A PLANETARY GATHERING
Dr. Terry Goforth
Associate Professor of Physics, SWOSU
May 2002

So you've been hearing about the great planetary alignment this month. Perhaps you've had a chance to see it. Or maybe you're wondering what all the all the talk is about. Well wonder no longer, and don't worry, it isn't over yet.

All five "naked-eye" planets, that is, the planets that can be seen without the aid of binoculars or a telescope, are currently gracing the western sky just after sunset. Such a gathering occurs only rarely. The last time it happened was in May 2000, but the planets were too close to the sun for us to notice them. Prior to that you have to go back to 1940, and the next time it will happen is in 2040. If you haven't taken a look yet, do so. It's a once-or-twice-in-a-lifetime event.

This planetary party began in late April and will continue through the end of May. For a few more nights, all five planets will be visible (weather permitting), but Mercury will soon disappear in the sun's glare.

Positions of 5 planets in the sky on the evening of May 8, 2002

To describe the positions of the other planets, we'll use a standard amateur astronomer's trick and describe the separation of sky objects in terms of finger widths and hand widths. To make use of the descriptions, extend your arm so you are looking at your hand at full arm's length. (It may help to close on eye so you are sighting along your arm.) This works relatively well for persons with any arm length and hand size since longer arms usually have wider hands.

If you go out around 9 p.m., both Venus and Jupiter are easy to find. Jupiter is about half-way up from the horizon and almost due west. Venus is lower and farther north, but shines so brilliantly that you will probably see it first. The dimmer planets will emerge as the sky darkens over the next 10 to 15 minutes. Look below and left of Venus for Saturn. Currently Saturn is about 1 to 2 finger widths from Venus, but Saturn is "dropping" toward the sun while Venus is climbing higher in the evening sky, so the separation is increasing. You can watch these two planets move apart over the next two weeks.

A few minutes after Saturn becomes visible, you should spot dim little Mars. (Can you detect the slightly orange color?) On May 8, Mars is slightly above and left of Venus, less than a single finger width away. By May 10, Mars will have dropped below Venus, still hugging close to the brighter planet. Mars will continue its downward slide, but it will move away from Venus at a much more leisurely pace than Saturn. The fifth planet, and by far the most difficult to spot) is Mercury. Start by mentally drawing a line between Jupiter and Venus. Now continue down and right along that line. The distance between Mercury and Venus is about one palm width (four fingers), or about half the distance between Jupiter and Venus. Mercury too is moving closer to the sun and will soon disappear into the sun's glare.

May 13 offers a bonus–the appearance of the young crescent moon low on the horizon. Mercury will be about one finger width away to the left and slightly above the moon. By now, binoculars may give you a better view of Mercury. Saturn will have dropped toward the horizon noticeably, and Mars will be below Venus as well. On May 14, the moon will be very close to Venus. With the brightness of both the moon and Venus, you may need binoculars to spot Mars. For the next two days, the moon will climb toward and past Jupiter. You may also notice that the gap between Jupiter and Venus is getting smaller. Mercury is long gone, and Saturn is disappearing in the sun's glare by now. Mars is still high enough to see, but extremely dim.

In late May and early June, the gathering is dominated by Jupiter and Venus. This bright pair will approach each other, making a conjunction on June 3, when they will be separated by less than a finger width. At this time, Mars will be to the lower right and close to the horizon and difficult to find in the twilight. Above Venus and Jupiter will be the Gemini twins, Castor (whitish in color on the right) and Pollux (slightly orange or red, on the left). After June 3, both Mars and Jupiter will continue approaching the sun, eventually disappearing from the evening sky. Venus will rule the evenings throughout the summer, reaching its maximum separation from the sun on August 21 before beginning a slow, stately approach back toward the sun.

For more information and sky maps, check out the May, 2002 issue of Sky and Telescope, or visit their web site at skyandtelescope.com, and click on "Rare Dance of Planets." Information may also be found at spaceweather.com.

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Last update:  May 8, 2002