This week we read, Papi, How Many Stars are in the Sky? and learned the words stars, sky, clear, and lullaby. Ask your child what each word means, and if they don’t know, explain the meaning to them or show them an example. Here are easy definitions to use.
Stars are the bright lights that we in the nighttime sky. Ask your child where in the sky the stars are. See if you can see any stars on a clear night.
The sky is up above.
Clear means that there are no clouds. If something is clear you can see right through it.
Mother singing a lullaby
A lullaby is a sweet song you sing to a baby or child to put them to sleep. Sing Rock-a-by-baby or another a favorite lullaby with your child at bedtime.
Can we see stars outside our Milky Way?
Photo at top of post by Jeff Dai in Tibet. Read more about this image.
One of you wrote:
Are there any stars outside our own galaxy that we can see with just the eye?
The answer is no – unless you count seeing the combined light of many billions of stars. From the Northern Hemisphere, the only galaxy outside our Milky Way that’s easily visible to the eye is the great galaxy in the constellation Andromeda, also known as M31. More about the Andromeda galaxy at the bottom of this post.
From the Southern Hemisphere, it’s possible to see two dwarf galaxies, the Large and Small Magellanic Clouds.
So what are we seeing when we look up? The image at the top of this post shows a hazy band in the sky. This is the edgewise view into our own Milky Way galaxy.
Our galaxy is about 100,000 light-years in a diameter, but it’s relatively flat, only about 10,000 light-years thick.
So – if we’re looking in a dark sky – when we look toward the galactic disk, we see the starry band of the Milky Way.
And when we look up or down – away from the flat disk of the galaxy – we’re also seeing Milky Way stars. All of the stars we see with the eye alone belong to our Milky Way galaxy.
EarthSky astronomy kits are perfect for beginners. Order today from the EarthSky store
View larger. Anthony Lynch Photography provided this beauty of photo in August, 2015. It’s a colorful Perseid meteor and the Andromeda galaxy. Thank you Anthony!
It is possible to see the Andromeda galaxy with the eye alone,
How Many Stars Are in the Universe?
The current night sky is dominated by the white glow of myriad middle-aged stars along the lane of the Milky Way. Interstellar “pollution” from thick dust lanes can be seen threading through the long band of stars. They are interspersed with a few pinkish emission nebulae from ongoing star formation. Thousands of stars appear as pinpoints of light throughout the sky.
(Image: © NASA, ESA, and Z. Levay (STScI/AURA))
Editor's Note: This story was updated at 12:20 p.m. E.S.T. on Thursday, May 24, 2018
The night sky is littered with twinkling lights, evidence that we are just one small planet circling one tiny star in a vast universe.
Though humans have named a few constellations of stars, from Orion to the Big Dipper, in reality, there are many more stars in the universe than could ever be given names.
Just how many is not exactly clear, but it's a lot. A whole lot.
One way to get at this number is to figure out the average number of stars in a typical galaxy and multiply that by the estimated number of galaxies in the universe.
Deep-field images from the Hubble Space Telescope suggest there are 10 times more galaxies in the universe than scientists previously thought, with about 2 trillion galaxies in total, according to a study published in October 2016 in the journal Science by Christopher Conselice, a professor of astrophysics at the University of Nottingham in the U.K., and his colleagues. [Video: Our Universe Has Trillions of Galaxies]
About 100 million (or 10 to the eighth power) stars inhabit the average galaxy, according to one of the best estimates, Conselice wrote in an email to Live Science.
But getting to that number was not just a matter of aiming a telescope at the sky and counting up all the twinkly bits. Only the most luminous stars in a galaxy shine brightly enough to be detected by a telescope.
In 2008, for instance, the Sloan Digital Sky Survey (which maps all observable celestial objectsin one third of the sky), detected about 48 million stars, or just half of the number estimated to exist, according to a 2008 study in the Astrophysical Journal.
A star as bright as our own sun in the neighboring Andromeda galaxy would not even be detected by traditional telescopes such as those used by the Sloan Digital Sky Survey, Space.com reported.
How Many Stars Are There in the Sky?
The Milky Way and its assorted stars, from the mountains of San Diego County (Shutterstock/Kevin Key)
You look up into the night sky. Before you—above you, around you—stretches a pitch-black canvas washed with streaks and studs of brightness. You are, you realize, surrounded by light that has traveled the expanse of the universe to reach your eyes. You feel tiny and enormous at the same time. You are, literally, awed.
