Skywatch Line for Wednesday and Thursday,July 19 and 20, 2023
This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday,
July 19 and 20, written by Alan French.
The Sun rises at 5:34 A.M. on Wednesday and sets at 8:29 P.M. On
Thursday it rises at 5:35 and sets at 8:28. This Thursday has 11 minutes
less daylight than last Thursday.
The Moon was new Monday afternoon and is now in the early evening sky as
it moves toward first quarter. It will reach first quarter early next
Tuesday evening.
On Wednesday and Thursday nights, at 9:15, if you have a good view to
the west to west northwest, you’ll be able to see a slender crescent
Moon, Venus, Regulus, Mars, and, perhaps, Mercury.
Remember that sky distances are easy to measure. If you hold your first
three fingers together and hold them at arm’s length in front of the
sky, they span 5 degrees across their tips. If you hold a fist at arm’s
length, it spans 10 degrees across the knuckles.
Venus, in the west, shining at magnitude -4.4, will be just under 4 ½
degrees above the horizon. The star Regulus is a little less than 4
degrees above Venus, and reddish Mars is just under 6 degrees to the
upper left of Regulus. If the skies are hazy, binoculars may aid
spotting Regulus and Mars. From Venus the young crescent Moon, two days
old and just under 5% in sunlight is, at the 2 o’clock position and 8 ½
degrees away.
Relative to the Moon, Mercury will be at the 5 o’clock position and 6
degrees away. Because of its low altitude, Mercury will be the biggest
challenge to spot. With our innermost planet only 2 ½ degrees above the
horizon, you’ll be looking through a thick layer of our atmosphere,
increasing the chances the view obscured. Binoculars can increase the
chance of spotting Mercury.
By Thursday night at 9:15 P.M. the Moon’s eastward motion against stars
will have moved it up near Mars, with Mars 3 degrees to the Moon’s left.
The Moon will be a lovely crescent, 9.4% in sunlight. Venus will be
below and a little right of the Moon, only 3 ½ degrees above the
horizon, with Mercury 11 ½ degrees to its right and only 2 ½ degrees
above the horizon.