies orbiting one another in an age-old cosmic dance.

The New Horizons team deployed 24 mobile telescopes to Chubut and Santa Cruz provinces in Argentina to catch the tiny world, officially named 2014 MU69, briefly blotting out light from a star. Called an occultation, the event helped scientists learn more about the robotic mission’s next target, including its size, shape, orbit and the environment around it.

Two years after making the first close-up encounter with Pluto, NASA’s plutonium-powered New Horizons probe is speeding toward a flyby of 2014 MU69 on Jan. 1, 2019.

A handful of detections from last month’s field campaign in Argentina improved scientists’ understanding of 2014 MU69’s shape. Researchers said the object could be a “extreme prolate spheroid” — akin to a skinny football — or a binary pair in which two bodies might be gravitationally locked close together, or even touching, according to NASA.

“This new finding is simply spectacular,” said Alan Stern, principal investigator on the New Horizons mission from the Southwest Research Institute in Boulder, Colorado. “The shape of MU69 is truly provocative, and could mean another first for New Horizons going to a binary object in the Kuiper Belt. I could not be happier with the occultation results, which promise a scientific bonanza for the flyby.”

Scientists have set an upper limit on the likely size of MU69 at 20 miles (30 kilometres) long. If there are two objects, each one is likely 9-12 miles (15-20 kilometres) in diameter, NASA said in a statement.

Now you see it, now you don’t: NASA’s New Horizons team trained mobile telescopes on an unnamed star (center) from rural Argentina on July 17, 2017. A Kuiper Belt object 4.1 billion miles from Earth — known as 2014 MU69 — briefly blocked the light from the background star, in what’s called an occultation. The time difference between frames is 200 milliseconds, or 0.2 seconds. This data helps scientists to better measure the shape, size and environment around the object the New Horizons spacecraft will fly by this ancient relic of solar system formation on Jan. 1, 2019. Credit: NASA/JHUAPL/SwRI

Orbiting in the faraway Kuiper Belt, MU69 will become the most distant object ever visited by a spacecraft when New Horizons zips by on New Year’s Day 2019. NASA officials expect to give the target a new name before New Horizons makes its flyby at a relative velocity of more than 9 miles per second (14 kilometres per second).

Miniature worlds like 2014 MU69 are likely the leftover ice and rock fragments that formed larger objects like Pluto, the moons of some Uranus and Neptune, and other dwarf planets in the outer solar system.

The Kuiper Belt is a ring of ancient icy remnants from the earliest part of the solar system’s 4.6 billion-year history circling the sun beyond the orbit of Neptune. Its population includes continent-sized words like Pluto and the even-farther dwarf planet Eris, and perhaps hundreds of thousands of objects the size of 2014 MU69 or larger.

A search by the Hubble Space Telescope discovered MU69 in 2014 after other surveys turned up no suitable targets for New Horizons following its encounter with Pluto on July 14, 2015. A series of thruster firings steered New Horizons on a new course for MU69 soon after the Pluto flyby.

Observations by Hubble and the European Space Agency’s Gaia mission pinpointed MU69’s orbit, telling scientists when the object would pass in front of stars, casting shadows on Earth’s surface. Watching MU69’s passage between Earth and a distant star was a chance to learn more about the object than astronomers could ascertain from conventional observations. The tiny world appears as a fuzzy dot of light even through Hubble.

An occultation visible June 3 from Argentina and South Africa was the first chance to study MU69’s shape and size. Scientists boarded NASA’s flying infrared astronomy observatory, called SOFIA, for a similar July 10 opportunity to search for debris around MU69 that could pose a hazard to New Horizons.

MU69 blocked a brighter star July 17, giving scientists their best view of the object’s shape.

While data are still being analysed, scientists probably will not know MU69’s true shape until New Horizons is on final approach in December 2018, Stern wrote in an email to Spaceflight Now.

“These exciting and puzzling results have already been key for our mission planning, but also add to the mysteries surrounding this target leading into the New Horizons encounter with MU69, now less than 17 months away,” said Marc Buie, the New Horizons co-investigator who led the observation campaign.

