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The Sky This Week
U.S. Naval Observatory's Weekly Blog
The Teapot in the Milky Way
by Geoff Chester, USNO Public Affairs
24 August 2021
Messier 8, the Lagoon Nebula in Sagittarius
imaged with an Antares Sentinel 80-mm (3-inch) f/6 refractor
and a Canon EOS Rebel T2i DSLR from Morattico, Virginia
The Moon wanes in the morning sky this week among the faint stars of the autumnal constellations. Luna climbs northward along the ecliptic, ending the week among the rising stars of the Great Winter Circle. Last Quarter occurs on the 30th at 3:13 am Eastern Daylight Time. Look for the Moon between the Pleiades and Hyades star clusters in Taurus before dawn on the morning of the 30th.
It’s a bit hard to believe that the autumnal equinox is less than a month away, but if you’ve been paying attention to the times of sunrise and sunset you have noticed that the days are rapidly becoming shorter. During the course of the week sunrise occurs five minutes later and sunset occurs 10 minutes earlier, and the total length of daylight is just over 13 hours. We will lose another hour of daylight over the course of the next several weeks.
As the Moon drifts farther into the morning sky and evening twilight ends at an earlier time we can turn our attention to the striking panoply of the summer sky. If you are planning to have a final summer vacation trip to the beach or the mountains, this is the time to spend some quality time under the stars. From sites well away from city lights you can enjoy the sight of the summer Milky Way, which carves an amorphous arc across the sky from the northeast to the south. The southern reaches of the Milky Way take up much of the southern view of the sky and form a softly glowing background to many of the season’s most prominent constellations. When we look in this direction we are looking toward the center of our home galaxy, but we can’t actually see its bulging nucleus. Notice the dark incursions into the pale glow of these distant star clouds. These are areas of cold gas and dust that absorb the light of the galaxy’s distant heart. The star clouds that we are able to see are some 8,000 light-years distant, but the galactic center is another 20,000 light-years beyond the cloaking dark clouds. This is a wonderful area to sweep with a pair of binoculars or a low-power telescope; the softly glowing clouds resolve into a myriad of stars, and sprinkled among them are glowing gaseous nebulae and glittering star clusters.
One of my favorite asterisms crosses the meridian just above the southern horizon at 10:00 pm local time. Popularly known as The Teapot, it consists of the brightest stars of the constellation Sagittarius, the Archer. The teapot is fairly easy to trace out, especially if you can see the Milky Way. One of the galaxy’s brightest star clouds seems to emanate from the Teapot’s “spout” like a cosmic cloud of steam. Just below the “spout” is one of the sky’s best binocular treats. Messier 7, sometimes called Ptolemy’s Cluster, easily resolves into dozens of twinkling gems. Just above the “spout” you will find several bright knots that are also good binocular targets. The brightest of these is Messier 8, also known as the Lagoon Nebula. Here you will find a star cluster embedded in a cloud of glowing gas. This is an area of continuing star formation similar to the Great Nebula in Orion. It is a wonderful sight in a low-power telescope field. Continue sweeping northward above the lagoon Nebula to see dozens of other clusters and glowing nebulae.
Bright Venus continues to press eastward along the ecliptic, wending her way southward as well. This week she closes in on the bright star Spica, which she will pass in early September. She currently sets at the end of evening astronomical twilight, but as fall progresses she will begin to command a higher place in the sky.
Golden Saturn trails the Teapot across the southern horizon. The ringed planet lies among the dim stars of the constellation Capricornus, the Sea-Goat. The planet’s distinctive rings are easily seen in a small telescope, and larger instruments will show detail in the rings and the planet’s delicately striped orb set among a sprinkling of faint moons.
Jupiter appears shortly after sunset in the southeastern sky, and is outshone only by Venus in the southwest. The giant planet now dominates the overnight hours and presents another great target for the casual skywatchers. His four bright Galilean moons are visible inn binoculars, while a four-inch telescope will reveal the planet’s equatorial cloud belts. These dark belts are zonal intersections between jet streams in the planet’s vast atmosphere that move past each other at speeds approaching 1000 kilometers per hour. I’m very glad that I don’t live there!
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