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C/2012 S1 ISON with 10"RC f8 and 5Dmk2-sp2 January 31, 2013 Cropped | by hirocun
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C/2012 S1 ISON with 10"RC f8 and 5Dmk2-sp2 January 31, 2013 Cropped

It was a cold and calm night, though the seeing was bad as usual in this season here due to the strong jet stream over our islands.


The comet appeared to have a tiny dust tail toward the south east, though it located far away, near 5AUs from the Sun, just a little nearer than the orbit of Jupiter at the date. This phenomenon may be another evidence that the origin of the comet is not Kuyper Belt but Oort Cloud. The comet may have existed near the orbit of Jupiter in early era of the Solar system, and it entered nearer than the distance from the Sun for the first time in the history of the Solar system. The comet may be now experiencing higher temperature than ever before.


The comet is expected to be the great comet of the century or the centuries since The Great Comet of 1680, 1680 V1, which passed the perihelion at 0.00622 AU on November 18,1680. C/2012 S1 (ISON) will pass the perihelion at 0.01251 AU on November 28, 2013. The two comets resemble each other extremely in terms of the orbit elements, and their origin is said to be the same big comet. The difference is that two members of ISON, International Scientific Optical Network found C/2012 S1 far earlier to the perihelion, and we can enjoy the comet for a long period. We may be able to be witnesses of the comet of the century with slightly curved long tail in the following mornings after the perihelion on November 28, 2013 or even in the daytime around the perihelion as C/1965 S1 Ikeya-Seki, which passed the perihelion at 0.007778 AU on October 21, 1965.


The coma was imaged to be a little elongated probably due to the movement of the comet while the relatively long exposure for comets.


Earth distance: 4.08 AU

Sun distance: 4.98 AU


Equipment: Guan Sheng Optical 10" RC f8 with Telescope Service 2.5" flattener, OAG, Feather Touch Focuser, and EOS 5Dmk2-sp2 on Losmandy G11 Gemini 2, autoguided at a star with Starlight Xpress Lodestar Autoguider via GPUSB and PHD guiding


Exposure: 3 times 8 minutes at ISO 6,400

First exposure started at 11:21:11UTC, and the last one at 11:37:41UTC in January 31, 2013.


Here is a short timelapse movie and data.


Here is a star-oriented image, composed of all data with SiriusComp, showing drifted comet images.

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Taken on January 31, 2013