Follow Stephen Clark on Twitter: @StephenClark1.

Astronomy Calendar of Celestial Events for Calendar Year 2025

This astronomy calendar of celestial events contains dates for notable celestial events including moon phases, meteor showers, eclipses, oppositions, conjunctions, and other interesting events. Most of the astronomical events on this calendar can be seen with unaided eye, although some may require a good pair of binoculars for best viewing. Many of the events and dates that appear here were obtained from the U.S. Naval Observatory, The Old Farmer's Almanac., and the American Meteor Society. Events on the calendar are organized by date and each is identified with an astronomy icon as outlined below. Please note that all dates and times are given in Coordinated Universal Time (UTC) must be converted to your local date and time. You can use the UTC clock widget below to figure out how many hours to add or subtract for your local time.

January 3, 4 - Quadrantids Meteor Shower. The Quadrantids is an above average shower, with up to 40 meteors per hour at its peak. It is thought to be produced by dust grains left behind by an extinct comet known as 2003 EH1, which was discovered in 2003. The shower runs annually from January 1-5. It peaks this year on the night of the 3rd and morning of the 4th. The crescent moon will set early in the evening, leaving dark skies for what should be an excellent show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Bootes, but can appear anywhere in the sky.

January 10 - Venus at Greatest Eastern Elongation. The planet Venus reaches greatest eastern elongation of 47.2 degrees from the Sun. This is the best time to view Venus since it will be at its highest point above the horizon in the evening sky. Look for the bright planet in the western sky after sunset.

January 13 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 22:28 UTC. This full moon was known by early Native American tribes as the Wolf Moon because this was the time of year when hungry wolf packs howled outside their camps. This moon has also been know as the Old Moon and the Moon After Yule.

January 16 - Mars at Opposition. The red planet will be at its closest approach to Earth and its face will be fully illuminated by the Sun. It will be brighter than any other time of the year and will be visible all night long. This is the best time to view and photograph Mars. A medium-sized telescope will allow you to see some of the dark details on the planet's orange surface.

January 29 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 12:37 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

February 12 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 13:55 UTC. This full moon was known by early Native American tribes as the Snow Moon because the heaviest snows usually fell during this time of the year. Since hunting is difficult, this moon has also been known by some tribes as the Hunger Moon, since the harsh weather made hunting difficult.

February 28 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 00:46 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

March 8 - Mercury at Greatest Eastern Elongation. The planet Mercury reaches greatest eastern elongation of 18.2 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the evening sky. Look for the planet low in the western sky just after sunset.

March 14 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 06:56 UTC. This full moon was known by early Native American tribes as the Worm Moon because this was the time of year when the ground would begin to soften and the earthworms would reappear. This moon has also been known as the Crow Moon, the Crust Moon, the Sap Moon, and the Lenten Moon.

March 14 - Total Lunar Eclipse. A total lunar eclipse occurs when the Moon passes completely through the Earth's dark shadow, or umbra. During this type of eclipse, the Moon will gradually get darker and then take on a rusty or blood red color. The eclipse will be visible throughout all of North America, Mexico, Central America, and South America. (NASA Map and Eclipse Information)

March 20 - March Equinox. The March equinox occurs at 08:58 UTC. The Sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world. This is also the first day of spring (vernal equinox) in the Northern Hemisphere and the first day of fall (autumnal equinox) in the Southern Hemisphere.

March 29 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 11:00 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

March 29 - Partial Solar Eclipse. A partial solar eclipse occurs when the Moon covers only a part of the Sun, sometimes resembling a bite taken out of a cookie. A partial solar eclipse can only be safely observed with a special solar filter or by looking at the Sun's reflection. This partial eclipse will be visible throughout Greenland and most of northern Europe and northern Russia. It will be best seen from Canada with 93% coverage.
(NASA Map and Eclipse Information)

April 13 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 00:24 UTC. This full moon was known by early Native American tribes as the Pink Moon because it marked the appearance of the moss pink, or wild ground phlox, which is one of the first spring flowers. This moon has also been known as the Sprouting Grass Moon, the Growing Moon, and the Egg Moon. Many coastal tribes called it the Fish Moon because this was the time that the shad swam upstream to spawn.

