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Object Data: Comet Lulin (also known as C/2007 N3) shown here on the night of February 24/25, the time of its closest approach to earth, is a 'new' comet, meaning that it has not been catalogued before and as far as we know has not orbited the sun before (it may have done so but with a thousand year orbit would have been invisible to unaided human eyes of the time). Comet Lulin was first discovered by a Chinese astronomer on July 11, 2007, on images taken by Taiwanese astronomer Chi Sheng Lin at the Lulin Observatory, giving the comet its name. It is a comet with an extraordinary tail; owing to a fairly rare alignment of its orbital plane with the earth's, the ion tail appears to 'swivel' round the coma as seen from the earth's perspective. Early images showed this as an 'anti tail', pointing in the opposite direction to the dust tail, whereas in this photo it is seen pointing 'upwards' - in reality it is pointing away from us (thus appears rather short), and away from the sun (the ion tail always points away from the sun whereas the dust tail always follows the path of the comet). Another unusual aspect is the strong green colour of the coma - this is due to the ionization of gases (ionized cyanogen and diatomic carbon) expelled from the coma by the sun's radiation. In this image the dust tail can be seen extending 2.5° towards the lower left. The entire field covers approximately 3.2°from East to West and is centered on 11h 02m 16s +05°58' 42" in Leo.
Date: 2009-02-25 / 01:09 GMT
Location: Southern France
Conditions: Calm, transparency=8, seeing=6
Optics: Tak FSQ 106ED at f/5.0
Mount: AP 900 GTO on Portable Pier
Camera: SBIG STL-11K, SBIG LRGBC filter set, -30°C
Guiding: Integral STL-11K autoguider
Exposure: RGB only binned 2x2; 20x 120 : 78 : 120
Processing: Image acquisition and initial processing using Maxim DL, subsequent processing in Photoshop.Notes: A selection of the original 20 images was separately processed for the sky background and the comet using SD Mask and the comet image layered on the sky background image using lighten mode.
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