Lulin dating compaign: update on Jan. 31
Jan 31st
I drag myself out of bed again at 4:30 a.m. It's another very clear night, with limiting magnitude around 5.4 (using IMO method -- but this do not mean that tonight is better than last night, since last night I had to use a not-well located reference field as the cirrus block the favourite one). I get the 13-cm refractor out and set it up, but it takes me a little bit longer than last night to see the comet.
With a telescope, the sky quality seems to be slightly better than last night, the faintest star I have been able to see is TYC 6174-464-1 at 12.28 mag, but (26) Proserpina (12.5 mag) is still invisible. Galaxy NGC 5890 (at 12.6 mag) is only 10' away according to the map, unsurprisingly it's not visible, too. Tonight I have much more options on comparasion stars -- but the observation doesn't make me feel exciting. I estimate the total brightness of the comet to be around 7.3 mag using Morris method, with six comparasion stars at mag 6.17-7.97, while the coma diameter to be 7'. The comet's look does not change much except a 30" dense core run out tonight. Tonight's estimate is 0.5 mag fainter than that of last night, I think tonight's one is more reliable since only two comparasion stars were used last night.
Shortly before the astronimical twilight starts, I also give a try on NGC 5892, a galaxy about 3 degrees away at 12.0 mag, but with no luck. Seems its surface brightness is still too dim. I then shift back to Lulin and see it off in the twilight (still barely visible even after the nautical twilight started!).
I'm not sure when would the next dating occur. I'll be away for a three-week tour in the country soon, and the rainy season will begin at Guangzhou before I come back. I'll try if I can spot it with naked-eye when I arrive at Mt. Huangshan in mid Feburary.
Second dating with Lulin
Jan 30th
As Comet Lulin is now approaching the Earth, the questions such as "how is your comet" or "did you take look at your comet" frequently fly into my ears. When replying these questions, I'd love to refer the comet as "my girl", and a standard reply is "no, I haven't date with her since last August". What's more, for a co-activity with Lulin's "heaven" show, I let my hair grow to a record length, and promise to my friends that "I will make it up according to the appearance of Lulin's tails". But actually, up to now, I have no time to make it up, and to be honest, no idea on how to make it up. I used to keep my hair very short. (the "public" reason is that the Lulin's tails are generally not visible yet)
As several cold fronts went over the Pearl River Delta around the Chinese New Year's Day, the air quality had improved to a very remarkable level. On Jan. 27, the Air Pollution Index (API) of Guangzhou's downtown was even down to 14 (while the average API of the downtown area is around 70-80). The Astroweather Panel suggested the sky would be clear in the morning of Jan. 30, so I went to my house at the countryside for a 4-day stay on Jan. 28. The air quality there was even more surprising -- with API lower than 4. Such an excellent air quality is rarely seen in the well-polluted Pearl River Delta area.
When I drag myself out of bed at 4 a.m. in the morning of Jan. 30, the sky did cleared up, although not as that good as Astroweather Panel predicted -- there are still a few cirrus on the sky. I checked the values of a nearby meteorological station, the temperature is 9.8C, not very low yet. So I carried by 80-mm f/5 refractor out. Except the cirrus, the sky is remarkably clear, I estimate the limiting magnitude to be 5.1 with IMO method -- also a record for this observing site. I wait for a few minutes until the cirrus move away from Libra, then point the telescope to the area. I don't bring my laptop out -- I was always very lazy and would not bring my laptop to the telescope, until I admit I'm unable remember the exact location of the target I want to observe. But this time I get a bonus, a fuzzy ball appeared in my view within only half a minute. I went into my bedroom, check the finding map, and confirm it's indeed "my girl".