But what, actually, is so awesome? How many stars are you actually seeing? Why simply marvel at the majesty and mystery of it all when you can also do some math?
Let's start with the galaxies. There are, astronomers estimate, around 170 billion galaxies in the observable universe, stretching out over a radius of some 45.7 billion* light-years.
Those galaxies vary in terms of the number of stars they contain, Universe Today notes: Some spiral galaxies have more than a trillion stars. Some giant elliptical galaxies have 100 trillion stars.
There are also tiny dwarf galaxies—tiny being, obviously, a relative term here—that have a significantly fewer number of stars.
The Milky Way—our little corner of the observable universe—has, for its part, some 400 billion stars.
So! If we multiply the (estimated) average number of stars in each galaxy by the number of galaxies in the observable universe—and carry the billion, etc.—we get a rough estimate of ALL THE STARS we're capable of observing.
And what we find is described, extremely efficiently, in the video below: There are roughly a septillion stars in the observable universe. That's 1,000,000,000,000,000,000,000,000 stars. Which is, for lack of a more fitting description …
a lot of stars.
How Many Stars are There in the Universe?
The Milky Way's core, from our gallerywcreech
When asking the question “How many stars are there in the universe?” it's important to distinguish between the universe as a whole and the observable universe. Because the universe was born 13.8 billion years ago, we can only observe objects up to a certain distance from Earth — light from more distant objects hasn’t had time to reach us yet. And to answer “how many stars are there,” we must limit the discussion to what we can observe.
Astronomers had estimated that the observable universe has more than 100 billion galaxies. Our own Milky Way is home to around 300 billion stars, but it’s not representative of galaxies in general.
The Milky Way is a titan compared to abundant but faint dwarf galaxies, and it in turn is dwarfed by rare giant elliptical galaxies, which can be 20 times more massive.
By measuring the number and luminosity of observable galaxies, astronomers put current estimates of the total stellar population at roughly 70 billion trillion (7 x 1022).
However, those estimates are dependent on the sensitivity of current telescopes. More recent estimates have upped the number of galaxies in the observable universe to 2 trillion, though many of these are tiny, fluffy galaxies with fewer stars.
If the typical galaxy had 100 billion stars, then there would be 2 x 1023 stars in the observable universe, three times as much as earlier estimates.
But even this is still probably an underestimate, as more sensitive telescopes will continue to reveal fainter galaxies and stars.
How many stars are there in my night sky?
The number of stars you see in the night sky depends on several variables, including your location’s light pollution and your own vision. In large, light-polluted cities, only a few dozen of the brightest stars may be visible – though that doesn't mean there's nothing to observe from a city. But in a clear, dark sky, a couple thousand stars become visible to the unaided eye.
If you tabulate all stars visible down to magnitude 6.5, thought to be the faintest stars still visible to the unaided eye, the entire sky contains some 9,000 stars. Since you can only see half the sky at any time, that means there are as many as 4,500 stars visible in your sky tonight.
Read more on where this number comes from in Bob King's article, “9,096 Stars in the Sky — Is That All?”
Make the most of the stars in your sky whether you live in dark-sky nirvana or under urban glow. Subscribe to Sky & Telescope for observing advice for any location in the Northern Hemisphere.
Everything you wanted to know about stars
Gently singing Twinkle, twinkle, little star may lull a baby to sleep, but beyond the confines of Earth’s atmosphere, the words aren’t exactly accurate. A correct, albeit less soothing, rendition might be: Emit, emit, gigantic ball of gas.
Stars are huge celestial bodies made mostly of hydrogen and helium that produce light and heat from the churning nuclear forges inside their cores.
Aside from our sun, the dots of light we see in the sky are all light-years from Earth. They are the building blocks of galaxies, of which there are billions in the universe.
It’s impossible to know how many stars exist, but astronomers estimate that in our Milky Way galaxy alone, there are about 300 billion.
The life cycle of a star spans billions of years. As a general rule, the more massive the star, the shorter its life span.
Birth takes place inside hydrogen-based dust clouds called nebulae. Over the course of thousands of years, gravity causes pockets of dense matter inside the nebula to collapse under their own weight.
One of these contracting masses of gas, known as a protostar, represents a star’s nascent phase. Because the dust in the nebulae obscures them, protostars can be difficult for astronomers to detect.
