When you are star gazing, and you see a star that is brighter than another..?

Question

is this because it is closer to Earth than the other, or is it because one is hotter than the other.

And how far is the average star from Earth?

Answer 1

How bright a star is as seen from Earth can be attributed to it's proximity, or because it's a very bright star. Two stars that appear similar might, in fact, be a small star that's very close, and a very large star that's very far away.

The "average" distance of stars is hard to fathom, but most the stars we see without a telescope are within a 100 or 125 light years.

Answer 2

Stars can appear brighter because they are closer.
Stars can appear brighter because they are... brighter (more luminous).

Stars that we see with our eyes are all within our own arm of the Milky Way. Stars in the spiral arms that are neighbours of our spiral arm are, in general, too far to be seen as individual stars; however, our eyes (and brain) interpret their total light as a sort of milkyness in the sky (hence the name of the Galaxy).

The closest stars (other than the Sun) form a triplet, a little over 4 light-years away. Two reasonnably bright stars and a tiny one. Presently the tiny one is the closest to us of the three (it is called Proxima Centauri: Proxima because it is the closest, in our proximity; Centauri because it is in the constellation of the Centaur.

The two other ones are so close together that they are seen as one, called Rigil Kentaurus. It appears as bright as Vega.

If we could place ourselves so that we'd be at equal distance from the Sun and Rigil Kentaurus, R.G. would appear a bit brighter than our Sun (not by much). Of course, our Sun being much closer, appears a lot brighter from Earth.

I have in front of me a list of the 314 brightest stars (apparent brightness, as seen from Earth). Most distances are in hundreds of light-years, although I see a dozen or so beyond 3,000 light years.

There is a column giving me "Absolute" brightness. This is how bright the star would like if it were placed at a standard distance from Earth (10 parsec = 32.6 light years).

The Sun would be barely visible.

The furthest star in that list goes by the very poetic name of: iota-one Scorpii (it has no proper name).
Its distance is indicated as 4000 light years (with a question mark). Its true luminosity is 131,000 times more than our Sun.

Now that is brilliant.

Despite that, at 4000 light years, it appears as a 3rd magnitude star (about the same as the star that marks the link between the bowl and the handle of the Big Dipper -- delta Ursae Majoris, a.k.a. Megrez)


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The true luminosity of a star depends on its mass (and its temperature, but for most stars, the temperature depends on the mass) and its surface area.

A hot star that is small will be less luminous than a hot star that is large.

A cool star that is very large may still be more luminous than a hot star that is not as large. See Betelgeuse for example.
http://en.wikipedia.org/wiki/Betelgeuse

In general, the bigger the star, the hotter it must be to prevent the collapse of its core under its own mass.

Answer 3

it's not because it's hotter. temperature in stars effects color, not brightness.
it's because it's bigger, or it's closer, and there's no way to tell which unless you do some measurements using astronomical equipment.

there's really no such thing as an average star distance. the closest star (except the sun) is proxima centauri, about 4 light years away. (a light year is the distance light travels in a year. it is distance, not time.) stars can be as many as 2 billion light years away, or more.

Answer 4

It can be for either reason. Nearer stars of equal absolute brightness will appear brighter, and larger stars at the same distance will also appear brighter. Most of the stars we see with our naked eyes are relatively close to the Sun, from 4 light years to about 4 thousand light years. With telescopes, we can see stars much farther away, billions of light years away in fact.

Answer 5

Its affected by the distance, as you can see that Venus & mars are clearly more brighter than any other star on the nite sky.

Answer 6

http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html
Click this link to read about Alpha Centauri, the closest stellar system to our Sun.The brightness of a star is due to many things,like size, distance, the reflection of light..Proxima centauri is the closest star to our sun.

Answer 7

it's bigger, or it's closer