C/2012 S1 ISON with RH200mmf3.0 September 16, 2013UTC
The comet appeared with yellowish white dust tail with length about four arcminutes and green-tinted halo in the constellation Cancer. The greenish halo was visible in G-channel widely, B-channel slightly, and R-channel nothing in the sea of noise, thus it may be indicating there already exists molecular C2 and emitting 516nm in Swan Bands of diatomic carbon. The entity would be confirmed with spectral observation and analysis of the comet, though the signal might be still obscure and unclear for a while.
The location of the comet was 1.9 AUs from the Sun and 2.6 AUs from the Earth at the night, 72 days before the perihelion passage at 0.0125 AUs from the center of the Sun according to the current prediction. The comet looks to be already in "frost line" area near the orbit of Mars, which the comet will fly by at 0.07 AUs from the planet on October 1, 2013. This imaging was done 15 days before the fly by.
"Outgassing Behavior of C/2012 S1 (ISON) from September 2011 to June 2013" by Meech KJ et al sept. 10, 2013. Beautiful images with Gemini North 8m scope and R magnitude curve (radius 15") are in it. ( link below courtesy of Karen Meech )
Chris Schur performed spectral analysis of the comet and detected C2 emission lines on October 12, 2013. ( link below courtesy of Chris Schur )
This 1314 x 976-pixel frame is cropped of 5634 x 3753-pixel full frame. If I could use an optics with focal length about 2.5m, I may be able to take a frame of this scale.
Though the dark window was short, about an hour after moonset and before the beginning of twilight, the night was the last chance for imaging of the comet in the moon cycle. I was lucky enough to take this frame just after the passage of big typhoon Man-Yi. The passage was about twelve hours before the session at the site. The road to the site was wet and full of fallen leaves and twigs, and I could find some fallen small rocks. There came no clouds, and transparency was extraordinary, though seeing was very bad probably due to the typhoon.
Next chance for imaging of this comet will begin on 4th or 5th October, 2013 with no moon interference.
equipment: Officina Stellare Riccardi-Hondars Astrograph D=200mm f/3.0 "Veloce," optical designed by Massimo Riccardi and Canon EOS 5Dmk2-sp2, modified by Seo-san on Losmandy G11 equatorial mount, autoguided with hiro-design simple off-axis guider, Starlightxpress Lodestar Autoguider, and PHD guiding
exposure: 3 times 4 minutes at ISO 1,600 and f/3.0
The first exposure started at 18:43:13 and the last one started at 18:51:33UTC, two minutes after the beginning of twilight on September 16, 2013.
site: 1,400m above sea level at lat. 36 46 44.7 N. and long. 139 27 01.5 E. in Nikko, Tochigi