# How do scientists know there are about 300 billion stars in a galaxy and there are about 100 billion galaxies?

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Just to think about this is mind boggling. But how do scientist get these numbers? What technology/system/theory do they they use?

It's a matter of statistics.

Scientists take a small amount of the space (let's say 1 second of arc). They look at it carefully with strong telescopes, and count all the stars and galaxies they see. Then, they extrapolate that number at the total visible space.

Of course they can compute several spots of the space and make an average count.

Since the number is extrapolated, that's why it doesn't really matter if it is 100 billion or 300 billion of stars. The goal is to have an order of magnitude as pointed by Moriarty.

The way it works is as follows. We do detailed studies of stars in the solar neighbourhood. This establishes the local density of stars and the mix of masses they possess (called the stellar mass function). We compare that with the mass function of clusters of stars and note that to first order it appears invariant.

We can then triangulate the problem in various ways: we can make a model for the stellar density of the Galaxy, assume it all has the same mass function and hence get a number of stars. The model may be based on crude light-to-mass conversions, but more often would be based on deep surveys of the sky - either narrow pencil beam surveys from HST, or broader surveys like SDSS, The key is to be able to count stars but also estimate how far away they are. This is highly uncertain and relies on some assumptions about symmetry to cover regions of our Galaxy we cannot probe.

Another method is to count up bright objects that might act as tracers of the underlying stellar population (eg red giants), compare that with the number of giants in our well-studied locale, and from this extrapolate to a total number of stars, again relying on symmetry arguments for those bits of the Galaxy that are distant or obscured by dust.

A third way is to ask, how many stars have lived and died in order to enrich the interstellar medium with heavy elements (a.k.a. metals). For example, it turns out there must have been about a billion core-collapse supernovae to create all the oxygen we see. If we assume the mass function is invariant with time and that supernovae arise from stars above 8 solar masses, then we also know how many long-lived low-mass stars were born with their high-mass siblings and hence estimate how many stars exist today.

The number, whether it be 100 billion or 300 billion is no more accurate than a factor of a few, but probably more accurate than an order of magnitude. The main issue is that the most common stars in the Galaxy are faint M dwarfs,that contribute very little light or mass to the Galaxy, so we really are relying on an extrapolation of our local knowledge of these objects.

The number of galaxies problem is easier, though the number is less well defined. We assume that on large scales the universe is homogeneous and isotropic. We count up how many galaxies we can see in a particular area, multiply it up to cover the whole sky. The number must then be corrected for distant faint galaxies that cannot be seen. The difficult here is that we are looking into the past and the number of galaxies may not be conserved, either through evolution or mergers. So we have to try and come up with a statement like "there are n galaxies in the observable universe today that are more luminous than L". I think this number is certainly only an order of magnitude estimate.

## SEXTILLION STARS

WASHINGTON – A new study reveals that there are 300 sextillion stars in the universe. Three times more than previously calculated.

Sextillion. That’s a 23 zeros. A trillion times 100 billion.

The estimate, contained in a study published online Wednesday in the journal Nature, is based on findings that there are many more red dwarf stars the most common star in the universe than once thought.

Astronomers have been counting and re-counting the stars for the last five years – much like the Bush-Gore election results.

The study by Yale University astronomer Pieter van Dokkum and Harvard astrophysicist Charlie Conroy questions a key assumption that astronomers often use: that most galaxies have the same properties as our Milky Way . And that conclusion is deeply unsettling to astronomers who want a more orderly cosmos.

When scientists previously estimated the total number of stars, they assumed that all galaxies had the same ratio of dwarf stars as the Milky Way, which is spiral-shaped. Much of our understanding of the universe is based on observations made inside our own galaxy and then extrapolated to other galaxies.

But about one-third of the galaxies in the universe are elliptical, not spiral, and van Dokkum found they aren’t really made up the same way as ours.

Using the Keck telescope in Hawaii, van Dokkum and a colleague gazed into eight distant, elliptical galaxies and looked at their hard-to-differentiate light signatures. The scientists calculated that elliptical galaxies have more red dwarf stars than predicted. A lot more.

