|When we look in different
directions of the sky,
we often see dark "holes" in the distributions of stars.
These are not
gaps where there are no stars, but instead are interstellar
Dust doesn't have to come just in thick clouds, it can also be spread diffusely throughout space.
What does dust do to star light? Several things:
|So we have
If we define extinction
as A=1.086, we
can then correct the observed magnitudes: m = mobs -
A. (Why is it minus A?)
So if we measure the B-V color of a star, we will be measuring a redder color than the true B-V color (usually called (B-V)0). We define the reddening as
Now it seems reasonable to expect that the more extinction there is, the more reddening there will be. In fact, studies have shown that the extinction and reddening are related by:
E(B-V) = (B-V) - (B-V)0
|The extinction is not due to
Dust absorbs and scatters light.
|So we see not only dark clouds, but reflection nebulae as well...|