if a star is 10million light years away how do we know it is that far, as in how do we measure the distance?

Answer 1

At that distance you are talking about a star in another galaxy in our Local Group. The Andromeda Galaxy for example is 2.5 million light years away. The distance to the Andromeda Galaxy was examined by Edwin Hubble using the Hooker 100 inch telescope in the 1920s. The distance was established using observations of Cepheid variable stars. These stars are believed to have a certain brightness for a given period of variability. This relationship came from examining such stars in our own galaxy where we could use various methods of distance determination or in star clusters where we can make the assumption that all the stars are approximately the same distance from us. So you observe the period of the Cepheid variable, that tells us its brightness and its observed brightness enables us to work out how far away it is.

Distance determination using galaxy red-shift applies at larger length scales. At 10 million light years a galaxy may well be moving toward us (as is Andromeda) and so we cannot use red-shift to estimate a distance.

Answer 2

They don't use parallax for objects at that distance. As others have said, they use the brightness of a type of star called a Cepheid variable to determine the distance. For objects in the many millions to billions of light years, they use the amount of red shift in the objects' light spectrums.

Sorry, I mean spectra : )

Answer 3

That would be a star in another Galaxy.
That galaxy is moving away from us and therefore the light is red shifted.
That is due to the doppler effecte wavelengths are elongated with movement.
The furher away galaxies are the faster they are moving hence the greater the red shift.

Answer 4

properly, it is already occurring. in the time of a stars lifetime, it of direction emits radiation interior the form of sunshine. the gentle from a "lifeless" action picture star replaced into emitted from the action picture star on an analogous time as the action picture star replaced into nonetheless lively. so as that even although a action picture star has long previous supernova, the gentle it emitted keeps its journey by using area, unaffected via the death of its unique source. working example, here in the international radio alerts are spewing into area consistently. Even the 1st radio transmissions, from many years previous, are suitable now traveling by using area. If we've been to be destroyed day after today, the radio alerts we emitted previously our death will proceed traveling by using area, comparable ingredient is going for gentle. as long through fact the gentle comes from a action picture star that isn't previous the form horizon, it is going to at last attain us if we wait long adequate.

Answer 5

light years are measured in the time it takes for light to travel in a year.

Answer 6

good question no easy answer this link shows you 26 ways distance in space is measured

http://www.astro.ucla.edu/~wright/distance.htm

Answer 7

astronomers use a method called triangulation or parallax

this page will help you
http://science.howstuffworks.com/question224.htm

Answer 8

perhaps they get out their little tape measures

Answer 9

they use parallax calculations