Flying Colors

To the naked eye, Comet Lulin may have a vaguely pale green look when it passes about 38 million miles from Earth on Tuesday.  We’re told it’s already been visible where the sky is clear and city lights don’t interfere, high in the northern sky after midnight in the U.S. To the eye of a NASA probe called Swift, it looks very different.  Here’s their image:
Click on the picture to enlarge; it’s one of those that is best enjoyed big.  The colors are not just for our pleasure; the blue and green come from the probe’s UltraViolet and Optical Telescope (UVOT for short), while the red is what Swift observes in the X-ray range.  The stars were added from earthly observations; that’s the constellation Libra in the background. "In the Swift images," says NASA, "the comet’s tail extends off to the right. Solar radiation pushes icy grains away from the comet. As the grains gradually evaporate, they create a thin hydroxyl tail. Further from the comet, even the hydroxyl molecule succumbs to solar ultraviolet radiation. It breaks into its constituent oxygen and hydrogen atoms." NASA quotes Dennis Bodewits, a member of the Swift team at the Goddard Space Flight Center in Greenbelt, Md: "The UVOT data show that Lulin was shedding nearly 800 gallons of water each second."  That’s enough, they say, to fill an Olympic-size swimming pool every 15 minutes. NASA’s Jet Propulsion Lab has an interactive diagram that allows you to follow the comet’s path from different angles; take a look HERE.  Sky & Telescope is providing a regularly-updated page of comet observations, with pictures and information on where to find the comet; click HERE. Most of us will miss the show.  That’s the price we pay for city lights and urban haze.  In the meantime, enjoy the pictures. Image Credit: NASA/Swift/Univ. of Leicester/DSS (STScI, AURUA)/Bodewits et al.