This is Dudley Observatory’s Skywatch Line for Friday, September 27, through Sunday, September 29, written by Sam Salem.
On Friday, Sun rises at 6:48am and sets at 6:45pm; the waning crescent Moon rises at 5:03am and sets at 6:37pm. On Friday, the Moon reaches perigee, the closest point in its orbit around Earth, at 10:24pm. It lies 222,328 miles away from Earth. New Moon occurs at 2:26pm on Saturday. Because the Moon reached its closest point to Earth Friday evening, residents in coastal areas can expect higher than normal tides for the next few days.
The Moon’s absence from the morning sky these next two weeks is an excellent opportunity to view the zodiacal light. The time around the autumnal equinox is the best for viewing the elusive glow before sunrise. It appears slightly fainter than the Milky Way. You’ll need a clear moonless sky and an observing site located far from the city. Look for a cone-shaped glow that points nearly straight up from the eastern horizon, shortly before morning twilight begins.
Jupiter, at magnitude –2.1, lies between the feet of constellation Ophiuchus. Jupiter is the white dot low in the south-southwest as twilight fades away. It’s a poor season for observing Jupiter with a telescope as the planet is now sitting at low-altitude and as it has shrunk to just 37 arc-seconds wide. Jupiter sets a few minutes after 10:00pm. Saturn, at magnitude +0.4, sits in constellation Sagittarius. It lies 27 degrees upper left of Jupiter. Below Saturn is the handle of the Sagittarius Teapot. Barely above it is the dimmer, smaller bowl of the Teaspoon. Saturn sets a few minutes after midnight.
Try to spot Uranus unaided this weekend. Uranus, at magnitude 5.7, lies in constellation Aries. The planet is well up in the east by 11pm and highest in the south around 3am.
On Friday, try to locate planet Neptune. The planet sits in constellation Aquarius. Neptune appeared at its best at opposition earlier this month, but its visibility hardly suffers this week. The outermost major planet lies in the southeastern sky once darkness falls and climbs highest in the south around midnight. Neptune glows at magnitude 7.8, which is bright enough to spot through binoculars if you know where to look. Find the 4th-magnitude star Phi (φ) Aquarii, which lies about 15 degrees east-southeast of Aquarius’ distinctive Water Jar asterism. On Friday night, Neptune appears just 0.6 degrees west-southwest of Phi Aquarii. When viewed through a telescope, the ice giant planet shows a blue-gray disk.
The band of the Milky Way is tough to see unless you’re far from the artificial lights of the city and you’re looking on a night when the Moon is down. If you do look in a dark country sky, you’ll easily spot the Milky Way. Notice that it gets broader and richer in the southern part of the sky, in the direction of the constellations Scorpius and Sagittarius. This is the direction toward the galaxy’s center. The Lagoon Nebula, also known as M8 or Messier 8, is a large gas cloud within our Milky Way galaxy, barely visible to the human eye under good conditions. Bring your binoculars and look for M8 a few degrees above and to the right of the Teapot asterism in the constellation Sagittarius. Visually about three times the size of the full Moon, the Lagoon Nebula is the largest and brightest of a number of nebulosities in and around Sagittarius. Look for the Lagoon mid-summer to mid-fall. In September, the nebula crosses the meridian as darkness falls, making it prime for early evening observations.