This picture is easily one of the most significant and exciting astronomical images I have ever taken. For unknown reasons, Comet Holmes has both suddenly brightened and expanded in the past few days to a size where it is now far larger than the Sun and the largest object in our whole solar system! To put matters in perspective, the Sun has an angular size of 31.5 arc minutes or a little over half a degree. This image covers an area measuring 86×105 arc minutes. Comet Holmes has a coma that easily is over 86 arc minutes at the widest point while being 80% farther from the Earth than the Earth is from the Sun!! The Sun would have an angular size of 17.5 arc minutes if were 80% father from the Earth like the comet. This makes the actual size of Comet Holmes’ coma about five times larger than our Sun or around 7 million kilometers across!! (The comet expanded even much larger in the following days.)
Comet 17P/Holmes was discovered by the British astronomer Edwin Holmes in November 6, 1892. The comet is part of our solar system with an orbit that always resides between the orbits of Mars and Jupiter. During its 2007 return, Holmes unexpectedly brightened from an extremely faint magnitude 17 to about magnitude 2.8 in a period of only 42 hours. It became easily visible to the naked eye. This represents a change of brightness by a factor of about half a million and is the largest known outburst by a comet.