As a protostar gets smaller, it spins faster because of the conservation of angular momentum—the same principle that causes a spinning ice skater to accelerate when she pulls in her arms. Increasing pressure creates rising temperatures, and during this time, a star enters what is known as the relatively brief T Tauri phase.
Millions of years later, when the core temperature climbs to about 27 million degrees Fahrenheit (15 million degrees Celsius), nuclear fusion begins, igniting the core and setting off the next—and longest—stage of a star’s life, known as its main sequence.
Most of the stars in our galaxy, including the sun, are categorized as main sequence stars. They exist in a stable state of nuclear fusion, converting hydrogen to helium and radiating x-rays. This process emits an enormous amount of energy, keeping the star hot and shining brightly.
Some stars shine more brightly than others. Their brightness is a factor of how much energy they put out–known as luminosity–and how far away from Earth they are. Color can also vary from star to star because their temperatures are not all the same. Hot stars appear white or blue, whereas cooler stars appear to have orange or red hues.
By plotting these and other variables on a graph called the Hertzsprung-Russell diagram, astronomers can classify stars into groups. Along with main sequence and white dwarf stars, other groups include dwarfs, giants, and supergiants. Supergiants may have radii a thousand times larger than that of our own sun.
Stars spend 90 percent of their lives in their main sequence phase. Now around 4.6 billion years old, Earth’s sun is considered an average-size yellow dwarf star, and astronomers predict it will remain in its main sequence stage for several billion more years.
As stars move toward the ends of their lives, much of their hydrogen has been converted to helium. Helium sinks to the star's core and raises the star's temperature—causing its outer shell of hot gases to expand. These large, swelling stars are known as red giants. But there are different ways a star’s life can end, and its fate depends on how massive the star is.
The red giant phase is actually a prelude to a star shedding its outer layers and becoming a small, dense body called a white dwarf. White dwarfs cool for billions of years.
Some, if they exist as part of a binary star system, may gather excess matter from their companion stars until their surfaces explode, triggering a bright nova. Eventually all white dwarfs go dark and cease producing energy.
At this point, which scientists have yet to observe, they become known as black dwarfs.
Massive stars eschew this evolutionary path and instead go out with a bang—detonating as supernovae.
While they may appear to be swelling red giants on the outside, their cores are actually contracting, eventually becoming so dense that they collapse, causing the star to explode.
These catastrophic bursts leave behind a small core that may become a neutron star or even, if the remnant is massive enough, a black hole.
Because certain supernovae have a predictable pattern of destruction and resulting luminosity, astronomers are able to use them as “standard candles,” or astronomical measuring tools, to help them measure distances in the universe and calculate its rate of expansion.
Depending on cloud cover and where you’re standing, you may see countless stars blanketing the sky above you, or none at all. In cities and other densely populated areas, light pollution makes it nearly impossible to stargaze. By contrast, some parts of the world are so dark that looking up reveals the night sky in all its rich celestial glory.
Where Are the Stars? See How Light Pollution Affects Night Skies
Of the many ways Earth is polluted, light pollution may be the least talked about. This short film, shot mainly in California by Sriram Murali, goes through all the levels of the scale, showing how the view of the cosmos gets better in less light-polluted areas.
Ancient cultures looked to the sky for all sorts of reasons.
By identifying different configurations of stars—known as constellations—and tracking their movements, they could follow the seasons for farming as well as chart courses across the seas. There are dozens of constellations.
Many are named for mythical figures, such as Cassiopeia and Orion the Hunter. Others are named for the animals they resemble, such as Ursa Minor (Little Bear) and Canus Major (Big Dog).
Today astronomers use constellations as guideposts for naming newly discovered stars. Constellations also continue to serve as navigational tools.
In the Southern Hemisphere, for example, the famous Southern Cross constellation is used as a point of orientation. Meanwhile people in the north may rely on Polaris, or the North Star, for direction.
Polaris is part of the well-known constellation Ursa Minor, which includes the famous star pattern known as the Little Dipper.
Ask Ethan: How Many Stars In The Night Sky Still Exist?
An animation sequence of the 17th century supernova in the constellation of Cassiopeia. Image… [+] credit: NASA, ESA, and the Hubble Heritage STScI/AURA)-ESA/Hubble Collaboration. Acknowledgement: Robert A. Fesen (Dartmouth College, USA) and James Long (ESA/Hubble).
