Astronomy

Can you see city lights on the Moon from Earth?

Can you see city lights on the Moon from Earth?


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This is the opposite of another question. That question is about whether you could see cities on Earth if you were standing on the Moon.

Let's there are cities on the Moon and you're standing on the Earth on a clear night. Could you see the city lights?

If you're looking at Earth cities from the Moon, your line of sight is not affected by atmospheric turbulence because the Moon is airless. But if you are on Earth, then you have to look through the turbulent atmosphere to see faint lights. So you won't have to put up with the turbulence that makes stars look blurry or twinkley from the Earth.

But if you're on the Earth, any city lights on the Moon might look blurry or twinkley from our atmospheric turbulence. If it helps, imagine yourself at the top of a mountain so there is less atmosphere to look through and hence less turbulence.

In this picture of the Moon (and Venus in the background), imagine cities on dark part of the Moon's surface facing Earth. Those city lights should be easier to see than cities within the lit crescent.


It is possible but unlikely. Here is a really good 'Science 2.0' article about the possibility (http://www.science20.com/robert_inventor/could_you_see_moon_city_lights_or_a_greenhouse_from_earth_just_for_fun-157480). Essentially, you likely wouldn't see the light on Moon settlements because there would need to have many thousands of bright lights and windows- both of these would be impractical on a moon base (windows let in radiation and are expensive, and bright lights waste valuable power). Furthermore, in order to reach a magnitude of brightness to constitute as visible, there would have to be a very large amount settlements concentrated together.


Can you see city lights on the Moon from Earth? - Astronomy

If there were humans on the Moon - would we see the settlement lights from the Earth? For instance during a thin crescent Moon - could we see the lights of civilization in the parts of the Moon in darkness?

It's a fun question to answer I think, so let's give it a go.

We can work it out backwards from the brightness of the full Moon.

Looking out on the lunar surface from inside a Moon city, frame from the 1965 Russian film Luna


Explained: What Astronauts On The Moon Would See And Feel During This Week’s Total Lunar Eclipse

With the lunar horizon in the foreground, the Earth will pass in front of the Sun on Wednesday, May . [+] 26, 2021, revealing the red ring of sunrises and sunsets along the limb of the Earth.

NASA's Scientific Visualization Studio

Wednesday’s total lunar eclipse—the so-called “Blood Moon”—will see the lunar surface turn a reddish-copper color for 14 minutes and 30 seconds.

Since Earth will be aligned with the Sun and the Moon, our atmosphere will filter the Sun’s light onto the Moon as it enters the Earth’s shadow, essentially projecting thousands of sunrises and sunsets onto the lunar surface.

That’s the glowing red full Moon those west of the Mississippi will see in the early hours of Wednesday, May 26, 2021, but what would the event look like from the Moon’s surface itself?

It would be nothing less than a total eclipse of the Sun by the Earth!

With Earth hiding the Sun, astronauts on the surface would see a red ring—the sum of all Earth’s sunrises and sunsets—around the limb of the Earth.

“You would look up and see the Earth, potentially also the city lights on Earth, and you would notice the ground around you turn red,” said Dr. Noah Petro, Project Scientist for NASA’s Lunar Reconnaissance Orbiter mission that’s currently orbiting the Moon.

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It would also get really cold.

“The lunar surface then cools down substantially during an eclipse as the Moon goes from intense midday Sun to being in darkness,” said Petro. “Hopefully you wouldn’t feel the cooling through your spacesuit.” However, the ground around would cool substantially.

“It would be a pretty immersive affect the same way as on on Earth during a total solar eclipse when shadows look different and the atmosphere around you cools,” said Petro.

A lunar eclipse can be a risky time to have a space mission on the Moon.

“It depends on what that mission and its experiments are designed to survive, but it puts your equipment into a totally different thermal regime,” said Petro. “During the Apollo missions the astronauts were not going to be on the Moon during an eclipse, but the experiments they left behind were.”

Day-night cycles are, of course, normal on the Moon. “The one big difference of course, is that it's gets really hot and then it gets cold really quickly, so that thermal change is pretty dramatic—and dramatic temperature shifts can do strange things,” said Petro, mentioning windshields that crack in temperature extremes.

