Exploring Stars in Our Galaxy - Full Documentary

Exploring The Southern Stars - Full Documentary
"Billions and billions" of stars in a galaxy (after a quote often mistakenly attributed to Carl Sagan) is how many people imagine the number of stars you would find in one. Is there any way to know the answer for sure?

"It's a surprisingly difficult question to answer. You can't just sit around and count stars, generally, in a galaxy," said David Kornreich, an assistant professor at Ithaca College in New York State. He was the founder of the "Ask An Astronomer" service at Cornell University.

Even in the Andromeda Galaxy — which is bright, large and relatively close by Earth, at 2.3 million light-years away — only the largest stars and a few variable stars (notably Cepheid variables) are bright enough to shine in telescopes from that distance. A sun-size star would be too difficult for us to see. So astronomers estimate, using some of the techniques below.

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Massive investigation
The primary way astronomers estimate stars in a galaxy is by determining the galaxy's mass. The mass is estimated by looking at how the galaxy rotates, as well as its spectrum using spectroscopy.

All galaxies are moving away from each other, and their light is shifted to the red end of the spectrum because this stretches out the light's wavelengths. This is called "redshift." In a rotating galaxy, however, there will be a portion that is more "blueshifted" because that portion is slightly moving toward Earth. Astronomers must also know what the inclination or orientation of the galaxy is before making an estimate, which is sometimes simply an "educated guess," Kornreich said.

A technique called "long-slit spectroscopy" is best for performing this type of work. Here, an elongated object such as a galaxy is viewed through an elongated slit, and the light is refracted using a device such as a prism. This breaks out the colors of the stars into the colors of the rainbow.

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

Any kind of telescope can do this sort of spectroscopy work. Kornreich often uses the 200-inch telescope at the Palomar Observatory at the California Institute of Technology, but he added that almost any telescope of sufficient size would be adequate.

The ideal would be using a telescope in orbit because scattering occurs in Earth's atmosphere from light pollution and also from natural events — even something as simple as a sunset. The Hubble Space Telescope is one observatory known for this sort of work, Kornreich added.
The number of stars is approximately …
So is there any way to figure out how many stars are for sure? In the end, it comes down to an estimate. In one calculation, the Milky Way has a mass of about 100 billion solar masses, so it is easiest to translate that to 100 billion stars. This accounts for the stars that would be bigger or smaller than our sun, and averages them out. Other mass estimates bring the number up to 400 billion.

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

[rusty]

This is not about stars or the galaxy. This is about telescopes and the astronomers themselves. If that interests you, enjoy. But if you came here to learn about stars, don't waste your time.

[justaguyreal]

I get so mesmerized at the fact of so many countless stars density in the night sky that those are only a tiny decision of the galaxies own starts, none the less the universe, and how far they are.

[justaguyreal]

Hard to imagine having more stars in universe than sand grains on all the beaches.

[caiotefu]

Thanks for the time and effort to upload... much appreciated : ) !

[xxxxxxxxxxxxxxxxxxxxx]

As a child I always wanted to know what was beyond our

[rooster]

Great documentary thanks for the post. Space is so complex and so infinitely great.

[richardcalf]

4:24 This is quite literally where I live. Amazing! It's Cape Town!!!

[minerdad]

New subbed here, great videos, .much appreciated

[themyceliumnetwork]

this is a infomercial for the ESA, very good though, would be better without all the non-space info,
great views of the universe.

[suzianderson]

Some amazing stuff, I am working volunteering for Zooniverse and some of the work is working with data from various places its really got me mad interested in Astronomy and I am trying to learn as much as I am able, even trying Obsessed, yup!!!!

[josephboateng]

I think the universe is a subset a universal set.
Thanks for the post.

[zwelonkeericbeato]

Would have loved to gain more insight about star clusters in the universe but i feel i know more about ESOR, telescopes and Europe's contribution.

[vforgamify]

Isn't it ironic that Cosmologists are obsessed with naming telescopes "large", "very large" and "extremely large"?

[morganhamilton]

Wait til you see the sun and the moon come closer together this December 21st! I can’t wait!

[saskoilersfan]

Earth is the center of another world..that's how it floats.
That's why there are stars.

[saskoilersfan]

Earth sits inside another world and the sun creates stars through the holes in the crust...

[infinitemultiversebeliever]

There are 10 Trillions Galaxies in the Observable Universe.

[ChiefCedricJohnson]

Genesis 1:16
And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.

[russellestes]

BILLIONS OF STARS, MOONS, AND PLANETS ....YET NOT ONE FLAT!!! come out of the dark age, reject the flat earth idea... WE never...never...never see a picture of a flat earth...yet every nation that has gone into space has sent back pics. of a ROUND EARTH!

[carolinecollett]

Xi (ξ) Draco, Grumium, is a yellow star in the jaw of the Dragon 🐉