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Sunday, August 03, 2008


Now That's a Thin Crescent Moon

The start of the Planet Dance was last evening. Hughie was kind (although it poured rain on EdlestOnes soccer match) and the sky cleared in the evening so I could see the line-up. If you enlarge the image on the left by clicking it, you can see Mars, Saturn and Venus (Regulus is too dim to be seen in the thumbnail, but you can see it as the dot between Saturn and Venus on the full-size image).

But where is the Moon? It's below Venus! But you can't see it!

One thing I hadn't counted on was the thinness of the Moon, at only 22 hours past new and 10 degrees from the Sun the crescent was only 1.2% illuminated and stuck deep in the twilight. Although this is not the most extreme crescent Moon, it made it dashed hard to see, and near impossible to photograph.

It's very likely many people missed the Moon altogether, and were standing around saying "what the heck was he talking about. There is no Moon?"

In the image below you can see the crescent Moon as a faint line near the bottom left of the thumbnail. Click on the image to enlarge it to see it in more detail (such as it is). The Moon was relatively hard to see at civil twilight (30 minutes after Sunset), but once you were used to it it was fairly easy to watch. Photographing it was a real pain though.

Not as much of a pain as trying to image the Moon 3hrs and 27 minutes before new. Catching extreme crescent Moons is a bit of a past time with some astronomers, you can see a list of records here. If you are interested in trying to see the thinnest crescent Moon, you will need a really flat, unobscured horizon (like the sea, or desert plains. It works even better if you are up a mountain overlooking a flat horizon). I have the sea for my western horizon (if I walk down the beach), so I might have a go.

If you are interested in seeing really thin crescent moons this article gives you lots of hints, and Steve Saber publishes tables of timings of thin crescent Moons. He also has some handy hints on observing thin crescents. So why not have a go?

(Of course, tonight is cloudy, so I miss the Moon next to Saturn)

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