April 21 - Mercury at Greatest Western Elongation. The planet Mercury reaches greatest western elongation of 27.4 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the morning sky. Look for the planet low in the eastern sky just before sunrise.

April 22, 23 - Lyrids Meteor Shower. The Lyrids is an average shower, usually producing about 20 meteors per hour at its peak. It is produced by dust particles left behind by comet C/1861 G1 Thatcher, which was discovered in 1861. The shower runs annually from April 16-25. It peaks this year on the night of the night of the 22nd and morning of the 23rd. These meteors can sometimes produce bright dust trails that last for several seconds. The thin crescent moon will not pose much of a problem so this should be a good show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Lyra, but can appear anywhere in the sky.

April 27 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 19:32 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

May 6, 7 - Eta Aquarids Meteor Shower. The Eta Aquarids is an above average shower, capable of producing up to 60 meteors per hour at its peak. Most of the activity is seen in the Southern Hemisphere. In the Northern Hemisphere, the rate can reach about 30 meteors per hour. It is produced by dust particles left behind by comet Halley, which has been observed since ancient times. The shower runs annually from April 19 to May 28. It peaks this year on the night of May 6 and the morning of the May 7. The waxing gibbous moon will block out some of the fainter meteors this year. But if you are patient, you should still should be able to catch a some of the brighter ones. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Aquarius, but can appear anywhere in the sky.

May 12 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 16:57 UTC. This full moon was known by early Native American tribes as the Flower Moon because this was the time of year when spring flowers appeared in abundance. This moon has also been known as the Corn Planting Moon and the Milk Moon.

May 27 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 03:04 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

May 31 - Venus at Greatest Western Elongation. The planet Venus reaches greatest eastern elongation of 45.9 degrees from the Sun. This is the best time to view Venus since it will be at its highest point above the horizon in the morning sky. Look for the bright planet in the eastern sky before sunrise.

June 11 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 07:45 UTC. This full moon was known by early Native American tribes as the Strawberry Moon because it signaled the time of year to gather ripening fruit. It also coincides with the peak of the strawberry harvesting season. This moon has also been known as the Rose Moon and the Honey Moon.

June 21 - June Solstice. The June solstice occurs at 02:40 UTC. The North Pole of the earth will be tilted toward the Sun, which will have reached its northernmost position in the sky and will be directly over the Tropic of Cancer at 23.44 degrees north latitude. This is the first day of summer (summer solstice) in the Northern Hemisphere and the first day of winter (winter solstice) in the Southern Hemisphere.

June 25 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 10:33 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

July 4 - Mercury at Greatest Eastern Elongation. The planet Mercury reaches greatest eastern elongation of 25.9 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the evening sky. Look for the planet low in the western sky just after sunset.

July 10 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 20:38 UTC. This full moon was known by early Native American tribes as the Buck Moon because the male buck deer would begin to grow their new antlers at this time of year. This moon has also been known as the Thunder Moon and the Hay Moon.

July 24 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 19:13 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

July 28, 29 - Delta Aquarids Meteor Shower. The Delta Aquarids is an average shower that can produce up to 20 meteors per hour at its peak. It is produced by debris left behind by comets Marsden and Kracht. The shower runs annually from July 12 to August 23. It peaks this year on the night of July 28 and morning of July 29. The crescent moon will set early in the evening, leaving dark skies for what should be an excellent show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Aquarius, but can appear anywhere in the sky.

August 9 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 07:56 UTC. This full moon was known by early Native American tribes as the Sturgeon Moon because the large sturgeon fish of the Great Lakes and other major lakes were more easily caught at this time of year. This moon has also been known as the Green Corn Moon and the Grain Moon.

August 12, 13 - Perseids Meteor Shower. The Perseids is one of the best meteor showers to observe, producing up to 60 meteors per hour at its peak. It is produced by comet Swift-Tuttle, which was discovered in 1862. The Perseids are famous for producing a large number of bright meteors. The shower runs annually from July 17 to August 24. It peaks this year on the night of August 12 and the morning of August 13. The waning gibbous moon will block out all but the brightest meteors this year. But if you are patient, you may still be able to catch quite a few good ones. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Perseus, but can appear anywhere in the sky.

