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January 2004 Feature: Venus & Uranus

You simply can't miss the planet Venus in the evening. It's the brightest heavenly body to light up the nighttime, aside from the Moon. Its brilliance fills the southwest sky as darkness falls, and continues to do so till it sets beneath the horizon some two and one-half to three hours after sunset. When you see this dazzling orb for yourself, you won't have to wonder why it's named in the honor of the goddess of love and beauty.

At mid month, Venus, the brightest naked-eye planet, is your ticket to finding Uranus, by far the faintest. To see it, however, you must be especially sharp-sighted, and have a clear, dark sky free of light pollution. Otherwise, binoculars make Uranus quite accessible -- if you only know where to look.

That's where Venus comes in to play. On the evening of January 14, Uranus resides a bit less than one degree to the upper right of Venus; and on the evening of January 15, Uranus is found a bit more than one degree to Venus' lower right.

For some perspective on what constitutes "one degree," keep in mind that a binocular field spans about six degrees -- though the figure is variable, depending on your binoculars. For a ball park reference, the distance between the two planets is one-sixth the diameter of your field of view. Though binoculars usually show Uranus rather readily, the planet still looks like a dim star.

Venus and Uranus set about three hours after sunset. So it's best to start your Uranus quest as soon as it gets good and dark, while the two planets are still somewhat high above the horizon.

Measure for Measure

Venus is called our "sister planet," because it's nearly the same size as Earth -- being only somewhat smaller. Uranus, however, has a diameter exceeding Venus' by more than four times. For our purposes, we'll round it off to an even four.

That means if Venus and Uranus stood an equal distance from us, Uranus' diameter would look four times larger than Venus' diameter. And if Uranus lodged four times further off than Venus, the two planets would look the same size.

As it stands, however, Venus' apparent diameter at mid month appears to be four times greater than Uranus' apparent diameter. So if the two planets look the same size when Uranus is four times Venus' distance from Earth, then Uranus must be sixteen times further away when its diameter appears to be one-fourth the size of Venus' diameter.*

*Uranus' apparent disk size, on the other hand, is only one-sixteenth as large Venus'. To find the proportionate disk size, you always square the diameter (1/4 X 1/4 = 1/16).

copyright 2004 by Bruce McClure

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