Plenty of science can be done during a total lunar eclipse and NASA’s Lunar Reconnaissance Orbiter (LRO) will, on Wednesday, measure the temperature change on the lunar surface.

Will it survive the sudden onset of cold?

With no sunlight to shine on the solar panels that power its heaters, a spacecraft in orbit can freeze during a total lunar eclipse unless it’s been specifically designed to cope with that challenge.

The LRO is designed to withstand an eclipse.“We've been at the Moon now for 12 years so we’ve gone through a number of eclipses and we know how the spacecraft will respond,” said Petro. “But early on in the mission, we didn’t, so we were very cautious.”

NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE)—a robotic probe that orbited the Moon in 2013/2014—was purposefully designed not to withstand a total lunar eclipse, but it just managed to survive, regardless.

“Because it’s a very short eclipse we know that the battery will not completely deplete during the eclipse and so we can leave the one experiment on to measure the temperature change,” said Petro about LRO this week. “If it were a longer eclipse we might not do it,”

So for missions to the Moon lunar eclipses have become engineering mileposts that have to be planned for in advance.

A total lunar eclipse occurs when a full Moon passes through Earth’s 870,000 miles/1.4 million km long shadow in space. That happens just occasionally, and it can take anywhere from 105 minutes (like in 2018) to just five minutes (like in 2015).

On May 26, 2021 it will last for such a short time because instead of traveling through the center of Earth’s shadow it will pass through its northern part, just 21 miles (34 km) from its outer edge. So the Moon’s northern limb is predicted to be rather bright during totality.

Either way, it’s an event not to be missed if you happen to be on the night-side of Earth at the right time.


What to observe on the Earth from the Moon

I wonder if we could see the flag they left behind when they did the earth landings.

Nah, it rotted quickly and what bits and pieces were left were packed into various bird nests as insulation.

#27 Saint Aardvark

Neat thread! Some thoughts:

  • Aurora! I'd love to see how much of the Northern/Southern Lights you could see dancing around the poles.
  • Iridium flares -- different angles, of course, but would some be visible from the moon?
  • Ditto the ISS.
  • I wonder if you'd be able to spot the occasional fireball entering Earth's atmosphere. The night side would be an obvious target, of course, but what about something like the Chelyabinsk meteor with its daytime flash?
  • Would rocket launches be visible?
  • Algae blooms

And of course, it would be a really interesting (read: hard) engineering problem to get a scope working on the moon. I think the suggestion for a glass dome might be the best idea the only alternative I could think of would be a custom helmet that accommodated eyepieces. And let's not even think about moon dust in a drive motor, or on an objective lens or mirror.

#28 Edd Weninger

No eyepieces needed. As we do from Earth, sensors of various types to view in real time or record data.

I'm a weather buff, I'd probably watch that during the full Earth time, and other things during dark Earth time.

#29 Dick Jacobson

A lunar eclipse would be gorgeous. Imagine a copper-colored ring around the Earth, with lighter and darker areas depending on clouds. Part of the Sun's corona might be visible, though not as much as in a total solar eclipse from Earth. A solar eclipse (on Earth) would be interesting too, watching the Moon's shadow move across the Earth.

#30 thomasr

A lunar eclipse would be gorgeous. Imagine a copper-colored ring around the Earth, with lighter and darker areas depending on clouds. Part of the Sun's corona might be visible, though not as much as in a total solar eclipse from Earth. A solar eclipse (on Earth) would be interesting too, watching the Moon's shadow move across the Earth.

Somehow, I find photos of the Earth during a solar eclipse - with than ominous round shadow - to be unsettling to look at. Anyone else feel the same way?

#31 csrlice12

I could be a volcano monitor. letting people know the volcano erupted

. oh, Iceland, the volcano erupted.

#32 Wade J

The Earth is so bright that a lot of Astronomers use a earth filter to dim the image. Not me. With no atmosphere you can crank up the power. I use my Nagler 3-6 Zoom with my 12.5 inch dob. 300 to 600 power with no atmosphere distortion.