August 19 - Mercury at Greatest Western Elongation. The planet Mercury reaches greatest western elongation of 18.6 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the morning sky. Look for the planet low in the eastern sky just before sunrise.

August 23 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 06:08 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

September 7 - Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 18:10 UTC. This full moon was known by early Native American tribes as the Corn Moon because the corn is harvested around this time of year. This moon is also known as the Harvest Moon. The Harvest Moon is the full moon that occurs closest to the September equinox each year.

September 7 - Total Lunar Eclipse. A total lunar eclipse occurs when the Moon passes completely through the Earth's dark shadow, or umbra. During this type of eclipse, the Moon will gradually get darker and then take on a rusty or blood red color. The eclipse will be visible throughout all of Asia and Australia and the central and eastern parts of Europe and Africa. (NASA Map and Eclipse Information)

September 21 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 19:55 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

September 21 - Partial Solar Eclipse. A partial solar eclipse occurs when the Moon covers only a part of the Sun, sometimes resembling a bite taken out of a cookie. A partial solar eclipse can only be safely observed with a special solar filter or by looking at the Sun's reflection. This partial eclipse will only be visible in New Zealand, Antarctica, and the southern Pacific Ocean. It will be best seen from New Zealand with 76% coverage.
(NASA Map and Eclipse Information)

September 21 - Saturn at Opposition. The ringed planet will be at its closest approach to Earth and its face will be fully illuminated by the Sun. It will be brighter than any other time of the year and will be visible all night long. This is the best time to view and photograph Saturn and its moons. A medium-sized or larger telescope will allow you to see Saturn's rings and a few of its brightest moons.

September 22 - September Equinox. The September equinox occurs at 18:17 UTC. The Sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world. This is also the first day of fall (autumnal equinox) in the Northern Hemisphere and the first day of spring (vernal equinox) in the Southern Hemisphere.

September 23 - Neptune at Opposition. The blue giant planet will be at its closest approach to Earth and its face will be fully illuminated by the Sun. It will be brighter than any other time of the year and will be visible all night long. This is the best time to view and photograph Neptune. Due to its extreme distance from Earth, it will only appear as a tiny blue dot in all but the most powerful telescopes.

October 7 - Full Moon, Supermoon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 03:49 UTC. This full moon was known by early Native American tribes as the Hunters Moon because at this time of year the leaves are falling and the game is fat and ready to hunt. This moon has also been known as the Travel Moon and the Blood Moon. This is also the first of three supermoons for 2025. The Moon will be near its closest approach to the Earth and may look slightly larger and brighter than usual.

October 7 - Draconids Meteor Shower. The Draconids is a minor meteor shower producing only about 10 meteors per hour. It is produced by dust grains left behind by comet 21P Giacobini-Zinner, which was first discovered in 1900. The Draconids is an unusual shower in that the best viewing is in the early evening instead of early morning like most other showers. The shower runs annually from October 6-10 and peaks this year on the the night of the 7th. Unfortunately the glare from the nearly full moon will block most of the meteors this year. Combined with the low hourly rate it would probably be best to skip this one unless you are really patient. Best viewing will be in the early evening from a dark location far away from city lights. Meteors will radiate from the constellation Draco, but can appear anywhere in the sky.

October 21 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 12:26 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

October 21, 22 - Orionids Meteor Shower. The Orionids is an average shower producing up to 20 meteors per hour at its peak. It is produced by dust grains left behind by comet Halley, which has been known and observed since ancient times. The shower runs annually from October 2 to November 7. It peaks this year on the night of October 21 and the morning of October 22. This is an excellent year for the Orionids. The moon will be absent all night long, leaving dark skies for what should be an excellent show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Orion, but can appear anywhere in the sky.

October 29 - Mercury at Greatest Eastern Elongation. The planet Mercury reaches greatest eastern elongation of 23.9 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the evening sky. Look for the planet low in the western sky just after sunset.

