This is Dudley Observatory’s Skywatch Line for Friday, July 17, through Sunday, July 19, written by Sam Salem.
On Friday, Sun rises at 5:33am and sets at 8:30pm; Moon rises at 2:38am and sets at 6:02pm. In the eastern pre-dawn sky on Friday, the waning crescent Moon will be positioned less than three finger widths to the upper of the bright planet Venus. Both objects will appear together in binoculars until sunrise. In a telescope, Venus will show a crescent phase similar to the Moon’s.
For a short period before dawn on Sunday, if you have a clear view of the east-northeastern horizon you might be able to spot the very slender crescent of the old Moon sitting four finger widths to the left of Mercury. Start your search after about 4:45am, when the pair will sit less than a fist’s diameter above the horizon.
Comet NEOWISE has moved into the evening sky and is climbing higher each night. For the northern U.S., the comet is circumpolar and visible all night long this week. It reaches maximum northern declination, of +48 degrees, on Monday when it never dips below the horizon for locations north of latitude 42 degrees North. While the telescopic view reveals additional structures in the coma and intensifies the comet’s colors, only binoculars comfortably reveal the full breadth of the tail. The dust tail extends, currently, even beyond the typical 5.5°–6.5° binocular field of view, while the fainter ion tail unfurls to more than 15°. You can start looking as early as 9:45–10 p.m. low in the northwestern sky. The Big Dipper will help in guiding where to look. For exact location, use “Sky and Telescope” map in the link below.
Before you look for the comet be sure to focus the binoculars on a bright star or planet first. That will make the fuzzy comet easier to spot. The comet will fade in the coming weeks. It’s expected to drop to 3rd. magnitude by Saturday, and to 4th magnitude by next Saturday. However, it’s also climbing higher and higher in the evening sky, which will partially offset its dimming.
In the east after dark on these July evenings, look near the horizon for Altair, the brightest star in the constellation Aquila the Eagle. This is the bottom star of the Summer Triangle. It’s the last of its three bright stars to ascend over the horizon. You will recognize Altair by the two fainter stars on either side of it. The Great Rift of the summer Milky Way passes through the Summer Triangle, between the stars Vega and Altair. In dark skies in June, July and August, you can see rich star fields with your binoculars on both sides of the Great Rift.
Friday marks the 45th anniversary of the Apollo-Soyuz link-up in Earth orbit, the first international space mission. Three American astronauts aboard an Apollo capsule and two Soviet cosmonauts in a Soyuz spacecraft launched hours apart from the U.S. and Kazakhstan on July 15, 1975. Two days later, the craft rendezvoused. The spacecraft hard docked at 12:12 P.M. EDT and about three hours later, at 3:17 P.M. EDT, the crews met.