#33 Cotts

On the moon with no atmosphere to mess with the viewing experience, I would hope to be on the 'other side' of the moon, facing away from earth. Don't need no stinkin' earth messin' up my views!

Yes, you would go from day to full earth and back. Never a dark sky.

Not exactly. Someone on the 'far' side of the moon will never see Earth in the sky. They would have about 14 continuous 24-hour periods of 100% complete darkness. Then 14 days of the sun being above the horizon. But the sky away from the sun would be just as black as night - no atmosphere to scatter the sun's light.

As for resolving detail. it is not unreasonable to be able to distinguish a contrast feature around 1" across with a great variety of good telescopes. Some will go a bit under 1" but let's use 1" as a guide.

1degree at the Earth-Moon mean distance of 240 000 miles amounts to about 4200 miles so 1/3600 of a degree (1") will subtend about 1.2 miles.

So the Suez canal? Nope. Great Wall of China? Heck Nope! Small Islands like Pitcairn, Montserrat, Galapagos would be easy in any telescope assuming sufficient contrast. Would the green/brown of an island be easy to see against the blue/gray of the sea? Contrast might be the more limiting factor.

Concerning an Iridium Flare. A typical flare is -5 magnitude and is approx 400 miles away from us. The moon is 600 times further away so, with the inverse square law, the flare would be 360 000 times fainter which would be at least 10 magnitudes fainter. Probably not visible from the moon naked eye.

The inverse square law would probably reduce big city lights by a large factor as well. Maybe visible in a telescope along with lightning. Aurora?? No idea - probably could be imaged with a longish exposure.


Illustration of the city lights on a dark Earth during a solar eclipse. - stock illustration

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City lights could reveal E.T. civilization

Researchers suggest the bright lights of cities, which are clearly visible on a planet even from space, have the potential to reveal the existence of alien life on other planets.

In the search for extraterrestrial intelligence, astronomers have hunted for radio signals and ultra-short laser pulses. But someday – according to Avi Loeb of Harvard-Smithsonian Center for Astrophysics and Edwin Turner of Princeton University – we might want to look for city lights.

They point out that, as our technology has moved from radio and TV broadcasts to cable and fiber optics, we have become less detectable to aliens. If the same is true of extraterrestrial civilizations, then artificial lights might be the best way to spot them from afar.

Loeb and Turner calculate that today’s best telescopes ought to be able to see lights like those of Earth’s biggest city – Tokyo – at the distance of our solar system’s own Kuiper Belt – the region occupied by Pluto, Eris, and thousands of smaller icy bodies.

In other words, if there were any cities on the edge of our solar system, we ought to be able to see them now. It’s doubtful there are cities on, say, Pluto. And all the stars – even the nearest ones – are no closer than 10,000 times Pluto’s distance from our sun. So we don’t have telescopes that could see city lights on planets surrounding those distant stars.

Image Credit: David A. Aguilar (CfA)

But future generations might spot them. As with other SETI (search for extraterrestrial life) methods, Loeb and Turner rely on the assumption that aliens would use Earth-like technologies. This is reasonable because any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness.

How easy would it be to spot a city on a distant planet? Clearly, this light will have to be distinguished from the glare from the parent star. Loeb and Turner suggest looking at the change in light from an exoplanet as it moves around its star.

As the planet orbits, it goes through phases similar to those of the Moon. When it’s in a dark phase, more artificial light from the night side would be visible from Earth than reflected light from the day side. So the total flux from a planet with city lighting will vary in a way that is measurably different from a planet that has no artificial lights.

Spotting this tiny signal would require future generations of telescopes. However, the technique could be tested closer to home, using objects at the edge of our solar system. Astronomers can hone the technique and be ready to apply it when the first Earth-sized worlds are found around distant stars in our galaxy. Turner said:

It’s very unlikely that there are alien cities on the edge of our solar system, but the principle of science is to find a method to check. Before Galileo, it was conventional wisdom that heavier objects fall faster than light objects, but he tested the belief and found they actually fall at the same rate.

Loeb and Turner’s work has been submitted to the journal Astrobiology and is available online.

