SUNSET: 
1Grab your curiosity, and come along on this month’s Sky Tour. This month offers a chance to glimpse a dramatic coverup of the bright star Spica by the first-quarter Moon. You can also glimpse Mercury just after sunset — and Saturn very late in the evening.
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If you’re a planet junkie, this will be a challenging month for you. Although it’s possible to spot Mars, Jupiter, and Saturn before dawn, to do that you’ll have to be up very early, at least 30 or 45 minutes before sunrise — roughly 4:30 a.m. for most of us. And July will be a month with no planets in the evening sky, with two minor exceptions.
Sky & Telescope
During the first half of this month, you can look for Mercury very low in the west, still immersed in twilight, about 30 minutes after sunset. Try spotting the thin crescent Moon at dusk on July 8th, and then follow an imaginary line toward its lower right to locate Mercury. And Saturn is gradually transitioning to the evening sky; you’ll be able to see it rising in the east around 11 p.m. early in July and by about 10 p.m. by month’s end.
After the Sun sinks from view, look high the western sky for Arcturus, very bright and most of the way up to overhead. Over to its right is the Big Dipper, seemingly hanging by its handle in the evening sky. Almost directly below Arcturus, by about three times the width of your clenched fist held at arm’s length, is the icy-white star Spica. It’s the alpha star in the constellation Virgo, the Maiden.
Stellarium
Well to the left of Spica is the bright star Antares, the heart of Scorpius. Can you tell that Antares has a reddish tinge compared to icy-white Spica? Antares is a red supergiant, and it’s one of the largest stars known — almost 700 times bigger than our Sun. In fact, if you swapped in Antares for our Sun, it would take up all the inner solar system out to the orbit of Mars and then some!
Spica is one of only four very bright stars periodically occulted, or covered, by the Moon. (The other three are Regulus, Antares, and Aldebaran.) Each star has its own occultation “season,” during which these coverups can occur monthly for up to several years. Spica gets its turn on the night of July 13th, when you can watch the dark limb of the first-quarter Moon creep closer and closer until the star’s light is extinguished in the blink of an eye.
To find out when this cover-up takes place — and which of you in North America won’t have a chance to see — you can get the details by listening to this month’s episode of the Sky Tour astronomy podcast. In fact, our monthly romp across the nighttime sky is a great way to get to know the stars and constellations better. So please join me!
About J. Kelly Beatty
J. Kelly Beatty, S&T Senior Editor, joined the staff of Sky Publishing in 1974 and specializes in planetary science and space exploration. Learn more about him here.
Comments
Curt Renz
July 5, 2024 at 5:34 pm
During the July Spica occultation, The Moon will appear slightly wider than a waxing Half Moon, since it will have just entered the second quarter of its lunation.
The Moon is always in one of the four quarters of a lunation, and what's listed as FQ on calendars is the cusp marking the completion of the first quarter and the commencement of the second quarter. As Jean Meeus notes, a more proper term is eastern quadrature, i.e. 90 degrees east of the Sun geocentrically. An average of 17 minutes before that time the Moon displays geocentric dichotomy, i.e. a 50% illuminated Half Moon. Beware, some authors get these confused.
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