See The Crescent Moon Hide Venus This Afternoon

A gravel bar in the shape of a crescent formed in Lake Superior at the mouth of the Lester River in Duluth recently. Photo: Bob King

The Perseid meteors still have some spunk! Observers worldwide reported a sharp rise in activity between 9:30 a.m. and 12:30 p.m.  CDT (when it was dark in Asia) Sunday. Rates hit over 100 meteors an hour during that time. A good show was still in progress last night, finally tapering off some during early morning hours today.

Crescents are everywhere. I was shooting aerial photos for the newspaper about a week ago. As we flew along the shore of Lake Superior I was paying more attention air turbulence than anything else. The plane seemed impossibly delicate as it pitched this way and that in the wind and heat. I looked out the window to follow our progress and moments  later spotted the most perfect crescent moon – a gravel bar at the mouth of the Lester River northeast of downtown. The sight quickly took my mind off the bumpy ride.

Later this afternoon, sky watchers across much of North America will see Venus covered or occulted by the real crescent moon. Finding the moon will be a little tricky. If you live in the Midwest it’s only 20 degrees high (two fists held at arm’s length) in the western sky when it happens around 3:30 p.m. (CDT). East Coast observers will have a tougher time with the moon only a few degrees high.  Exceptionally clear skies are required to see a thin moon so close to the horizon in the middle of the day.

Venus will hover right above the edge of the lunar crescent this afternoon August 13. This view shows the scene from Duluth, Minn. when the moon will be 20 degrees high in the west at the time. Created with Stellarium

Mountain states and the West Coast have the easiest time of it. When the occultation starts between 1 and 2 p.m. Pacific time, the moon will be 40 degrees high in the western sky. Take along a pair of binoculars to help you find it. Look for the crescent about 45 degrees or 4 1/2 fists to the lower right of the sun.

Use this map and table from Sky and Telescope to find your city along with the time when Venus disappears behind the moon. Remember that the times shown are Universal or Greenwich Time. Subtract 4 hours for Eastern Daylight Time; 5 hours for Central; 6 for Moutain and 7 for Pacific.

Venus is tiny half moon tomorrow as seen in a small telescope. The moon will take about a half minute to completely cover it. Venus reappears on the other side of the moon at 4:22 p.m. for Duluth. Created with Chris Marriott’s SkyMap

Go out 10 or 15 minutes before the occultation to find the moon either with your naked eye or with assistance from binoculars. Venus should be very easy to see nearly pinned to the moon’s pale white sunlit edge even in small binoculars. A small telescope will show the planet as a small half moon. Because it’s tiny and near maximum brightness, it will probably stand out better than the paler moon.

You may even be able to see Venus with the naked eye. For easterners unable to watch the occultation, all is not lost. You can still use the moon to find Venus in the daytime. Go out an hour earlier,  find the moon and look one moon-diameter above it to see Venus.

The last widely observed occultation of Venus by the moon happened on the morning of April 22, 2009. Both were crescents at the time. Notice how much brighter Venus is than the moon. Photo: Bob King

The moon’s orbital motion will carry it closer and closer to the planet until it takes that first bite. Since Venus has an actual shape and size as opposed to stars which are pinpoints even in large telescopes, it will take the moon nearly a half minute to completely cover it. About an hour later, Venus will re-emerge from behind the moon. Those times are also in the table if you scroll further down.  For Duluth, Minn. the hide-and-seek starts at 3:31 p.m. with Venus reappearing at the other end of the moon at 4:22 p.m. Disappearance and reappearance times for several other cities are shown below.

A Venus-moon-hawk “conjunction” at 11:30 a.m. today Aug. 13 when the moon was 2 degrees from Venus. Once I found the moon, Venus was relatively easy to see with the naked eye. Give it a try yourself. Photo: Bob King

Many of us will be at work when the occultation happens. Don’t tell my boss, but I’m going to sneak out for a few minutes around 3:30 with my binoculars. It’s not often you get to see the moon occult a planet in the light of day.

* Dayton, Ohio at 4:40 and 5:32 p.m.
* Chicago, Ill. at  3:37  and 4:29 p.m.
* Grand Forks, ND at 3:27 and 4:22 p.m.
* Denver, Colo. at 2:35 and 3:40 p.m.
* Seattle, Wash. at 1:07 and 2:23 p.m.

2 Responses

  1. Edward M. Boll

    So if Martian rocks could be on Earth, could not earth rocks be on Mars? If there are any fossils on Mars I would think that they would be in the Earth rocks. The night time temps just seem too cold to sustain life there.

    1. astrobob

      Edward,
      Yes, there are probably Earth rocks on Mars – a wonderful thought. Let’s hope one of our robots (better, a human) comes across one one day.

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