“We’re seeing 10 or 20 times more stars than we expected,” van Dokkum said. He then had his associates literally count the stars – one by one.

Generally scientists believe there are 100 billion to a trillion galaxies in the universe. And each galaxy — the Milky Way included — was thought to have 100 billion to a trillion stars. Sagan, the Cornell University scientist and best-selling author who was often impersonated by comedians as saying “billions and billions,” usually said there were 100 billion galaxies, each with 100 billion stars.

Van Dokkum’s work takes these numbers and adjusts them. That’s because some of those galaxies the elliptical ones, which account for about a third of all galaxies â€” have as many as 1 trillion to 10 trillion stars, not a measly 100 billion. When van Dokkum and Conroy crunched the incredibly big numbers, they found that it tripled the estimate of stars in the universe from 100 sextillion to 300 sextillion.

That’s a huge number to grasp, even for astronomers who are used to dealing in light years and trillions, Conroy said.

“It’s fun because it gets you thinking about these large numbers,” Conroy said. Conroy looked up how many cells are in the average human body — 50 trillion or so — and multiplied that by the 6 billion people on Earth. And he came up with about 300 sextillion.

So the number of stars in the universe “is equal to all the cells in the humans on Earth” a kind of funny coincidence, Conroy said.

For the past month, astronomers have been buzzing about van Dokkum’s findings, and many aren’t too happy about them, said astronomer Richard Ellis of the California Institute of Technology .

Van Dokkum’s paper challenges the assumption of “a more orderly universe” and gives credence to “the idea that the universe is more complicated than we think,” Ellis said. “It’s a little alarmist.”

Ellis said it is too early to tell if van Dokkum is right or wrong, but his work is shaking up the field “like a cat among pigeons.”

Astronomers on both sides of the “sextillion” issue are back to counting stars. They are all eager to come up with the EXACT number of stars in the universe.

Van Dokkum agreed, saying, “Frankly, it’s a big pain.”

Ellis said the new study does make sense. Its biggest weakness might be the assumption that the chemical composition of dwarf stars is the same in elliptical galaxies as in the Milky Way. That might be wrong, Ellis said. If it is, it would mean there are only five times more red dwarf stars in elliptical galaxies than previously thought, instead of 10 or 20, van Dokkum said.

## What four close planets can see us?

The four stars with confirmed exoplanets located within 100 light-years of the Sun include some exciting exoplanets.

Ross 128 b, the second-closest temperate exoplanet to us and the nearest exoplanet around a quiet red dwarf star. Now even surer to be a prime target for the James Webb Space telescope and the ESO’s Extremely Large Telescope, which will be able to search for biomarkers in the planet’s atmosphere.

### What we know about Ross 128 b

• What: an Earth-mass exoplanet around a red dwarf star
• Where: 11 light-years away in the constellation of Virgo (13th closest star system to the Sun)
• In Earth Transit Zone: 2,158 years (from 3,057 until 900 years ago)

### What we know about Teegarden’s Star

• What: two Earth-mass exoplanets in the habitable zone of a red dwarf star
• Where: 12 light-years away in the constellation of Aries (25th closest star system to the Sun)
• In Earth Transit Zone: Will enter in 29 years for 410 years.

### What we know about GJ9066

• What: two giant planets orbiting a red dwarf star
• Where: 15 light-years away in the constellation of Cetus
• In Earth Transit Zone: will enter the ETZ in 846 years and remain in it for 932 years.

### What we know about the Trappist-1 system

• What: Seven temperate rocky planets orbiting an ultra-cool red dwarf star, four in the habitable zone
• Where: 40 light-years away in the constellation of Aquarius
• In Earth Transit Zone: Will enter the ETZ in 1,642 years and remain there for 2,371 years.

