Question:
I have seen pictures of the beautiful M16 Eagle Nebula.
Can you please provide an easy to understand description of
what I am seeing in the picture, including why the photo is
so colorful (is that really what it looks like?).

Answer from Sanjay Limay on April 3, 1996:
I assume you are referring to the HST image of the Eagle Nebula
(STScI-PRC95-44a).  Most other images of the nebula look red or reddish.
The HST image is a composite of three images taken through three different
filters- the red filter shows emission from sulfur atoms from which one
electron has been stripped off, the green shows emission from hydrogen
atoms, and the blue filter shows light emitted by oxygen atoms from which
two electrons have been stripped off.  Thus, the color composite shows the
differing emissions, and hence presence of these three atomic species in the
nebula.  To a large extent, the "color" tends to indicate the abundance of
that particular species.  There probably are other species in the nebula,
and their presence (emission of light) can also influence the color.

Since I don't know which specific image you are referring to, I will defer a
longer explanation of what you are seeing in the pictures.  If it is the HST
image, then you may want to study the caption accompanying that picture,
which is available over the web at the STScI site.