If you get a clear sky in the evening sometime in the next couple of weeks, look low in the west about 45 minutes after sunset for a moderately bright “star.” It's actually Mercury, the most difficult to observe of all the planets known to the ancients. Currently it sets more than an hour and a half after the Sun does, allowing at least a 30-minute window for observation if the western horizon is polite enough to remain unobscured. Maximum elongation—the time of maximum angle between Mercury and the Sun as viewed from Earth—occurs on May 14. Because we're still fairly close to the spring equinox, we have a much better than average chance to see Mercury after sunset. (I still intend to write a post explaining why.) For this reason I had high hopes this week that the Baked Planet's light could punch through the murk of a Cleveland sky. In two and a half years living here I've been able to spot Mercury only once.

I started looking at the first of the month. My viewing log, if I kept one, would look something like this:

May 1: Forgot to look.
May 2: Rained out.
May 3: Rained out.
May 4: Not rained out but might as well have been. Haven't seen the Sun for yonks.
May 5: The sky was 95% clear at sunset. You'll never guess where the one patch of clouds had stationed itself until long after Mercury had set.

Tuesday promised a special treat: Mercury would be accompanied by a sliver moon, a mere three and a half hours after conjunction—if I had decent viewing conditions. Given my previous luck, and the storms that swept by all day, I didn't plan to even bother looking, but I'm glad I checked around 9:15 PM:



Here we see a 36-hour sliver moon with Mercury below and slightly left, at a distance of about two degrees of arc (four times the width of the Moon's disk). I can't believe I took a picture this steady without a tripod: I couldn't find ours, so I grabbed a little folding table from inside, set the camera on top, and tilted it back until I had the desired view in the finder. It helped that I cranked the ISO all the way up to 1600: this image, snapped a full hour after the sun slipped behind downtown Cleveland, is a mere 1/13-second exposure. Below is a shot at full telephoto:



If you like these, you'll find Astronomy Picture of the Day truly enchanting. Although the caption doesn't say, this photo was clearly taken somewhere in Europe: the location of the Moon, and the angle of incident sunlight, suggest the time to be about an hour and a half before the conjunction, or about five hours before my own sighting. (If the camera is level, the location is also considerably more northerly than Cleveland, as revealed by the angle the sliver makes with the horizon at its brightest, pointing toward the Sun.)

I'm delighted whenever I can enjoy some decent stargazing around here. Even Seattle had better sky conditions, overall.

Tags: astronomy, sliver_moon