Extended sample of the full machine-readable table of ETZ stars, sorted by distance from the Sun . [+] from the article “Past, present and future stars that can see Earth as a transiting exoplanet”, by L. Kaltenegger & J. K. Faherty, Nature

L. Kaltenegger & J. K. Faherty, Nature

## How do we know that distant galaxies are composed of matter rather than anti-matter? If equal quantities of each were produced in the big bang, might not some parts of the universe contain primarily matter and other parts primarily anti-matter?

"When matter and antimatter meet, they annihilate each other and the mass is converted into energy--specifically, into gamma-rays. If a distant galaxy were made of antimatter, it would constantly be producing gamma-rays as it encountered the matter in the intergalactic gas clouds that exist throughout galaxy clusters.

"We do not see any steady stream of gamma-rays coming from any source in the sky. Therefore, astronomers conclude that there are not occasional 'rogue' galaxies made of antimatter. If there is any large amount of antimatter in the universe, it must encompass at least an entire galaxy cluster, and probably a supercluster. Once might postulate the existence of such antimatter superclusters, but then one would be faced with the problem of coming up with a mechanism that, shortly after the big bang, would have separated these now-gigantic clumps of antimatter from the neighboring clumps of mater. No such mechanism has yet been envisioned."

>Scott Dodelson is a scientist in the Theoretical Astrophysics Group at Fermi National Accelerator Laboratory. He offers a more detailed reply:

"The question of whether or not there is anti-matter in the universe has been around ever since the prediction of the existence of the anti-proton early this century. For reasons that I'll explain, most physicists don't believe there is much anti-matter around. But the fact that the question is still being asked (by many scientists) indicates that it has not been definitively answered. We may all be in for a big surprise!

"With that background, here is an overview of our present thinking. A simple way to test and see if there is anti-matter around is to send out a 'detector.' In this case, it is completely trivial to make a detector: it simply has to be made of matter! Any time matter collides with anti-matter, the two annihilate and produce lots of gamma rays. We have sent spacecraft to Jupiter and other planets. These objects didn't annihilate, so we know that our solar system does not contain much anti-matter.

"In fact, we can make a much stronger statement about the abundance of anti-matter by searching for gamma rays from other galaxies and clusters of galaxies. A typical cluster does not emit many gamma rays, so all the galaxies in it must be made solely of matter. It is possible that all the galaxies in a given cluster are made of matter while all those in another are made solely of anti-matter. If this were true, then there would be immense gamma radiation coming from the boundary regions between clusters of different types. At present, such radiation is not observed, a fact that again argues against this separation. Matter and anti-matter therefore must be separated on scales larger than cluster sizes (roughly ten million light years).

"There is a strong argument against the possibility that matter and anti-matter exist in equal numbers in our universe but are for some reason separated. This argument goes back to the early universe and asks, When must the matter and anti-matter have been separated? It must have been very early, when the temperature of the universe was roughly 500 billion Kelvins. If they hadn't separated by then, matter and anti-matter would have mutually annihilated, because the universe was very dense. Is it possible to think of a mechanism that separated matter from anti-matter when the universe was very hot and dense? Apparently not, for any way of separating them has to obey causality. Early in the history of the universe, when annihilation between matter and anti-matter was occurring, the farthest possible distances that were in causal contact with each other were about 100 kilometers. This size is a billion times smaller than the regions that would grow to be clusters. So it seems impossible that matter was separated from anti-matter on scales the size of clusters today. The most natural explanation is that the universe is made up only of matter and contains no large reservoir of anti-matter. In fact, there are theories which explain how such an asymmetry could have occurred.

"Having said all this, I want to reiterate that this is not the final word. The arguments I have presented are suggestive but not compelling. For this reason, some physicists are excited about the Alpha Magnetic Spectrometer, a device that the National Aeronautics and Space Administration wants to fly in the Earth's orbit that will look directly for anti-matter."

## Yes, There Is Life in Space—Deal With It

N o one has ever discovered life in space, and given the enormity of the universe and our tiny, modest place in it, it’s entirely possible no one will&mdasheither in our lifetimes or for many lifetimes to come. But never mind, because life is out there&mdashindeed, it’s everywhere, simply because chemically and mathematically it has to be there.

