Can any one explain what the purples and signs are in this picture?
Well judging from what I can see (I don't know what that is actually showing), I see the constellations in white, the purple may be stars either not relevant to the diagram or (based on the condensed strip shape) it might have something to do with the Milky Way.
The only thing for certain that I know about this is that the white dots are definitely the constellations. Sorry I couldn't be much help on this one.
From http://www.einsteinathome.org/about/screensaver.html [Broken]:
"Pulsars and Supernovae Remnants
Pulsars and Supernovae are shown on the sky because scientists believe they emit gravitational waves. The purple dots on the celestial sphere mark the locations of pulsars* that have already been detected. These are clustered in the plane of our galaxy, the Milky Way, and are mostly near the center of the galaxy. They are likely sources of gravitational waves."
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