This month, backyard astronomers will be treated to several interesting events in the sky. Head out to a dark place and watch the show. Even without a telescope or binoculars, you can gain some wonderful insights into how our universe works. In this article, I will call your attention to the moon hiding some planets and stars, a planet moving backward, seeing a planet with the naked eye even though the planet was only discovered with a telescope, and "stars" that come out in the daylight.
On the night of September 10, the moon will "occult," or hide several stars in the Pleiades cluster. This will only be visible in darkness from eastern Asia, from Japan west to Tibet. Shortly after moonrise in Tokyo, at about 11:30 local time, the moon will enter the Pleiades (which is known as Subaru in Japan). Along the way, it will occult the stars Merope (23 Tauri, magnitude 4.18), Alcyone (25 Tauri, magnitude 2.87), and Atlas (27 Tauri, magnitude 3.63). It emerges from the Pleiades at about 3:20 AM on the 11th, local time.
On September 13, the moon will occult Mars. While a planetary occultation is a rare and wonderful event to see, unfortunately few of us will be able to see it. The occultation occurs in a narrow arcing band from Scotland up through northern Scandinavia, across northern Russia, and into central Siberia. The moon and Mars will be in daylight for most of this event, and it will only be seen in darkness from Polyarny, Russia, and southeastward into sparsely populated central Siberia. Elsewhere, the moon will be seen passing less than half a degree - the apparent diameter of the moon - south of Mars.
On September 16, the moon will pass rather close to Venus, just about 3 degrees (six moon-widths) to the south. This will be an excellent opportunity to see Venus in daylight. If the weather is clear, it should be easy to find the moon just about 28 degrees west of the sun. Look for Venus by drawing an imaginary line connecting the two "horns" of the moon and extending it about six moon-widths north of the moon. (North is "up" from the moon, in the Northern Hemisphere.) The exact time of the closest approach will depend on where you are, because the moon is close enough to the earth that people in different places see it in different positions relative to the more distant stars and planets. From eastern North America, it's at about 11:30 AM EDT.
If you've never seen Venus in daylight before, you may be surprised at how easy it is to see this "star" in the blue sky of day. The moon makes it easier to find, but once you see it, you may wonder why you never saw it before.
On September 24, the moon will occult the brilliant star Antares (Alpha Scorpii, magnitude 0.88). Again, this occultation will only be visible where few people live, in far eastern Siberia and nearby areas of the Bering Sea. Farther south, such as in Hawaii, the moon will be less than 4 minutes of arc - barely more than one tenth the apparent diameter of the moon - as the two set together at about 11:00 PM local time.
On September 29, the moon will be in conjunction with Jupiter. All through the night, you will be able to see these two brightest objects in the night sky marching westward together. Shortly before sunset, if the weather is very, very clear, you might try your luck at seeing Jupiter in daylight. It's not as easy as Venus, but it can be done. (I've done it, but only a couple of times in conditions similar to what we will have on September 29.) At magnitude -2.7, Jupiter is nearly as bright as it ever gets, and just bright enough to see in daylight in very clear, very still conditions. On the east coast of North America, the moon and Jupiter will rise together at about 6:30 PM EDT. It will be easy to see the nearly full moon. Look for Jupiter about two degrees (four moon-widths) south of the moon. By the time they set at about 2:15 AM EDT on the 30th, the moon will have moved to the east so that Jupiter will be nearly four degrees (8 moon-widths) west-southwest of the moon.
Mercury begins to make its appearance as a "morning star" in the last days of the month. There will be a beautiful gathering of "morning stars" each morning from September 26 through the 30th. At first, Venus is keeping company with the bright star Regulus (Alpha Leonis, magnitude 1.35), rising about two hours before the sun. An hour or so later, Mercury (magnitude 2.2) and Saturn (magnitude 1.1) make their appearance. As the days progress, Venus will move closer to the other two planets, while Mercury and Saturn move farther away from the sun. By the morning of September 30, Venus is rising an hour and 40 minutes before the sun, and Mercury and Saturn rise 20 minutes later than Venus. By then, Venus will have grown to magnitude -3.9, and Mercury will flare up to magnitude 0.9, much brighter than pale yellow Saturn, which was outshining it by a whole order of magnitude just a few days before.
This September will be a good month to try to see the planet Uranus with the naked eye. At magnitude 5.7, it is just about as bright as it gets, and just barely bright enough to be seen with the naked eye. It does require fairly good eyesight and very clear, still air and dark conditions, but it can be seen without a telescope. It's a bit strange that this seventh planet was not discovered until after the invention of the telescope, but it was regarded as just an uninteresting dim "star." Like any planet, it moves, but it moves so slowly that nobody noticed it until Sir William Herschel "discovered" it in 1781. So, you can try to see this pale little planet without a telescope this month, once the moon leaves the sky dark enough. After about the tenth of the month, it rises more than two hours before the waning moon. Uranus is about 35 degrees east of Jupiter, in the constellation Pisces. There are no bright stars nearby to help you find it, but look for it near the midway point of a line between Gamma Piscium and Iota Ceti, two 3.5 magnitude stars about 20 degrees from each other. There is a line of very dim stars pointing toward it. 27 Piscium (mag. 4.86), 24 Piscium (mag. 5.93) and 20 Piscium (mag. 5.49) point to the slow-moving planet on about the tenth of the month. If you can see this dim line of stars, you should have no problem seeing Uranus at magnitude 5.7. As the month progresses, Uranus moves slowly west of this line. By the end of the month, the waxing moon will begin interfering again.
This will be a good month to observe the retrograde motion of Jupiter. Most of the time, the planets move eastward with respect to the stars (though, of course, the Earth's rotation carries the planets and stars westward at a much faster rate). However, when one of the outer planets is nearly opposite the sun, the earth's faster orbit causes the planet to appear to move "backward" for a time as we overtake and pass the slower planet. That is what is happening to Jupiter right now. All through the month, Jupiter is rather near the 4.28 magnitude star Iota Capricorni. Night after night, you can see Jupiter getting closer and closer to this star, moving slowly to the west. On the night of September 22, Jupiter gets within 14 minutes of arc (half a moon-width) of Iota Capricorni, then passes to the west of the star. It was this complex movement of the planets, sometimes eastward and sometimes westward, that first gave Copernicus the idea that maybe the Earth itself was moving, too.
These are just some of the wonders you can observe if you just take a little time each evening, or in the quiet predawn before you start you busy day, to look up at the heavens.
Author Resource:-
Chuck Bonner is a lifelong observer of nature and author of books and articles on observing nature at first-hand, including "Noticing Nature," available at http://www.amazon.com/dp/1440477787, and editor of http://www.natureezine.com Check back here every month for Chuck's report of interesting astronomical phenomena you can watch in your own backyard.
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