Neptune By Way Of The Moon

This binocular view shows the moon with Neptune just 2° to its north (right) as you’d view it this evening around 6 p.m. CST. You can star-hop from the moon to the naked eye star Lambda (λ) in Aquarius. Neptune makes a nifty equilateral triangle with Lambda and a fainter star above it. Stellarium with additions by the author

Tonight, the crescent moon will look about a wide as an unclipped fingernail. You’ll spot it right away in the southwestern sky at dusk, high and bright. Just 2° (four moon diameters) to the moon’s upper right lurks another member of the solar system, the planet Neptune. The two are in conjunction tonight in the dim constellation Aquarius.

A small dot in a telescope, if we could plop Neptune in place of the moon, it would look about this big in our sky. The planet is 30,600 miles across or about four times as big as Earth. Its blue color comes from methane gas in its mostly hydrogen and helium atmosphere. Roscosmos

Small telescope owners can use the lunar crescent to find their way to the planet, which looks like a blue-hued star at low magnification. But if you up the power 150x or higher, Neptune will show a small disk compared to the pinpoint stars. It’s always nice to have the moon around to help us find the dimmer planets. A 3-inch telescope will show Neptune easily.

Want to test your observing skills? Try finding it in binoculars. 7×50, 10×50 or 8×40 glasses will typically show the planet from outer suburban areas. With the moon nearby tonight, the extra light will make spotting the planet a little more challenging. Mounting the binoculars on a tripod can really help in seeing fainter stuff, but if you can’t do that, brace yourself against a door or wall and hold them as steady as you can. Focus on the stars and avoid looking directly at the moon to preserve your night vision.

This map shows the moon’s phase this evening (Jan. 20). I’ve labeled the two prominent “seas” and a few of the best craters. NASA

Did I just say avoid the moon? Please don’t do that. After you’ve attempted Neptune turn back to the moon. Most binoculars will show a line of craters along the inner curve of the crescent, the line separating the sunlit part of the moon from the part that’s still in darkness called the terminator.

2 Responses

  1. EdWard M. Boll

    I guess ome day. I should look for it some night.. My 20 powr binoculars may show it faintly. And my scope is just too wobbly.

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