Bottom line: Researchers Avi Loeb of Harvard-Smithsonian Center for Astrophysics and Edwin Turner of Princeton University suggest that the bright lights of cities, which are clearly visible on a planet even from space, might reveal the existence of alien life on other planets. The researchers say that today’s best telescopes ought to be able to see the light generated by a Tokyo-sized metropolis at the distance of the Kuiper Belt – the region occupied by Pluto, Eris, and thousands of smaller icy bodies.


The Best Equipment for Urban Stargazing

Photo credit: cho-web via Flickr

In addition to your eyes and layers to keep warm, there is some additional equipment you can bring when going urban stargazing to help make it a successful night.

Good Telescopes for Urban Stargazing

If you’re going to purchase a telescope for urban stargazing, there are some considerations to keep in mind:

  • The aperture of the telescope is the most important factor to help you choose a good telescope that will actually allow you to see things. A rough rule is that the larger the aperture, the more light your telescope can collect and show you. When you’re trying to view distant objects, bigger is better.
  • The length of a telescope does not correlate to its value. Many people start out with cheap, long telescopes that don’t do a great job of unlocking your view of the cosmos at all.
  • While there are smaller scopes, anything less than 70mm in diameter is not going to be powerful enough to do more than magnify what you can already see with your eyes. In the 80mm-90mm range, you’ll start to see more objects and also get a better view of the planets and stars.
  • When first starting out, expect to spend $100-$250 for a good starter telescope.

With that in mind, here are some telescope options:

BrandTelescopeDiameterPricePurchase
Celestron21061 AstroMaster 70AZ Refractor Telescope70mm$Click Here
OrionObserver 80ST Equatorial Refractor Telescope80mm$Click Here
Gskyer Telescope600x90mm AZ Astronomical Refractor Telescope90mm$$Click Here
Celestron21045 Equatorial PowerSeeker EQ Telescope114mm$Click Here
CelestronOmni XLT 150 Telescope150mm$$$Click Here

(Pricing: $ = <$100, $ = $100-$150, $$ = $150-$200, $$ = $200-$250, $$$ = $500+)

Best Stargazing Apps for Urban Stargazing

Using a stargazing app can be really helpful when you’re urban stargazing, as it will help you plan and understand what you might see – and help you spot exactly what you’re looking at once you’re stargazing. Note that it’s a pretty big faux pas to pull out your phone while stargazing, as phones produce a lot of light and mess with our night vision. So peek at your stargazing app in the car once you arrive, then just look at the wonders of the sky above.

  • Night Sky – This app uses augmented reality to allow you to see the night sky in any direction you point your phone, plus has information about every object you can see. There are some cool AR/VR paid purchase options too. Free, available in the Apple app store here.
  • SkyView® Lite – This app also uses AR to show you objects in the night sky, and has loads of information about everything you can see. Free, available in the Apple app store here. This app is called SkyView® Free in the Google Play store here.
  • Star Chart – Similar to other apps, this one uses AR to help you navigate the sky. Free, available in the Apple app store here and the Google Play store here.
  • SkySafari – Another AR app for viewing the night sky, this app also has a narrated tour of the sky you can purchase in-app. Free, available in the Apple app store here and the Google play store here.

Other Equipment You Might Need

Photo credit: Max Delaquis via Flickr

In addition to a telescope and a star map/app, there are a few other things that are helpful but not necessary for urban stargazing.

  • Red Lights – when you’re stargazing, you want to use red lights so your eyes aren’t affected and you can still see in the dark. There are some great, affordable hand-held flashlight options, including this clip-on one and this heavy-duty one, both less than $15.
  • Laser Pointer – A handheld green laser pointer can be great for pointing to specific stars (“which one? This one? No, that one!”) Sky & Telescope has a great article about laser pointers and when/how you should use them for stargazing. As a quick reminder: never look directly into the beam of light, and never shine your laser at people/animals, reflective signs/buildings, or airplanes.
  • Telescope Filters – If you really want to have the best experience possible, some telescope manufacturers make filters to help reduce light pollution at various wavelengths. Celestron, among others, offers a narrowband filter that can help you more easily spot distant deep space objects more easily.

