A striking couple (1)
Here are images of the Eagle Nebula taken in the light given off by its
hydrogen atoms (1) and its sulfur ions (2). Click between the two pictures to compare how
the nebula looks in the two images.
If you're curious as to where these atoms' so-called emission lines fall on the
visible-light spectrum, see the graph below. The
wavelengths of the light picked up by the WFPC2's hydrogen and sulfur filters
are 6563 and 6725 angstroms, respectively. (One angstrom is equal to one
ten-billionth of a meter.) The corresponding wavelength for light coming
through the oxygen filter is 5007 angstroms.
We now have three images, each showing us light from a different type of atom.
Now, the best way to see the differences among these three images is to make
each of the three a different color, then use our color vision to tell us how
the nebula's properties are changing from place to place.