November 4, 5 - Taurids Meteor Shower. The Taurids is a long-running minor meteor shower producing only about 5-10 meteors per hour. It is unusual in that it consists of two separate streams. The first is produced by dust grains left behind by Asteroid 2004 TG10. The second stream is produced by debris left behind by Comet 2P Encke. The shower runs annually from September 7 to December 10. It peaks this year on the the night of November 4. Unfortunately the glare form the full moon will hide most of the meteors this year. If you are really patient, you may still be able to catch a few bright ones. Best viewing will be just after midnight from a dark location far away from city lights. Meteors will radiate from the constellation Taurus, but can appear anywhere in the sky.

November 5 - Full Moon, Supermoon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 13:21 UTC. This full moon was known by early Native American tribes as the Beaver Moon because this was the time of year to set the beaver traps before the swamps and rivers froze. It has also been known as the Frosty Moon and the Dark Moon. This is also the second of three supermoons for 2025. The Moon will be near its closest approach to the Earth and may look slightly larger and brighter than usual.

November 17, 18 - Leonids Meteor Shower. The Leonids is an average shower, producing up to 15 meteors per hour at its peak. This shower is unique in that it has a cyclonic peak about every 33 years where hundreds of meteors per hour can be seen. That last of these occurred in 2001. The Leonids is produced by dust grains left behind by comet Tempel-Tuttle, which was discovered in 1865. The shower runs annually from November 6-30. It peaks this year on the night of the 17th and morning of the 18th. This should be an excellent year for the Leonids. The thin, crescent moon won't be much of a problem and skies will be dark enough for what should be an great show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Leo, but can appear anywhere in the sky.

November 20 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 06:49 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

November 21 - Uranus at Opposition. The blue-green planet will be at its closest approach to Earth and its face will be fully illuminated by the Sun. It will be brighter than any other time of the year and will be visible all night long. This is the best time to view Uranus. Due to its distance, it will only appear as a tiny blue-green dot in all but the most powerful telescopes.

December 4 - Full Moon, Supermoon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 23:15 UTC. This full moon was known by early Native American tribes as the Cold Moon because this is the time of year when the cold winter air settles in and the nights become long and dark. This moon has also been known as the Long Nights Moon and the Moon Before Yule. This is also the last of three supermoons for 2025. The Moon will be near its closest approach to the Earth and may look slightly larger and brighter than usual.

December 7 - Mercury at Greatest Western Elongation. The planet Mercury reaches greatest western elongation of 20.7 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the morning sky. Look for the planet low in the eastern sky just before sunrise.

December 13, 14 - Geminids Meteor Shower. The Geminids is the king of the meteor showers. It is considered by many to be the best shower in the heavens, producing up to 120 multicolored meteors per hour at its peak. It is produced by debris left behind by an asteroid known as 3200 Phaethon, which was discovered in 1982. The shower runs annually from December 7-17. It peaks this year on the night of the 13th and morning of the 14th. The second quarter moon will block some of the fainter meteors this year, but the Geminids are so numerous that it should still be a good show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Gemini, but can appear anywhere in the sky.

December 20 - New Moon. The Moon will located on the same side of the Earth as the Sun and will not be visible in the night sky. This phase occurs at 01:45 UTC. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

December 21 - December Solstice. The December solstice occurs at 15:02 UTC. The South Pole of the earth will be tilted toward the Sun, which will have reached its southernmost position in the sky and will be directly over the Tropic of Capricorn at 23.44 degrees south latitude. This is the first day of winter (winter solstice) in the Northern Hemisphere and the first day of summer (summer solstice) in the Southern Hemisphere.

December 21, 22 - Ursids Meteor Shower. The Ursids is a minor meteor shower producing about 5-10 meteors per hour. It is produced by dust grains left behind by comet Tuttle, which was first discovered in 1790. The shower runs annually from December 17-25. It peaks this year on the the night of the 21st and morning of the 22nd. The thin, crescent moon will set early in the evening, leaving dark skies for what should be a good show. Best viewing will be just after midnight from a dark location far away from city lights. Meteors will radiate from the constellation Ursa Minor, but can appear anywhere in the sky.