That’s increasingly the view of investigators studying the science of exobiology&mdashalso known as astrobiology, also known as just plain ET. There’s good reason for that kind of investigatory optimism. Water, we now know, is everywhere in the cosmos, on planets and moons, in the matrix of asteroids, swirling through interstellar space itself. Hydrocarbons&mdashthe basic molecular stuff of life&mdashare ubiquitous too, as are more complex amino acids.

And while we once knew of only the eight planets in our own solar system, in just the past 20 years, scientists have discovered thousands more orbiting other stars in our galaxy. Our sun is just one of those 300 billion stars, and there are perhaps 100 billion more galaxies in the universe. That’s not a sample group of infinity, but it’s a huge one all the same. If biological chemistry is everywhere and the planets on which it could play out are as well, there’s little reason to believe the magic would happen only on Earth.

&ldquoThe universe is hardwired to be an organic chemist,&rdquo Scott Sandford, an astrobiologist at the NASA Ames Research Center near Silicon Valley, told me for a story in a recent issue of TIME. &ldquoIt&rsquos not a very clean or tidy one, but it has really big beakers and plenty of time.&rdquo

Not everyone agrees with that view, but like it or not, it’s becoming&mdashif it hasn’t already become&mdashthe majority position.

What do you think? Weigh in on Twitter with your thoughts and questions and I’ll discuss them on the next episode of my new Time podcast, It’s Your Universe, (available on iTunes and Stitcher), which each week takes you on a tour of a new destination in our solar system. We’ve so far visited Mercury, Venus, Earth, Mars, and Jupiter. On Thursday, March 10, we’ll stop and consider the case for life in the cosmos at large.

## Kepler’s Universe: More Planets in Our Galaxy Than Stars

Astronomers estimate that the Milky Way contains up to 400 billion stars and thanks to the Kepler mission, we can now estimate that every star in our galaxy has on average 1.6 planets in orbit around it.

This new video from our friends Tony Darnell and Scott Lewis focuses on the discoveries that the Kepler Space Telescope has made, which has opened up a whole new universe and a new way of looking at stars as potential homes for other planets. Only about 20 years ago, we didn’t know if there were any other planets around any other stars besides our own. But now we know we live in a galaxy that contains more planets than stars.

If you extrapolate that number to the rest of the Universe, it’s mind-blowing. According to astronomers, there are probably more than 170 billion galaxies in the observable Universe, stretching out into a region of space 13.8 billion light-years away from us in all directions.

And so, if you multiply the number of stars in our galaxy by the number of galaxies in the Universe, you get approximately 10 24 stars. That’s a 1 followed by twenty-four zeros, or a septillion stars.

However, it’s been calculated that the observable Universe is a bubble of space 47 billion years in all directions… or it could be much bigger, possibly infinite. It’s just that we can’t detect those stars because they’re outside the observable Universe.

So, there’s a lot of stars out there.

As the video says, space telescopes give us “a glimpse of our humble place in the cosmic ocean.”

## In a distant galaxy, scientists find oldest oxygen in universe and stars from edge of cosmic dawn

Star formation in the very distant galaxy MACS1149-JD1 started at an unexpectedly early stage, only 250 million years after the Big Bang. This discovery also represents the most distant oxygen ever detected in the Universe. (Credit: ESO)

In a distant galaxy more than 13 billion light-years from Earth, astronomers have discovered traces of the oldest known oxygen in the universe, as well as evidence that ancient stars “turned on” as early as 250 million years after the Big Bang.

These findings, published Wednesday in Nature, suggest that star formation at the dawn of the cosmos may have been more common and robust than previously thought.

“It is not surprising that stars began to form at about that time, but what is surprising is that we found most of the stars in this galaxy were born so early,” said Richard Ellis, an astrophysicist at the University College of London who contributed to the study.

“Most models suggest star formation begins gradually, not in such a single burst of activity,” he added.

The ancient galaxy, known as MACS1149-JD1, was discovered in 2012, but scientists didn’t know how far away — and thus, approximately how old — it was until now.

