Stellar Vista Observatory Sky Report: May 25-31

Earthshine on the moon, photo courtesy Claude Schneider, St. George News

SOUTHERN UTAH The weekly Sky Report alerts people to what they can see in the night sky by simply stepping outdoors and looking up, perhaps only with a pair of binoculars.

The Sky Report is presented as a public service by the Stellar Vista Observatory, a nonprofit organization based in Kanab, which provides observational experiences for people to enjoy, appreciate and comprehend what we can see in our starry night skies.

A lone Mercury

The sole planet in the evening sky is little Mercury — an elusive planet that most people have never seen. It’s hard to see because it orbits close to the sun, so it never strays far from the sun and it can be seen only shortly after sunset in the evening sky or shortly before sunrise in the morning sky, and it’s always near the horizon. So the first thing you need this week and next is a clear view of the northwestern horizon unobstructed by hills or anything else.

To find Mercury, look just above the northwest horizon beginning at 9:15 p.m., as the sky is still growing dark. It looks like a bright star with nothing about its appearance to give it away. The star Capella is the same brightness as Mercury and is 20° to the upper right of Mercury and you don’t want to confuse the two. Good luck, and use binoculars if you have them.

The “old moon”

Earthshine on the moon, photo courtesy Claude Schneider, St. George News

The moon is back. It’s a slim crescent as the week begins and it reaches its first quarter phase — when it has traveled one-quarter of the way around the sky — on Friday the 29th, so you can watch it move eastward against the background of stars and grow “fatter” night by night.

On which night can you first spot it? You should be able to see it on Monday the 25th as the thinnest of crescents in evening twilight low in the northwest. It’ll be easy to see on Tuesday the 26th, and note that the two bright stars to the right of it are Pollux and then Castor, in Gemini the Twins. Two nights later, on Thursday the 28th, the bright star to the left of the moon is Regulus, the heart of Leo, the Lion.

While looking at the thin crescent moon early in the week note that, if you look closely and especially if you have binoculars, you can faintly see the dark part of the moon as well as the comparatively brilliant crescent. The bright crescent is in full sunlight, but the dark part is lit by sunlight reflected off the earth back to the moon. Just as the full moon lights the ground on the earth, if you’re on the moon when the earth is full in the moon’s sky, the earth lights the moon — and from earth you see what is poetically called “the old moon in the new moon’s arms’ and is properly called “earthshine”.

The best nights to see earthshine are the May 25 through May 27.

Brighten your day

Turning to the morning sky, the planets Jupiter, Saturn, and Mars are strung out in a line. Brightest is Jupiter, the “king” of the planets, and it’s brighter than any star so you can’t miss it. Saturn is as bright as the brightest stars and it’s 5° to the left of Jupiter. Remember that the width of your fist held at arm’s length is 10°, so the two planets are quite close and will remain close all year.

Mars is as bright as Saturn and it is 40° to the left of Saturn, and a bit lower. Jupiter rises first, at about midnight, but the best time to see all three is between 4 a.m. and dawn.

The weekly Sky Report is written by John Mosley, a retired astronomer who lives in Ivins and who serves on the advisory committee for Stellar Vista Observatory. Send questions and comments to [email protected].

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