Moon to Pass in Front of Star Cluster
Most people are unaware of the moon?s rapid movement against the background of the stars, but this week early risers will get the chance to witness this as the moon moves past a series of celestial milestones.
Once a month, the moon makes a complete trip around the Earth, going through its sequence of phases.
Back on July 22, the moon was new, in fact located exactly between the sun and the Earth so that its shadow fell across India and China, causing an eclipse of the sun witnessed by millions of people. By July 28, it had traveled a quarter of the way around the Earth, reaching first quarter. On Aug. 6 the moon was full, having traveled half way around the Earth, and this week, on Thursday, Aug. 13, it reaches the three-quarters mark: last quarter.
As the moon wanes towards new moon on Aug. 20 it passes a series of markers. Most spectacularly, on the morning of Friday Aug. 14 it moves directly in front of the Pleiades star cluster. This cluster is the brightest ?deep sky object? in the sky, readily seen with the naked eye even in the city. With binoculars it is a glittering jewel box. As the moon passes in front of it, the stars of the cluster will be covered by the leading edge of the moon (on the lower left) and uncovered by the trailing edge (on the upper right). Watch it for a few minutes, and you should see this celestial disappearing act.
The following morning, Saturday Aug. 15, the moon will have moved well away from the Pleiades, and will be surrounded on three sides: the Pleiades to the upper right, the planet Mars to the lower left, and the bright red giant star Aldebaran to the lower right.
By Sunday morning, the moon will have passed Mars and will be heading towards the brilliant planet Venus, to the lower left. The following morning it will almost have reached Venus.
This gives us a special bonus, the opportunity to observe Venus in a full daylight sky. Venus is frequently visible in broad daylight, but you need to look in exactly the right place. Your eyes also need to be focused far enough away to see Venus; most of the time when our eyes are relaxed they focus fairly close to us.
By starting with the moon, you get a double boost: your eyes will be focused correctly on the moon, and the moon will show you where Venus is in the sky. Specifically, next Monday morning look for the Moon between 9:30 and 10:00 a.m. local time. Face due south and sweep from the southern horizon up towards the zenith overhead. The moon will be quite high in the sky, close to overhead. Once you locate the moon, Venus will be about 4 degrees below and to the left of the moon, a bit less than the width of the three fingers of your hand at arm?s length.
Spotting Venus in daylight isn?t easy, and it may help to use binoculars at first. Once again, the moon gives you a target to focus on, and then you just need to move the binoculars slightly down and to the right to spot Venus. Usually once you can see it with binoculars, it?s much easier to see with the naked eye.
By the following morning, the moon will be well past Venus and sinking towards the rising sun, but you may still be able to catch a glimpse of it.
As you watch the moon on its travels across the dawn sky, be sure to pay attention to its rapidly waning crescent, which narrows noticeably from night to night.
If all these early mornings are too much for you, or your view is blocked by clouds, you can readily view this whole journey with Starry Night.
This article was provided to SPACE.com by Starry Night Education, the leader in space science curriculum solutions.
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