How do scientist measure the vast distances across our cosmos?

Question

Since light travel at 186,500 a second how is it possible to accurately measure a star a million light years away how do they verify that this measurement is correct what method do they use I hope I can find a real scientist to explain or at least someone knowledgable in astronomy.

Answer 1

This is very hard! The larger the distance the less accurate our guesses become. We use standard candles and what we call the distance ladder. Standard candles are stars that have luminosities that we know. We measure their apparent magnitude and compare to their absolute magnitude and by this we can derive a pretty good guess of distance up to a point (hoping of course that there is no variation we don't know about) and then we have to use the next rung of the distance ladder.


http://en.wikipedia.org/wiki/Standard_candles
http://en.wikipedia.org/wiki/Cosmic_distance_ladder

Answer 2

They really cannot measure such large distances accurately.

Stars as far away as 100 light years or so can be measured by the parallax method. Parallax is triangulation, where we measure the angle from Earth to the star twice, with the 2nd measurement being made 6 months later than the first so that it is taken from the opposite side on the Sun in Earth's orbit. From those two angles and the known size of Earth's orbit they draw a big triangle and can calculate all the sides and angles of that triangle with trigonometry. We cannot do this for all stars because the distance is millions of times more than the size of Earth's orbit and the angles get too small to measure. The triangle gets too long and skinny to measure accurately.

Measurement of any star more distant than that depends on figuring out how bright the star really is and then comparing that to how bright it appears in the sky. The farther away it is the dimmer it looks. But the farther away the star is, the more indirect and unreliable the measurement is.

Answer 3

There are some good answers here.
They use luminosity to verify triangulation and vica versa.
Edwin Hubble discovered that farther stars were travelling away from us so he could use the Doppler shift as a gauge; up to the red-shift limit.

Answer 4

light year