How can we tell how far away a star is?

Answer 1

We use parallax. As we travel around the sun we measure the angle to the star at the two extremes and use trig to find the distance.

Answer 2

The distances to stars are measured in three interrelated ways.

First, the nearest stars, say less than 1000 light years (ly), can have their distances measure through "parallax." If you hold your hand in front of you, one hand much closer than the other, and then open and close one eye at a time, you will see the near hand move more than the far hand. The different location of each eye gives a different perspective of each hand.

The same of true of the stars. As the earth moves from one side of its orbit to the opposite side near stars will appear to move more than far stars --most stars are so far away they appear "fixed". With a little geometry and algebra the actual distance to the star can be calculated.

Second, a star can be bright because it is nearby, or because while it is very far away it is intrinsically bright. For example, a 40 watt light bulb is dimmer than a 100 watt light bulb, but if it is nearer it will look as bright or brighter than a 100 watt bulb. Take a search light far enough away and it will look like a 40 watt bulb, even though it is many, many times brighter that a 40 watt bulb. So, lots of research is spent trying to figure out how bright a star actually is, so its distance can be computed from its apparent brightness. For example, if we see a star the same color and mass of the sun complete with the same spectrum of the sun and the same age as the sun, we can conclude that they are roughly the same brightness. That means we can tell how far away the star is based on its apparent brightness (there is a nice formula for doing this).

Third, a star may "behave" in a way that gives information about its actual brightness. The so-called "Cepheid variables" are like this. They get brighter and dimmer over the course of a few days, and the length of this cycle is directly related to how bright they are. Fortunately, the closest ones have their distances measured by parallax. There are several types of stars that have behavious more or less connected to their brightness.

Finally, there are the super novae. These stars can be as bright, or brighter, than an entire galaxy! It is assumed that at their brightest they are all roughly the same brightness. This turns out not to be exactly true (there are at least 2 different kinds of super novae) but it is roughly true.

HTH

Charles

Answer 3

Stars over 400 light years away can't be properly measured with parallax, so we just try to make guesses at there distance based on what we know about the stars that are closest to us. Using this information and trying to use it to extrapolate information from unknown systems (distant galaxies) obviously leaves enormous room for error. Scientists usually come up with a preconceived hypothesis that sounds good to them, and then create models and tests that will end of complying with what they have already decided was going to be the answer that they were looking for. This strategy works very well, always!

Answer 4

We can triangulate on nearby stars by observing the angle to them now and the n 6 months from now. That gives us a triangle with one side equal to the diameter of Earth's orbit and all the angles known. For more distant stars we have to figure out how bright they really are based on stellar evolution models or whatever and compare that to how bright they appear to us in order to calculate the distance.

Answer 5

there is a special type of star call a Cepheid Variable because the first one was in the contellation Cepheus.
It gets brighter and darker every few days. We know that its brightness is related to the amount of time between the peaks of its brighness.

Since we can know its absolute brightness than based on its apparent brightness we can tells it distance.

So by studying these variable stars in clusters and galaxies we can tell their distance.

Answer 6

well since space is well over a billion miles away and for the fact that all stars are is large bodys of mass its actually quite hard to determine the actual distance from earth to a star but if you want to know go to this web site

Answer 7

Atomic elements absorb light at certain frequencies. and this leaves dark lines in a star's spectrum. The farther from us the star is, the more these lines shift towards the red end (low freq) of the spectrum.

Answer 8

get a telescope.