I discovered that AccuWeather.com offers forecasts for stargazing. It’s a nice quick glance at the week ahead, and it showed me that tomorrow, Thursday, and Friday were rated a “1″ (poor). Today was a “9″ (excellent) so I decided to go out as soon as it was dark enough.
My goal today was to again continue familiarizing myself with the overall layout of this section of the sky. Like yesterday, I was observing outside my front door. The conditions are certainly not optimal, with lights, buildings, trees, and cars. But not only will this be the easiest place for me to pop out for a few minutes to take in the sky, but also I want to get used to trying to pick out fainter objects under challenging conditions. My other goals were to study Perseus a bit more and to see if I could identify stars in a constellation I didn’t previously know.
Saturn, Mars, and Venus were all in the sky. Saturn and Spica make a nice bright pair, with Saturn looking softer and Spica harsher. Mars almost looks like a part of Leo, but its red color makes it a misfit among Leo’s stars. Venus is incredibly bright, with a magnitude of −4.35. It’s gorgeous, but its brightness was almost a distraction as I tried to study Perseus. Perseus was pretty low (altitude around 26°), so buildings blocked it and the thickness of the atmosphere and light pollution at that low elevation really concealed it. With difficulty, I could make out η Per (magnitude 3.75).
But I really struggled to see Algol (β Per, usual magnitude 2.05). I finally did manage to see it, but only if I kept my gaze about 10° to the side. I thought that perhaps because it was so much closer to the horizon (altitude around 18°), that was why it was so dim. But looking at my charts later, I read that Algol is not a single star, but rather a triple-star system (Beta Persei A, B, and C). From our point of view on Earth, we are in the same plane in which β Per A and β Per B orbit, so periodically the dimmer β Per B eclipses the brighter β Per A. According to Wikipedia, “Thus, Algol’s magnitude is usually near-constant at 2.1, but regularly dips to 3.4 every two days, 20 hours and 49 minutes during the roughly 10-hour long partial eclipses.” I then found a page on Sky & Telescope that showed that there was brightness minimum today at 21:44 CDT (4/18/2012, 0244 UT), which was right around the time I was observing it. Fascinating! — I can’t wait to see it during a period of normal brightness to compare.
High up in the sky, close to the zenith (altitude 80°), I was able to make out 38 Lyn (magnitude 3.90). That’s the dimmest star I identified tonight. I was not familiar with Lynx, nor with the adjacent Leo Minor, nor with the two nearby stars (λ UMa and μ UMa) that are part of Ursa Major but far from the Big Dipper asterism. It took me a long time to figure out what stars I was looking at.
But one of the highlights of the evening was seeing a slowly moving point of light traveling just below Arcturus (α Boo) and ε Boo in Boötes. I recognized it as an artificial satellite, and described the path into the Voice Recorder app on my iPhone so that I could identify it later. With help from the fantastic site Heavens Above, I was able to identify it as Cosmos 2082 Rocket. NASA’s page informs us that it was a surveillance/military satellite launched by the former U.S.S.R in May of 1990.
Then, a few minutes later, I noticed another moving point, this time in Ursa Major. Again, with the help of Heavens Above, I identified it as Tiangong-1, a Chinese space module that’s a prototype for docking capabilities for a future Chinese space station. It was launched last September.
In retrospect, it wasn’t only chance that I happened to see those two artificial satellites. During the day, the sky is too bright to see practically any satellite. At night, the Earth is between the satellite and the sun; in Earth’s shadow, they’re dark. But close to dawn and dusk, the sun may be below the horizon for us, but a satellite is high up enough that it can still get hit by sunlight.