This is Dudley Observatory’s Skywatch Line for Friday, May 15, through Sunday, May 17, written by Sam Salem.
On Friday, Sun rises at 5:32am and sets at 8:12pm, the waning crescent Moon rises at 2:44am and sets at 1:16pm. In the southeastern sky on Friday morning, between about 4am and sunrise, the crescent Moon will appear three finger widths to the lower left of Mars. Saturn, Jupiter and Neptune will share the sky with Mars and the Moon, but dim and distant Neptune will not be visible without a telescope. Neptune, at magnitude 7.9, in constellation Aquarius, is fairly low in the east-southeast just before dawn begins. Mars, Saturn, and Jupiter, plus the yet-to-rise Sun, will nicely define the plane of our Solar System across the sky. The Moon’s five-degree orbital inclination allows it to stray by up to that distance from the Solar System’s plane, at this time, below it.
Mercury begins to creep up into evening twilight. Start looking for it very low in the west-northwest 20 or 30 minutes after sunset. It’s roughly 15 degrees lower right of Venus. Mercury is brighter than usual at magnitude –1.2. It gets a little higher and easier each evening. Mercury will pair up with Venus on Thursday, when they’ll be 1 degree apart. Watch in the coming evenings, as Mercury ascends, while Venus descends in the evening sky. Venus, at magnitude –4.7, in northern constellation Taurus, is the bright white “Evening Star” in the west during and after dusk. It’s still at its brightest but is moving lower day by day. Look upper right of Venus for Capella, almost two fists at arm’s length away. Much closer above Venus is Beta Tauri (El Nath), fainter at magnitude 1.6.
Little squarish constellation Corvus, the Crow, can be found in the south after sunset at this time of year. It’s not far from the bright star Spica, the only bright star in the constellation Virgo. Once you find Spica, you’ll recognize the constellation Corvus. It’s recognizable for its compact, boxy shape. Spica is supposed to represent an Ear of Wheat, held by Virgo the Maiden. In a dark-enough sky, it almost looks as if Corvus were a real crow, pecking toward Spica, trying to snatch the wheat.
The long, dim sea serpent Hydra snakes level far across the southern sky. Find his head, a rather dim asterism about the width of your thumb at arm’s length in the southwest. It sits upper right of Procyon, the brightest star due west, by about a fist and a half. The brightest star of Hydra is Alphard, his 2nd-magnitude orange heart, a fist and a half left of his head. Hydra’s tail stretches all the way to Libra rising in the southeast. Dim constellation Crater and brighter constellation Corvus ride on his back. Hydra’s star pattern, from forehead to tail-tip, is 95 degrees from end to end, longer than any other constellation.
Comet PanSTARRS (C/2017 T2) is at peak brightness this month, after passing perihelion, its closest point to the Sun, last week, reaching magnitudes 8 to 9. The best time to spot the comet this weekend is in the morning between midnight and moonrise, or after the sky darkens following sunset. Currently in the constellation Camelopardalis, PanSTARRS is always above the horizon for most U.S. observers. PanSTARRS is relatively easy to find using the bowl of the Big Dipper. Swing your telescope from Dubhe, the bright star that forms the upper right corner of the bowl, about 17 degrees northwest to spot the comet. In one week, New Moon will occur as the comet skims by the famous pair of galaxies M81 and M82 in Ursa Major, making it both easier to find. This comet is not expected to be visible to the naked eye, but might be visible through binoculars.