If you still have questions or want to learn even more about urban stargazing, there’s also a great book Urban Astronomy: Stargazing from Town & Suburbsthat can teach you all you ever wanted to know. Have questions? Email us!

Featured photo credit: GlacierNPS via Flickr

Share this to help others enjoy the night sky!

Valerie Stimac

Valerie is the founder and editor of Space Tourism Guide. She decided to start the site after realizing how many friends and family had never seen the Milky Way, and that space tourism was going to unlock the next great travel destination: space!

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Will we soon see city lights glittering on distant planets?

Yesterday was day four of the Astrobiology Science Conference 2019 and the big news was NASA’s announcement that it will go ahead with the Dragonfly mission to explore Saturn’s moon Titan. The mission will launch in 2026 and arrive at Titan in 2034.

I watched the announcement on NASA TV with a few hundred others in the plenary ballroom at the conference hotel. A huge cheer went up as soon as Dragonfly was mentioned. Dragonfly was chosen over the proposed CAESAR comet sample-and-return mission and Dragonfly seemed the clear choice of the astrobiology community. This is not because CAESAR was uninteresting or unworthy, but because the idea of a drone flying around Saturn’s moon Titan, sampling the soil and atmosphere, was just too sweet and too romantic to resist. And space explorers are nothing if not romantic.

Now, on to the most exciting session I’ve attended so far – it was on Wednesday and was about “technosignatures.”

Astrobiologists are interested in signs of life – they call them “biosignatures” – and how these signs might arise and be detected in places like Mars, Titan and planets surrounding distant stars. I wrote about some of that in a previous blog from the conference.

Intelligent, advanced, and technologically capable

But what the public really want to see, according to one scientist here, are “technosignatures”. These are signs that intelligent, advanced, technologically capable beings exist (or existed) on another planet. Given the popularity of Star Wars, Star Trek and more recently, The Expanse, who could disagree?

Technosignatures could include evidence of megastructures – such as a Dyson sphere – surrounding a star or planet. (Hopefully you followed the saga of Tabby’s Star.) Other planetary technosignatures could include indications of artificial illumination (especially on the planet’s night side), or detection of waste heat from technological processes. Also fair game are urban heat islands, unusual shapes on the surface of a planet – perhaps like Dubai’s famous Palm Islands – or unusual albedo maps. And, of course, listening for electromagnetic signals from a planet, which is something the SETI community has been doing for years (albeit in a blunt fashion at relatively low bandwidth).

Some scientists here think that we are on the verge of being able to detect evidence of extraterrestrial technologies today, if they’re out there. Thomas Beatty, an astronomer at the University of Arizona, said “we are very close to detecting technosignatures from exoplanets” with today’s telescopes – or the next generation of instruments.

Bright lights, alien city

The proposed telescope LUVOIR could, he said, see nighttime lights (from cities) on an planet around Proxima Centauri, the closest star to Earth, only 4.3 light-years away in only 100 hours of observing time. Proxima Centauri is an M dwarf that has the exoplanet Proxima Centauri b in its habitable zone, where liquid water could exist. Svetlana Berdyugina at Albert-Ludwigs University of Freiburg in Germany talked about processing light signals to begin to distinguish potential large-scale land continents amidst an ocean background.

Imaging continents on other worlds. I don’t know about you, but that blows my mind. Check-out Berdyugina’s 2017 talk for more on this topic.

Other speakers want to use machine learning to pluck meaningful information from the immense streams of data that are, and increasingly will be, beamed back from scientific instruments and missions.

This has been one of the best, most interesting conferences I’ve ever attended in my 20 years as a science writer. Amidst all the talks and science, there has been a real sense of adventure, of pure curiosity wanting to know what is out there. The possibilities for this field seem almost endless, as large as the universe itself.

Dragonfly lands in 2034. What will come after that is being dreamed and discussed at conferences just like this one. I’m coming back next year.


Cyprus Astronomy Organisation

Believe it or not, this is the most asked question that astronomers encounter. Many people do not understand the difference. In ancient times, they were considered one and the same. But the two disciplines were separated during the Age of Reason in the 17th century. Astrology is a practice of using the locations of the planets to look into a person's personality or predict the future. It is not a science and is considered a form of divination. By contrast, astronomy is the scientific study of the universe. Astronomers observe the objects in the night sky to try to determine their composition and learn more about the origin and structure of the universe.