To get an accurate measurement of its distance from Earth, an international team of astronomers used the ALMA telescope in the Chilean desert to look for the signature of ionized oxygen within the light emanating from the galaxy.

“ALMA is a very sensitive observatory, and oxygen is one of the most readily detected spectrum lines in hot gas,” Ellis said.

Zoom into the early Universe to the faint galaxy MACS1149-JD1, where stars began only 250 million years after the Big Bang. (Credit: ESO, ALMA (ESO/NAOJ/NRAO), N. Risinger, skysurvey.org)

Because the universe is expanding, the spectrum line associated with the oxygen was stretched out as it traveled through space in a process known as redshift.

By measuring its wavelength once it reached Earth, scientists were able to get a remarkably accurate picture of how long this light has been beaming across the cosmos.

The oxygen line from MACS1149-JD1 originally was emitted at a wavelength of about 88 microns, but by the time it reached ALMA, it had stretched to about 893 microns, said Takuya Hashimoto, an astronomer at Osaka Sangyo University and the National Astronomical Observatory of Japan who led the study.

That indicates that the light from this galaxy was emitted 13.28 billion years ago, when the universe was about 550 million years old, he said.

But that’s just part of the story.

Immediately after the Big Bang, there was no oxygen in the universe. That’s because oxygen can be forged only in the nuclear furnace of stars. And it is released into the cosmos only when those stars die.

Therefore, the presence of oxygen in the MACS1149-JD1 galaxy suggests that by 500 million years after the Big Bang, this galaxy already had reached a certain level of chemical maturity. Stars had already died there.

To get a more accurate picture of how old the galaxy was when it was emitting light 13.28 billion years ago, the astronomy team studied its color with the help of the Hubble and Spitzer space telescopes.

“The redder the galaxy, the older the stellar population,” said study coauthor Nicolas Laporte, a researcher at University College London. “And in our case, we have a very red galaxy, which is due to old stars.”

Indeed, these measurements allowed the scientists to determine that many of the stars in MACS1149-JD1 were already 300 million years old 13.28 billion years ago. This means they had to have formed about 250 million years after the Big Bang — when the universe was just 2% its present age.

As usual, these new discoveries have led researchers to ask more questions.

For example, are there many galaxies in the universe as old as this one, or is this an extra-old outlier?

Ellis said the team already has plans to observe two additional distant galaxies to determine their ages. Perhaps one, or both, of them will be of a similar vintage.

Hashimoto added that when the James Webb Space Telescope comes online around 2020, it is likely that many more distant galaxies will be discovered.

Also, if stars were turning on en masse 250 million years after the Big Bang, then how early in the universe’s history did the first stars light up the darkness of space?

“The mature stellar population in MACS1149-JD1 implies that stars were forming back to even earlier times, beyond what we can currently see with our telescopes,” Laporte said. “This has very exciting implications for finding ‘cosmic dawn’ when the first galaxies emerged.”

Do you love science? I do! Follow me @DeborahNetburn and “like” Los Angeles Times Science & Health on Facebook.

## Quick Question: How Many Galaxies Are There?

For hundreds of thousands of years, humanity has peered up at the night sky with one question top of mind: what else is out there?

There's the moon (8), of course, and then the sun. And as our view of the night sky has come into sharper focus, we've discovered other objects, too, like the seven other planets that orbit the sun and their many moons. We spotted comets and asteroids, black holes and galaxies, packed full of millions of stars. On especially dark nights, you can even spot the edges of our own Milky Way galaxy.

So exactly how many galaxies are out there? Current estimates suggest there may be as many as 2 trillion&mdashthat's trillion with a T&mdash galaxies in the observable universe.

Each galaxy has its own unique set of features and characteristics. Over the course of millions of years, they form gases, dust, stars, planets and moons. At the center of most galaxies lies a supermassive black hole, which tugs at nearby stars.