I moved my biggest telescope -- a 13-cm f/6.4 refractor -- into the observing field. The 13-cm has a much better quality than the 8-cm. I point it to the comet, and try to estimate the comet's brightness using Sidgwick method. I'm not a good visual comet observer, and there are not sufficient comparasion stars around the area, so the observasion may be of some errors. The first estimate is 6.1 mag, but shortly after that I find out the comet is just occulting with a 10.72 mag star (TYC 6175-46-1), so I wait until it moves away from the star and make a second estimate. The final estimate is 6.7 mag with coma diameter to be 7'. The comet is slightly elongated over the ecliptic. After observed the comet, I make some attempts to see how deep I can go. A 12.16 mag star (TYC 6175-765-1) is visible, although not easily, but an asteroid nearby (26 Proserpina, around 12.5 mag) can not be seen, so the limiting magnitude for the 13-cm refractor at this night should be around 12.2 mag.
The twilight appears and marks the end of observing, I watch a beautiful sunrise (I always get excited about sunrises and sunsets!) at the observing field before go back to sleep. The visibility is also very remarkable today -- the 50-km away Mount Apoliu is clearly visible in twilight over a small patch of "cloud-sea".
Comet C/2007 N3 (Lulin) on Jan. 5
Jan 8th
[Images Removed]
A total of nine images of Comet Lulin were taken by the Lulin 0.41-m reflector over the night of Jan. 5, and I used every of them to process three impressive images as you have seen above. The first one is a color image, combined from one Blue-band image, one Visual-band image and seven averaged Red-band image, a low-pass FFT (Fast Fourier Transfer) filter was applied to let more details run out. The second image was averaged from seven Red-band image, a suprising ion-tail to the left, at a length of about 15-20' (the width of the image is 38'), was turned up after the align-and-stack method. Low-pass FFT was applied as well. The third image was processed by the Larson-Sekanina Rotational Gradient method, and it enabled us to see the near-nucleis jets of the comet. At least nine jets were counted besides the ion and the dust tails, and this feature does not be presented on the Jan. 1 and Jan. 2 images. This might be caused by the decreasing distance from the comet to the Earth as well as the sun. All the images were reduced to 600x600 pixel to match the size of my blog, the origin size images can be viewed below.
Update on Jan. 14: Since a complaint about the publication of their images from Lulin Observatory was filed to me yesterday, I have removed all the images about Comet Lulin appeared on my blog, of those taken by the 0.41-m reflector but NOT in the course of Lulin Sky Survey. My profuse apologizes go to Dr. Z. Y. Lin, who is considered to be the legal user of the data; and to those who are involved, including those who had got my permission to use these images earlier. I'll continuously monitoring the comet and post anything new on my blog, while ensuring only data from Lulin Sky Survey (the program I'm now responsible for) to be publicazed in any cases when the material is involved with Lulin Observatory.
A most recent photo of Comet Lulin
Jan 2nd
[Image Removed]
After discovered by Chi Sheng and me on July 11, 2007, Comet C/2007 N3 (Lulin) was brightening gradually as it approach to the sun. Now it is around 7 mag, shining on the east at dawn. If the prediction is right, it will be around 4 mag on late Feburary, marked as the brightest comet in the year (among the so far known).
This image was taken on the night of Jan. 1 by the 0.41-m reflector at Lulin Observatory (the instrument that used to discover the comet), a total of three images under Johnson B/V and Cousins R were later aligned and combined by myself, to create a "color" image. Two tails can be seen, as the one to right (the dust tail) is an anti-tail, caused by our observing angle. The streak on the left is a man-made satellite. The background stars look strange as the comet moves when taking the series of images.
As the discoverer, I'm feeling lucky to see the comet which I detect it first among the human beings, is now on a significant brightness. However, at the same time, I'm also reminded with such a story -- a teacher once asked his student, "which island is the biggest island before the discovery of Australia?" "Greenland." Some replied. "It's still Australia. Whether our human beings discovered it or not does not do anything to the fact that it's the biggest island on the Earth." I think, I was, simply, spotted the comet before anyone else, and that's all. I was just lucky. Anyway, I'll observe the comet in the next couple of weeks exactly -- maybe, just with a little bit extra excitation -- as others may do. Happy observing in the International Year of Astronomy, guys!
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