Editing X-ray astronomy (section)

===Comet Lulin===
[[File:Comet Lulin Jan. 28-2009 Swift gamma.jpg|thumb|right|Image of Comet Lulin on 28 January 2009, when the comet was 99.5 million miles from Earth and 115.3 million miles from the Sun, from [[Swift Gamma-Ray Burst Mission|''Swift'']]. Data from Swift's Ultraviolet/Optical Telescope is shown in blue and green, and from its X-Ray Telescope in red.]]
{{main|Comet Lulin}}
NASA's [[Swift Gamma-Ray Burst Mission]] satellite was monitoring [[Comet Lulin]] as it closed to 63 Gm of Earth. For the first time, astronomers can see simultaneous UV and X-ray images of a comet. "The solar wind—a fast-moving stream of particles from the sun—interacts with the comet's broader cloud of atoms. This causes the solar wind to light up with X-rays, and that's what Swift's XRT sees", said Stefan Immler, of the Goddard Space Flight Center. This interaction, called charge exchange, results in X-rays from most comets when they pass within about three times Earth's distance from the Sun. Because Lulin is so active, its atomic cloud is especially dense. As a result, the X-ray-emitting region extends far sunward of the comet.<ref name=Reddy>{{cite web|author=Reddy F |title=NASA's Swift Spies Comet Lulin |url=http://www.nasa.gov/mission_pages/swift/bursts/lulin.html}}</ref>
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