Famed astronomer Edwin Hubble became the first to devise a galactic classification system for the celestial features in 1926. According to his (very simplified) classification, there are five main types of galaxies: spiral, barred spiral (the Milky Way is a barred spiral), lenticular, elliptical, and irregular.

### Intergalactic Arithmetic

Only in recent years have we been able to estimate and understand how much else there is in the universe. Scientists use telescopes like the Earth-orbiting Hubble Space Telescope and Chandra X-ray Observatory and the European Southern Observatory's Earth-based Very Large Telescope to carry out galactic surveys and identify how many galaxies are in a patch of the sky the size of a pinhead held at arm's length.

Counting galaxies is kind of like playing a cosmic game of Where's Waldo. Astronomers are tasked with counting every galaxy they can find within that tiny sliver of space and then extrapolate it out across the entire sky.

Carving a fraction out of the sky and identifying all of the galaxies in it across the broad spectrum of wavelengths is not an easy task. You have to fight through dust and other matter that may dampen a galaxy&rsquos light. And it takes a long time for Hubble and other telescopes to take these images and stitch them together.

There are undoubtedly galaxies that we can&rsquot even see. Because our universe is expanding, some extremely distant and old galaxies, which formed shortly after the big bang, are zooming away from us faster than the speed of light. It&rsquos virtually impossible to spot them with current technology.

### Hubble Goes Deep

We largely have the Hubble Space Telescope to thank for illuminating our place in the universe. When it isn't chasing comets or counting planetary rings, Hubble periodically snaps detailed pictures of tiny slices of the sky. Hubble released the first Deep Field survey in 1995.

"We were trying to find sort of an indiscriminate area of the sky where no observation had been made before," Robert Williams, the former director of the Space Telescope Science Institute, told Vox in 2016. The image revolutionized astronomy. From the glittering image, astronomers spotted about 1,500 glittering galaxies. Subsequent images revealed even more.

In 2012, Hubble&rsquos eXtreme Deep Field image was released. Over the course of ten years, the telescope had snapped images of a tiny patch of sky for a total of 50 days. It revealed a slice of sky&mdashabout one thirty-two millionth of the sky, to be exact&mdashscattered with twinkling galaxies of all shapes and sizes. Using this new image, astronomers estimated that there may be 100 to 200 billion galaxies in the observable universe.

But just four years later, a team of researchers from the University of Nottingham reanalyzed Hubble&rsquos images and assessed data from other observatories, pulling our universe-wide galaxy count up by a factor of 10 to 2 trillion. The astronomers published their new numbers in the Astrophysical Journal.

&ldquoIt boggles the mind that over 90 percent of the galaxies in the [observable] Universe have yet to be studied,&rdquo astrophysicist Christopher Conselice of the University of Nottingham in the UK told the Atlantic at the time. &ldquoWho knows what interesting properties we will find when we discover these galaxies with future generations of telescopes?&rdquo

### Next Generation Estimates

In a sense, we&rsquore playing a game of cat and mouse with the universe. We&rsquore scrambling to develop instruments powerful enough to catch sight of galaxies that are zipping away from us at break-neck speeds. The upcoming James Webb Space Telescope is slated to take Hubble&rsquos reins as the preeminent galaxy spotting space telescope.

The infrared observatory is 100 times more powerful than Hubble and will have the ability to probe the cosmos in greater detail than ever before, spotting distant galaxies too faint for every previous generation of telescopes to see. Astronomers hope to view galaxies that formed just after the Big Bang, roughly 13.5 billion years ago. It'll give us the closest look yet to the beginning of everything.

## Helen Maynard-Casely, planetary scientist:

I'm of the opinion that it's only a matter of time before we find something that resembles biology somewhere other than on Earth. This is because we're increasingly finding various potential pockets in our solar system that may be hospitable to life as we know it.

For instance, consider the under-ice oceans of Europa and Ganymede (two of Jupiter's large moons): these are places where the temperature is just right, there is access to water and to minerals, too. Then again, that's viewing things with a very Earth-like lens, and of course alien life could be very different to our own.

