Sunday, January 17, 2016

Chasing C/2013 US10 (Catalina)

A comet's journey through the end of 2015 and the beginning of 2016

The comet Catalina, first discovered in October 2013 by the Catalina sky survey, has become very popular these days as it is approaching its closest distance to Earth. On the 17th of January it will be at 0.72 AU (108,000,000 km; 67,000,000 mi) from us. To give an idea of how far (or close) this is, let me make a comparison: the solar light takes 8.3 minutes to get us while the comets light will take only 6 minutes at that point.  

I started to look for the comet some days after it crossed the celestial equator and therefore became visible in the northern hemisphere.

On November 23 of last year, I first tried to watch the comet. I brought a “pseudo-chart” done by myself and Stellarium mobile in my tablet as helping tools. At about 6:45 am λVir was high enough above the apartment buildings letting me go down to MZVir and HIP69970 and keep going about 1° more to get Catalina in my FOV. As I was waiting for the comet to appear the day cleared and the only thing I could see was a stellar like object that I could not confirm as the comet. Shortly after the observation while verifying information in Stellarium, I could almost claim I had seen the comet because the next star was magnitude 9.20 while the comet was at 7th magnitude.

I waited some days more until it was clear again and the morning of the 28th I went out at about 6 am to try my luck. There was no power in the apartment complex but the full moon was lightning up the entire sky. I set up behind a building to avoid the moon glare and once I spotted Spica it was a piece of cake to get to the area.  The route was Spica – κVir – λVir. I hadn’t brought a chart but only my tablet. I did not know where the comet was because the old Stellarium mobile version, but I knew it must be closed to λVir. I saw a blurry star at 14' of λ Vir and immediately I knew that it was the comet. It seemed like a glob with averted vision, but I could not see any tail even though earthsky had reported 2 of them. I first thought the comet was 6th to 7th magnitude by comparing it with the stars around, but that was a subjective appreciation since it was not a stellar object.  I watched as the sky cleared more and more to determine what could or what could not be seen. My last record at 7:03 am with an almost white sky was this: “I could see clearly λVir and HIP70011A with averted vision. The comet had disappeared altogether. HIP70011A has a magnitude of 8.00 according my Stellarium mobile so I can estimate that at least the nucleus of the comet is a little dimmer than 8.00.

On the first of December I saw it and sketched it once again. Nothing special on the comet’s view but a similar view compared with November 28.

Next visit to the comet was on December 19. The comet was still traveling through Virgo but this time it was above 30° over the horizon, high enough to avoid some dense low fog. I had the impression that the glow around the compact and dense nucleus appeared like a moon fish shape and first I thought I saw the tails but I could not confirm it and probably it was my imagination. It took me about 30 minutes of observing and sketching the area and then I searched for the globular clusters M5 and M3. Although I could not compare them side by side, I believed the three of them were shining with similar magnitude. Probably M5 was a little brighter than Catalina but M3 and Catalina were more like each other in brightness and size.  Later I had a look of M53, closer to the Zenith. It did not look even close to Catalina's brightness so I would say Catalina was around 6th magnitude.

After New Year’s, I decided to look again for Catalina. No longer in Virgo, it had crossed Virgo’s legs, passed at less than 1° from Arcturus on Bootes and on January 8th was almost half of the distance from Arcturus to Alkaid in Ursa Major.

The local news in my country was saying that the comet was visible with the naked eye.  I did not believe it, much, but I still wanted to check it from my Bortle 5 sky. I got up at 5:45 local time and brought just my binos with me. It wasn’t the best location because there were some street lights around. Looked at Bootes which was above 60 degrees over the horizon, I could trace the whole pattern with ease. 

I looked above the star γBoo where the comet should be at that time. I could detect something very dim and almost blurry but later confirmed with the binos it was the star A Boo of magnitude 4.80. Right above A Boo I could see a triangle shape pattern made by the stars AW CVn, 25CVn and HIP67210/HIP67250. I tried hard, even with averted vision, but definitely I could not see the comet with just my eyes. 
Then it was time to see it with the binoculars. It seemed like fuzzy ball with no big difference in size than what I'd seen before. I could not see a tail this time either. Stellarium mobile showed the comet to be Mag of 4.92. I compared the comet view with M3 and definitely it looked brighter and more compact than Catalina. I doubted Catalina's magnitude was 4.92, but be more like 6th Magnitude still.

My last observation was the 15th of January in the morning. I took my new telescope (I will talk about it in a later entry) with me in order to share some views with my wife. Catalina was right below Alkaid and seemed an easy target to try the 40mm plossl eyepiece I’d bought some days before. I spotted Alkaid with the red dot finderscope and then went down a little bit after I saw the fuzzy ball. At 37.5x it didn’t look too different than with the binoculars. Then I switched the eyepiece to get 166x and I did not notice a noticeable difference other than the size.

I made a collage of the 3 sketches. Actually, I can notice a difference in size and brightness as the time passed and the comet was closer to Earth. Nothing that I measured in my observation notes so it could be a product of the external conditions of observation.

I hope you can enjoy these extended Comet observation log and wish you Happy New Year 2016 and the best skies at night.


Edited by Jennifer Steinberg (editor in chief)


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