When we look out at the Universe, we take for granted that what we see is what's actually there at that particular moment in time. Yet this isn't quite the case. There were delays with the Apollo astronauts because light signals took a little over two seconds apiece to make a round trip.
The Mars rovers need to robotically pilot themselves, because the multi-minute delays are too great for a human to have to manually change their headings. And if you go beyond the Solar System, the distances to the stars are measured in light years, which means we're looking back in time whenever we see a distant object.
How do we know that what's there matches what we see? Matt Lanka wants to know:
[H]ow many of the stars observable from Earth still exist? Since the light from many of them has traveled hundreds, thousands, even millions of light years to get here, is it not possible that many of the stars we see in fact burned out or exploded centuries or [millennia] ago and the light (or lack thereof) simply hasn’t reached us yet?
The answer depends very much on how far you're willing to look.
The night sky as seen from the California Coastal National Monument, similar to what human eyes… [+] could ideally see. Image credit: Bureau of Land Management, under a cc-by-2.0 license.
With the naked eye under ideal conditions — complete darkness, no light pollution, no clouds, no Moon, full-sky (both hemispheres) viewing, etc. — there are a total of just over 9,000 stars that the human eye can discern.
Every single one of them is contained within our own galaxy, though, so none of these are millions of light years away. There are some that are thousands of light years distant, though.
Deneb, one of the sky's brightest stars (and a vertex of the summer triangle) is approximately 2,600 light years away, while the most distant naked-eye star is V762 Cas at just over 16,000 light years.
The summer triangle, with Deneb visible as the bright star along the left of the image. Image… [+] credit: Eric Teske under a cc-by-2.0 license, via http://www.ericteske.com/2012/05/my-first-point-and-shoot-milky-way.html.
But the vast majority of stars we can see are only a few hundred light years distant, or even less. While we think of stellar deaths as an all-of-a-sudden mechanism, in reality the life cycle of stars means that there are a number of important phases a star goes through on its way towards death. In particular, they:
- need to expand into a red giant and begin burning helium,
- need to burn through the helium in their core and begin fusing carbon,
- burn through their core's carbon and begin fusing oxygen and heavier elements, up until silicon produces iron, nickel and cobalt,
How Many Stars Are In the Universe?
Today’s Wonder of the Day was inspired by Kayla. Kayla Wonders, “How many stars are there?” Thanks for WONDERing with us, Kayla!
Have you ever stared up at the stars in the night sky and wondered how many there are? If so, you're not alone. That question has fascinated astronomers, artists, and dreamers of all ages since the beginning of human history.
Famous astronomer Carl Sagan once estimated that there must be “billions upon billions” of stars in the universe. If you've ever tried to count the stars in the night sky, you may have concluded that it would be impossible to count them all.
Guess what? You'd be absolutely right!
Before we get to the mind-boggling estimates that modern astronomers have made, let's start “small” and get some perspective. We live on planet Earth, which orbits around a star we call the Sun.
The Earth and the Sun, along with several other planets, make up a solar system, which is part of a larger grouping of stars called a “galaxy.”
Our particular galaxy is known as the Milky Way. Scientists estimate that there are 200 billion to 400 billion — yes, that's billion with a “b” — stars in the Milky Way galaxy. The Sun is just one of those 200 billion to 400 billion stars.
If that blows your mind, just wait! Our Milky Way galaxy is just one of the many galaxies in our universe.
How many? Believe it or not, astronomers estimate there are 100 billion to 200 billion galaxies in the universe, each of which has hundreds of billions of stars.
If your mind is reeling, that's OK. It's hard for most people to imagine the size of the universe. So how many stars are there? In truth, there are too many to count. Current estimates are just guesses.
Even using our most advanced telescopes and technology, we still cannot see to the ends of our universe. Further complicating things, closer stars that are particularly bright also block our ability to see beyond them in certain directions.
Scientists use observations and data we do have, along with assumptions about our galaxy and the other galaxies in the universe, to estimate the number of stars. Recently, though, some scientists challenged some of the assumptions scientists have been using for years.
The result? Scientists now believe there may be three times more stars than scientists previously estimated.
Why? Astronomers now believe there may be many more red dwarf stars — the most common type of star in the universe — than previously thought.