Question 2. Do I need an expensive telescope to enjoy astronomy?

Many people hesitate to get involved with astronomy because they believe it requires expensive equipment. The only thing you really need to enjoy the night sky is your eyes, a dark viewing location, and some patience. To get a better look at things, a pair of binoculars can provide a really good view. Many people will be surprised how many more stars and objects they can see with a decent pair of 10X binoculars. They collect much more light than the human eye and will bring much dimmer objects into view. You can even see Jupiter’s moons with binoculars. A simple camera tripod to steady the binoculars is also a good idea, since your arms can get tired very quickly.

Question 3. Why can't I see very many stars at night?

If you live near a big city, you may not be able to see a lot of stars. The reason for this is light pollution. Dust and water vapor in the atmosphere reflects the bright city lights back down towards the ground. This “light pollution” tends to be brighter than some of the dim stars and other deep sky objects, essentially hiding them from view. To truly appreciate the night sky, you must get as far away from city lights as possible. There is no more beautiful sight then the band of the Milky Way stretching across a dark sky. We can all help to combat light pollution by convincing our local authorities to use more efficient light fixtures that shine the light on the ground and block it from going up into the sky.

Question 4. How does a telescope work?

The primary purposes of a telescope are to gather light and magnify an image. The aperture (opening) of a telescope is larger than that of the human eye and therefore, can gather much more light. This enables us to see dim objects that are too faint to see with the naked eye. The larger the aperture of the telescope, the more light it can gather. Telescopes also use a series of lenses and/or mirrors to magnify the image, enabling us to see more detail.

Question 5. What is the speed of light?

Light travels at a constant speed of 186,262 miles per second (299,792,458 meters per second). Since the speed of light is constant, it can also be used to measure vast distances. Distances between objects in space are measured in light years. One light year is equal to the distance light travels in a year, which is just under 6 trillion miles (10 trillion kilometers). The speed of light is considered to be the ultimate speed limit in the universe. Scientists believe that it is impossible to travel faster than light because any object traveling at the speed of light would have to achieve infinite mass.

Question 6. How far is the Moon from Earth?

The distance between the Moon and the Earth averages 238,857 miles (384,403 kilometers). Since the Moon’s orbit is not a perfect circle, its distance varies. At its farthest point, known as apogee, it is 252,080 miles (405,686 km) away. At its closest point, known as perigee, it is 225,621 miles (363,104 km) away.

Question 7. How was the Moon formed?

Astronomers believe that the Moon was formed billions of years ago when a small planet the size of Mars collided with the Earth. The foreign planet hit with a glancing blow and ejected a large part of the Earth’s molten mantle into space. Over time, this material coalesced and cooled to form the Moon.

Question 8. Why is the Moon larger when it is close to the horizon?

Although the Moon looks much larger when it is low in the sky near the horizon, this is actually just an optical illusion. It is actually the same size as when it is directly over head. This illusion has been known since ancient times and also happens with the Sun and the constellations. This same illusion works on mountains and tall buildings as well. They appear larger at long distances than they do at closer distances. The reasons for this are complex, but they have something to do with how our brains interpret the sizes of large objects on the horizon. If you don't believe this is only an illusion, you can compare the size of the Moon near the horizon to the size directly over head by holding your finger out at arm's length and comparing the sizes of the Moon with your finger.

Question 9. Can you see the flag on the Moon with a telescope?

This is a question that astronomers get asked a lot. Unfortunately, the equipment left behind by the Apollo missions is tiny in comparison to the size of the Moon. Ground-based telescopes, especially those owned by amateur observers, are not capable of resolving objects this small at such extreme distances. Extremely large telescopes could theoretically catch a bright spot of sunlight reflecting from some of the moon landing equipment, although they would not be able to observe the equipment directly.

Question 10. How far away is the Sun?

The average distance from the Sun to the Earth is 93 million miles (149 million kilometers). Because the Earth’s orbit around the Sun is not a perfect circle, it varies. At its closest point to the Sun, known as perihelion, the distance is 91 million miles (146 million km). At is farthest point, known as aphelion, the distance is 94.5 million miles (152 million km).

