Skywatch Line for Monday and Tuesday, September 25 and 26, 2023
This is Dudley Observatory’s Skywatch Line for Monday and Tuesday,
September 25 and 26, written by Alan French.
The Sun sets at 7:00 PM, with night falling at 8:36. Dawn begins at 5:03
and ends with sunrise at 6:09.
A young Moon follows the Sun across the sky on Monday, becoming visible
toward the southwest as darkness falls. Look for a slender, crescent
Moon a little west of southwest at 7:30 PM, 9 degrees above the horizon.
By 8:00 P.M. it will be just 4 ½ degrees high, but will be against
darker sky. The visible face of the Moon will be 14% in sunlight. Look
for earthshine, the light of our nearly full Earth in the Moon’s sky,
faintly illuminating the rest of the Moon. The Moon will set at 8:31 PM.
On Thursday the Moon will be farther from the Sun and higher in the sky
as darkness falls, but because the ecliptic makes a steep angle with the
horizon, the Moon will only be a little higher in the sky at 7:30, lying
just under 12 degrees above the southwestern horizon. Its visible face
will be 21 ½ percent in sunlight. By 8:00 PM the Moon will be just under
8 degrees high and the earthshine more obvious. The Moon will set at 8:57.
Saturn rose at 6:04 PM, almost an hour before sunset, and is in Aquarius
and 18 degrees high toward the southeast at 8:00 PM. Its lovely rings
are visible in a telescope magnifying about 30 times, but better seen at
60 power. Our telescopic views of celestial objects are best when they
are high in the sky and we are looking through less of Earth’s
atmosphere. Saturn is now due south and highest at 11:20 PM, when it is
just under 35 degrees high from our northern latitude.
Brighter Jupiter, in the constellation Aries, rises at 8:52 PM and is
just over 22 degrees above the eastern horizon by 11:00 PM. Shining at
magnitude -2.7 it is easy to spot. Jupiter is due south and highest at
3:57 AM.
The view of Jupiter with any telescope will reveal its four largest and
brightest moons, Io, Europa, Ganymede, and Callisto. From our vantage
point, the moons appear to shuttle back and forth across and behind the
planet, visible as stars just east and west of the planet, roughly in a
line. Sometimes one or more will be invisible. A moon may be behind the
planet, passing in front of Jupiter and difficult to spot, or in
Jupiter’s shadow and too dark to see.
With steady skies and patience, a 60 power view of Jupiter will reveal
some detail on the planet. Dark bands on either side of the equator, the
North and South Equatorial Belts (NEB and SEB), are not hard to spot.
The famous Great Red Spot (GRS) pushes into the south side of the South
Equatorial Belt. When near the meridian the GRS is easiest, but can be a
challenge.
Venus is now in the constellation Cancer and rises before the Sun, first
appearing at 3:36 AM. If you are up in the hours before sunrise, look
for Venus, shining brilliantly at magnitude -4.5, in the east.