Light Years

[Abid]

How the distances between two galaxys, stars etc are measured using "light year" unit????????

[tanvirab]

A light year = distance traveled by light in one year

[Abid]

I know that. But how it is measured. I mean with what?

[tanvirab]

It's measured the same way as any other distance. It's just a unit, not a new quantity. Your choice of unit does not change your measurement.

[Mohaimin]

It's measured the same way as any other distance. It's just a unit, not a new quantity. Your choice of unit does not change your measurement.

I think he is asking "what is the mechanism of the measurement?".

[tanvirab]

That's what I said. The mechanism of measurement does not depend on the unit. For example, How do you measure the length of a cricket pitch? You take a ruler and put it on the pitch see the scale on the ruler. Now you can have the ruler in meters, inches, light years or your favorite unit of length. The measurement is the same.

[tanvirab]

Are you asking about how we measure the distance light travels in one year?

[Abid]

I want to know with "what" it is measured and how. Suppose the distance between "X" and "Y" is 1000 light years. You can't measure this by scale. So how can you measure this?

[tanvirab]

Ok. So your question is how do we measure very large distances where we cannot go because they are so far away. It does not have anything to do with light years. You measure the distance in any units in the same way.

To measure very large distances, there are many indirect methods. The answer will depend on how much physics you know. Do you know some trigonometry? Luminosity, Intensity of radiation, flux etc.? Doppler effect?

[Abid]

yep except about intensity of radiation and spherical trigonometry