Question 11. How big is the Sun?

The Sun is an average-sized star that is 865,000 miles (1,392,000 kilometers) in diameter. It is so large that you could fit the planet Earth inside it well over a million times. The Sun actually makes up about 99% of the entire mass of the Solar System. The remaining objects, including all of the planets, moons, comets, and asteroids compose the other 1% of the Solar System.

Question 12. How hot is the Sun?

The core of the Sun is extremely hot at about 27 million degrees Fahrenheit (15 million degrees Celsius). The surface of the Sun is much cooler than the core, at about 9,900 degrees F (5,500 degrees C). For some strange reason, not yet completely understood by scientists, the Sun’s outer atmosphere is hotter than its surface. Known as the corona, its temperature reaches 5 million degrees F (2.7 million degrees C).

Question 13. How long does it take the light from the Sun to reach Earth?

The light from the Sun travels at the speed of light, 186,282 miles per second. Since the Sun is about 93 million miles from Earth, it takes the light about 8.4 minutes to reach us. This means that when you look up at the Sun, you are actually seeing it the way it looked 8.4 minutes ago. To give you an idea just how close we are to the Sun, the light from the next nearest star, Proxima Centauri, takes 4.3 years to reach the Earth.


Watch for false dawn or dusk

Photo above: Yuri Beletsky in Chile caught the zodiacal light in the evening around this time last year, on September 10, 2018. In this image, the Milky Way stretches across the sky, while zodiacal light can be seen as the faint pyramid-shaped light toward the bottom of the image. The 2 bright planets within the zodiacal light in this image are Venus (closest to horizon) and Jupiter.

The September equinox came on September 23, 2019, and the moon is new on October 28. That combination makes these next few weeks ideal for seeing the zodiacal light, also known as the false dawn. If you’re in the Northern Hemisphere, look east, about an hour before the light of true dawn.

Southern Hemisphere? Your spring equinox was September 23, and the moon phase, of course, is the same for all of us. But you’re more likely to see zodiacal light in the evening now, as Yuri Beletsky did (see photo, top of post). Look west about an hour after the sun goes down.

You need a dark sky location to see the zodiacal light, someplace where city lights aren’t obscuring the natural lights in the sky. The zodiacal light is a pyramid-shaped glow in the east before dawn (or after twilight ends in the evening). It’s even “milkier” in appearance than the starlit trail of the summer Milky Way.

From the Northern Hemisphere now, the zodiacal light can be seen for up to an hour or so before true dawn begins to break. Look for it about 120 to 80 minutes before sunrise. It also lingers that long after evening twilight ends. Unlike true dawn or dusk, though, there’s no rosy color to the zodiacal light.

View larger. Ken Christison of North Carolina, USA, caught the zodiacal light (false dawn) on October 28, 2019, at 6:23 a.m. EDT. Because Regulus, the brightest star in the constellation Leo the Lion, sits almost exactly on the ecliptic (center line of the zodiac), the tip of this cone of light points right at the bright star Regulus. Thank you Ken!

The reddish skies at dawn and dusk are caused by Earth’s atmosphere, and the zodiacal light originates far outside our atmosphere. When you see the zodiacal light, you are looking edgewise into our own solar system. The zodiacal light is actually sunlight reflecting off dust particles that move in the same plane as Earth and the other planets orbiting our sun.

This light can be noticeable and easy to see from latitudes relatively close to Earth’s equator – for example, like those in the southern U.S. You might see it while driving a lonely highway far from city lights, mistaking the zodiacal light for the lights of a city or town just over your horizon.

Meanwhile, skywatchers in the northern U.S. or Canada sometimes say wistfully that they’ve never seen it, although in recent years we’ve seen many photographs of the zodiacal light taken from those northerly latitudes.

Here’s the evening zodiacal light in March as captured on film in Canada. This wonderful capture is from Robert Ede in Invermere, British Columbia.

Bottom line: People in the Northern Hemisphere can look for the zodiacal light in the east before dawn now. People in the Southern Hemisphere can look west after sunset.