Second dating with Lulin

2009年1月30日15时17分　 English Island, 观星手记　2条回复 | 2 Comments
2007 n3, comet lulin

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".