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The Shallow Sky

A daytime occultation

Akkana Peck


There aren’t many planets in the August evening skies. But early risers can watch lots of planets in the morning sky – and there’s an unexpected daytime bonus. Even stranger, it doesn’t involve the sun this time, and you won’t need a solar filter: it’s a daytime occultation of Venus by the moon.

On Monday, August 13th, starting a little after 1 pm, the moon passes in front of Venus. The RASC handbook lists the time as exactly 1pm, but XEphem and some web sources show Venus disappearing at more like 1:30. In any case, the most interesting part of this occultation will be the lead-up, while you can see both Venus and the moon at once.

The nearness of the moon makes it easy to locate Venus during the day, something that’s usually a bit challenging even with this bright magnitude -4 planet. And you’ll be able to compare the phases of the two objects: the slim crescent of the moon contrasted with the half Venus.

It’s a great excuse to set up a telescope or binoculars for a late lunchtime observing session and share some photons with your co-workers or anyone else who happens by. I’ve heard an amazing number of adults express amazement at the idea of seeing the moon during the daytime (even though they’ve undoubtedly seen it themselves at some point)! So seeing both objects, and their phases, should be a great conversation starter outside the cafeteria or local coffeehouse.

Of course, what goes behind must come out again: Venus should re-emerge on the other side of the moon some between around 2:30 and 3 pm.

Aside from daytime views, Venus is an object of the morning twilight this month. Mercury joins it in the dawn sky a week into August, and stays there for a couple of weeks before disappearing again by month’s end.

Jupiter doesn’t rise until after midnight and will be at its best just before dawn. It just figures, because this month is full of double shadow transits – too many to list. Jupiter also has an occultation this month, on August 11 – but only if you’re in Hawaii or west of there.

You wanted an excuse to go to Hawaii this month, didn’t you?

What about normal nighttime observing? Well, Mars and Saturn are visible in the early evening, setting around 10-11. Catch them as early in the evening as possible if you want a good view.

The only planets that are really well placed for true nighttime observing are the three outer planets, Uranus, Neptune and Pluto.

Uranus doesn’t rise until a bit after the sky gets really dark, so it’s best after midnight, while Neptune rises a bit earlier. during evening twilight. Pluto is well up by sunset, and transits after 10 pm, so it’s ideally placed – except that it only gets about 33 degrees up and is lost in a Milky Way field right next to the open cluster M25. So much for ideals! In fact, Pluto is so close to M25 that you’ll probably mistake it as a faint member of the cluster. Try comparing it with a photo of M25 and see if you can spot the intruder!


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