That's why I'm really excited about further exploration of Saturn's moon Titan. Titan has a whole range of interesting molecules on its surface, as well as active weather systems to transport them about – this too, all within our solar system. And we know there are other solar systems within our galaxy.

Considering all of the above, it really does feel more and more inevitable that we will find a niche for some active biology somewhere. Whether it can say hello to us? Well, that's a different question.

## How do scientists know there are about 300 billion stars in a galaxy and there are about 100 billion galaxies? - Astronomy

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##### 10 Crazy Facts You Didn't Know About Space

There is so much about space, our solar system, and the galaxy that we still don't know! Space is vast. With billions of galaxies and stars, and planets in our own solar system yet to be fully explored or understood, scientists' knowledge of space is always evolving. There are, however, some really cool things we know about space right now! We've compiled a list of what we think are ten stellar facts that we hope you'll think are out of this world!

1. SPACE IS COMPLETELY SILENT

There is no atmosphere in space, which means that sound has no medium or way to travel to be heard.

2. THE HOTTEST PLANET IN OUR SOLAR SYSTEM IS 450° C.

Venus is the hottest planet in the solar system and has an average surface temperature of around 450° C. Did you know that Venus isn't the closest planet to the sun? That is Mercury. You would think that Mercury would then be the hottest, but Mercury has no atmosphere (which regulates temperature), resulting in big fluctuations.

3. A FULL NASA SPACE SUIT COSTS $12,000,000. While the entire suit costs a cool$12m, 70% of that cost is for the backpack and control module. However, the space suits that NASA uses were built in 1974. If these were priced by today's pricing, they would cost an estimated 150 million dollars!

4. THE SUN’S MASS TAKES UP 99.86% OF THE SOLAR SYSTEM.

The Sun accounts for 99.86% of the mass in our solar system with a mass of around 330,000 times that of Earth. Did you know that the Sun is made up of mostly hydrogen (three quarters worth) with the rest of its mass attributed to helium. If the Sun had a voice would it be high and squeaky from all that helium?

5. ONE MILLION EARTHS CAN FIT INSIDE THE SUN

The Sun is large enough that approximately 1.3 million Earths could fit inside (if squashed in) or if the Earths retained their spherical shape then 960,000 would fit. But can you visualise that number of Earths?

6. THERE ARE MORE TREES ON EARTH THAN STARS IN THE MILKY WAY

There are about three trillion trees on Planet Earth, and between 100-400 billion stars, approximately, in the galaxy.

7. THE SUNSET ON MARS APPEARS BLUE
Just as colors are made more dramatic in sunsets on Earth, sunsets on Mars, according to NASA, would appear bluish to human observers watching from the red planet. Fine dust makes the blue near the Sun's part of the sky much more visibilke, while normal daylight makes the Red Planet's familiar rusty dust color the most perceptible to the human eye.

8. THERE ARE MORE STARS IN THE UNIVERSE THAN GRAINS OF SANDS ON EARTH
The universe extends far beyond our own galaxy, The Milky Way, which is why scientists can only estimate how many stars are in space. However, scientists estimate the universe contains approximately 1,000,000,000,000,000,000,000,000 stars, or a septillion. While no one can actually count every single grain of sand on the earth, the estimated total from researchers at the University of Hawaii, is somewhere around seven quintillion, five hundred quadrillion grains. That is an awfully big sand castle!

9. ONE DAY ON VENUS IS LONGER THAN ONE YEAR.
Venus has a slow axis rotation which takes 243 Earth days to complete its day. The orbit of Venus around the Sun is 225 Earth days, making a year on Venus 18 days less than a day on Venus.

10. THERE IS A PLANET MADE OF DIAMONDS
There’s a planet made of diamonds twice the size of earth The "super earth," aka 55 Cancri e, is most likely covered in graphite and diamond. Paying a visit to that planet would probably pay for the \$12 million dollar space suit needed to get there!

Do you have a little one that loves learning about the planets?

Check out our Space Activity Book, and for more fun space-themed activities follow us on Pinterest!