Editing Crab Nebula (section)

===Other objects===
Very rarely, [[Saturn]] transits the Crab Nebula. Its transit on 4 January 2003 ([[UTC]]) was the first since 31 December 1295 ([[Old Style and New Style dates|O.S.]]); another will not occur until 5 August 2267. Researchers used the Chandra X-ray Observatory to observe Saturn's moon [[Titan (moon)|Titan]] as it crossed the nebula, and found that Titan's X-ray 'shadow' was larger than its solid surface, due to absorption of X-rays in its atmosphere. These observations showed that the thickness of Titan's atmosphere is {{cvt|880|km}}.<ref>{{cite journal |last1=Mori |first1=K. |last2=Tsunemi |first2=H. |last3=Katayama |first3=H. |last4=Burrows |first4=D. N. |last5=Garmire |first5=G. P. |last6=Metzger |first6=A. E. |display-authors=1 |title=An X-Ray Measurement of Titan's Atmospheric Extent from Its Transit of the Crab Nebula |journal=[[The Astrophysical Journal]] |volume=607 |issue=2 |pages=1065–1069 |date=2004 |doi=10.1086/383521 |bibcode=2004ApJ...607.1065M |arxiv=astro-ph/0403283|s2cid=8836905 }} Chandra images used by Mori ''et al.'' can be viewed [http://chandra.harvard.edu/photo/2004/titan/ here].</ref> The transit of Saturn itself could not be observed, because Chandra was passing through the [[Van Allen belts]] at the time.