Skywatch Line for Wednesday and Thursday, September 6 and 7, 2023
This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday,
September 6 and 7, written by Alan French.
The Sun rises at 6;25 A.M. on Wednesday and sets at 7:21 P.M. On
Thursday it rises at 6:26 and sets at 7:20. This Thursday has 19 minutes
18 seconds less daylight than last Thursday.
The Moon was full on August 30 and, reaching full soon after perigee,
its closest point to Earth, was this year’s largest full Moon. If you
missed it, you’ll have two chances to see such “supermoons” in 2024, on
September 18 and October 17.
The Moon will reach last quarter, having completed three-quarters of its
trip around the Sun since new, at 6:21 P.M. EDT on Wednesday, September
6, and then will start moving toward new. The Moon, its visible face
just under 48% in sunlight, will rise at 11:01 P.M. Wednesday night. On
Thursday it will rise at 11:47 P.M. and will be 37.4% illuminated. The
Moon will reach new on Thursday, September 14.
The earlier evening hours are dark and moonless. At 9:30 P.M. the large
asterism known as the Summer Triangle stands high in the southern sky.
Altair, the brightest star in Aquila, the Eagle, is the lower of the
three stars, lying just east of due south and 56 degrees above the
horizon. The other two stars straddle the zenith, with the brightest,
Vega, 12 degrees to the west and Deneb 12 degrees to the east. Deneb
marks the tail of Cygnus, the Swan, and Vega is the brightest star in
Lyra, the Lyre.
If you have clear skies and are away from city lights, where the skies
are dark, you’ll see the Milky Way, a hazy band of light, the combined
light of unresolved stars, arcing upward from the south southwest
through Aquila and passing above Altair. It then runs along Cygnus and
then toward the northeast and Cassiopeia. Under dark skies it is a very
impressive sight, even better if you have your eyes time to get used to
the dark. Under such conditions it can be fun to explore the Milky Way
with binoculars, any binoculars will show more than can be seen by eye.
A reclining lawn chair can provide for comfortable explorations.
If you’re up early Thursday or Friday morning you can watch the
International Space Station (ISS) glide across the morning sky.
On Thursday morning the ISS will rise from the west northwestern
horizon, headed southward, first visible around 5:48 A.M. It will be due
west and 43 degrees above the horizon just after 5:50. The ISS will pass
just below bright Jupiter, high in the southwest, at 5:51:20. Its path
will then take it close to Rigel, in Orion, and past Sirius, in Canis
Major, before it vanishes below the southeastern horizon at 5:56.
Friday’s pass of the ISS is earlier, under darker skies, and higher,
essentially passing overhead. When it first comes up in the northwest,
along the neck of Cygnus, the ISS will be the Earth’s shadow and
invisible. Watch for the space station to emerge from the shadow and
come into view as it moves along the southern side of the Swan’s tail
just before 5:01 A.M., when it will be 22 degrees high
The ISS will pass by the familiar W of Cassiopeia just after 5:02 and
then pass through Pegasus. Just after 5:03 its path will take it by the
pentagon of stars outlining Auriga. It will then pass above Orion and
then down to the southeastern horizon, vanishing after 5:07.