How It Sees

Spanking clean
This is the final, fully cleaned-up version of the PC1 image—or at least one of the PC1 images. Remember that a picture was taken with the PC1 through each of four filters. Each filter records light emanating from the target object—in our case the Eagle Nebula—in very specific parts of the visible-light spectrum.

Different types of atoms, it turns out, emit light at very specific wavelengths—that is, very specific colors. This allows astronomers like me to take images that only show the light coming from specific types of atom. For the Eagle Nebula image, the WFPC2 used filters that took images in the light of three kinds of atoms: hydrogen atoms, sulfur atoms with one electron removed (sulfur ions), and oxygen atoms with two electrons removed (doubly ionized oxygen). A fourth filter sees only starlight, which lights up the dust that is mixed in with the nebula's gas.

The PC1 image that we've been manipulating was taken with the oxygen filter. The first step in getting the PC1 image together with its Wide Field mates is to obtain cleaned-up versions of the three WF images also taken with the oxygen filter.

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