Night skies photographer Amit Ashok Kamble recorded this exceptional panorama that the Milky means over Pakiri Beach, brand-new Zealand by stitching 10 images together into a finish mosaic. Image submitted may 5, 2014.(Image credit: Amit Ashok Kamble)
The Milky means is the galaxy in i beg your pardon the earth resides. Part of it is visible on a clean night from Earth, as a thick tape of stars stretching across the sky. We have the right to see countless these stars with the nude eye, and also many more in a telescope. But how countless stars in the Milky Way?

"It"s a surprisingly challenging question come answer. Girlfriend can"t just sit around and count stars, generally, in a galaxy," claimed David Kornreich, an assistant professor in ~ Ithaca university in brand-new York. He was the founder of the "Ask one Astronomer" service at Cornell University.

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Even in the Andromeda Galaxy — i m sorry is bright, big and reasonably close through Earth, at 2.3 million light-years far — only the largest stars and a few variable stars (notably Cepheid variables) are bright sufficient to shine in telescopes from that distance. A sun-size star would certainly be too difficult for united state to see. So astronomers estimate, using some of the methods below.

The Milky Way"s structure

From observations, astronomers know that the Milky way is a ban spiral galaxy the is around 100,000 light-years across. A view outside the galaxy would expose a central bulge surrounded by four arms, two significant and 2 minor. The Milky Way"s major arms are well-known as Perseus and Sagittarius. The sun is situated in one of two young spurs, which is called the Orion Arm.

The galaxy additionally has a substantial hot-gas halo approximately it the is several hundreds of thousands the light-years in diameter. Astronomers estimate that the gloriole is simply as substantial as all of the stars in the Milky Way. Numerous of the Milky Way"s stars, however, are difficult to view. The is since the center of the galaxy has a galactic bulge filled through stars, gas and also dust — and also a supermassive black hole. This area is so thick with material that even powerful telescopes can not see with it. Astronomers aren"t sure when and how the bulge formed; some imply that the Milky Way"s early history was readjusted when the galaxy collided with one more one.

Astronomers provided to think that all of the stars in the universe were situated inside of the Milky Way, but that readjusted in the 1920s. Astronomer Edwin Hubble supplied a star referred to as a Cepheid variable to measure ranges in the sky. From there, astronomers learned the there were totality galaxies in the universe separate from the Milky Way.

Massive investigation

The primary method astronomers estimate stars in a galaxy is by identify the galaxy"s mass. The massive is estimated by spring at how the galaxy rotates, as well as its spectrum making use of spectroscopy.

All galaxies are relocating away from each other, and also their light is change to the red end of the spectrum due to the fact that this stretches the end the light"s wavelengths. This is called "redshift." In a rotating galaxy, however, there will certainly be a part that is more "blueshifted" because that part is slightly relocating toward Earth. Astronomers must also know what the inclination or orientation that the galaxy is prior to making an estimate, i m sorry is sometimes merely an "educated guess," Kornreich said.

A technique called "long-slit spectroscopy" is finest for performing this type of work. Here, an elongated thing such as a galaxy is regarded through an elongated slit, and the light is refracted utilizing a an equipment such as a prism. This division out the color of the stars into the colors of the rainbow.

Some the those colors will certainly be missing, displaying the exact same "patterns" of missing portions as specific elements of the regular table. This lets astronomers number out what elements are in the stars. Each type of star has a unique chemical fingerprint the would show up in telescopes. (This is the basis of the OBAFGKM sequence astronomers use to distinguish between species of stars.)

Any sort of telescope can do this kind of spectroscopy work. Kornreich often uses the 200-inch telescope in ~ the Palomar Observatory in ~ the California institute of Technology, however he included that nearly any telescope of enough size would be adequate.

The ideal would be making use of a telescope in orbit since scattering occurs in Earth"s setting from light pollution and additionally from natural events — even something as simple as a sunset. The Hubble an are Telescope is one observatory recognized for this kind of work, Kornreich added. A follower observatory called the James Webb an are Telescope is expected to beginning in 2020. The challenge, however, is the Hubble is a telescope in high need – and also the very same is meant of Webb after its launch. So the observatories can"t spend every one of their time estimating galaxy mass.

How much of the massive is stars?

Between different galaxies the the same mass, there could be variances as to the species of stars and also the overall mass. Kornreich cautioned this would be really hard come speak about generally, but said the one difference might be looking at elliptical galaxies vs. Spiral galaxies such together our own, the Milky Way. Elliptical galaxies tend to have an ext K- and also M-type red dwarf stars than spiral galaxies. Due to the fact that elliptical galaxies room older, lock will have less gas because that was blown away during their evolution.

Once a galaxy"s massive is determined, the various other tricky point is figuring out exactly how much of that mass is made of stars. Many of the mass will be consisted of of dark matter, a kind of matter that emits no light yet which is thought to consist of most that the fixed of the universe.

"You have to model the galaxy and also see if you can understand what the percent of that mass the stars is," Kornreich said. "In a common galaxy, if you measure up its fixed by looking in ~ the rotation curve, around 90 percent of that is dark matter."

With much of the staying "stuff" in the galaxy consisted of of diffusive gas and dust, Kornreich approximated that about 3 percent of the galaxy"s mass will be comprised of stars, yet that might vary. Further, the size of the stars chin can substantially vary indigenous something the is the size of ours sun, come something dozens that times smaller sized or bigger.The number of stars is roughly …

So is over there any method to number out how many stars for sure? In the end, that comes down to an estimate. In one calculation, the Milky means has a mass of about 100 billion solar masses, so the is simplest to interpret that to 100 exchange rate stars. This accounts because that the stars that would be bigger or smaller sized than ours sun, and also averages castle out. However, the massive is difficult to calculation — other approximates have stated the galaxy has actually a massive of between 400 billion and 700 billion solar masses.

The European an are Agency"s Gaia mission is mapping the locations of approximately 1 billion stars in the Milky Way. ESA states Gaia will map 1 percent the the stellar contents in the Milky Way, which place the estimate of the complete stars in our galaxy at 100 billion. Gaia"s score is to do the best-ever three-dimensional map that the Milky Way.

The caveat, Kornreich said, is that these numbers room approximations. More advanced models deserve to make the approximation more accurate, yet it would be very complicated to count the stars one by one and tell you for certain how many are in the galaxy.

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If you desire to try and record the Milky method yourself, we have actually guides come the finest cameras for astrophotography and the finest lenses because that astrophotography, to help you see as lot of the mechanism as possible.

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Elizabeth Howell is a contributing writer because that who is among the few Canadian journalists to report frequently on an are exploration. She is the writer or co-author the several books on an are exploration. Elizabeth stop a Ph.D. From the university of phibìc Dakota in Studies, and an M.Sc. Indigenous the very same department. She also holds a bachelor that journalism degree from Carleton university in Canada, wherein she began her career in 2004. As well as writing, Elizabeth teaches communications at the university and also community college level, and for government training schools. To check out her recent projects, follow Elizabeth top top Twitter at