This is the Skywatch Line for Monday and Tuesday, May 7th and 8th.
The Sun sets at 8:02 PM; night falls at 9:57. Dawn begins at 3:46 AM and ends with the Sun rising at 5:40.
Two bright planets illuminate the evening sky. Venus, in Taurus, blazes with minus 4th magnitude about 19º above the western horizon. In binoculars or telescope, it appears about 87% lit. Venus sets at 10:32 PM.
Jupiter has already risen in the eastern constellation of Libra. It glows with minus 2nd magnitude and appears about 5º high at Civil Dusk. Jupiter is highest and best at 12:57 AM and sets after sunrise. Jupiter reaches opposition at 9 PM on Tuesday, when Jupiter, Earth and the Sun line up; it is also at its biggest and brightest of the year. Monday, telescopic viewers can also see the Jovian moon IO begin to cross the planet’s face at 10:56 PM, followed by the moon itself two minutes later. IO’s shadow leaves Jupiter at 1:06 AM on Tuesday, followed by IO at 1:07. Sky watchers can see the Great Red Spot at 9:25 PM Tuesday.
The asteroid 4Vesta inhabits Sagittarius. Tuesday, 4Vesta is stationary, meaning that it apparently stands still before heading westward. Sixth magnitude 4Vesta is well placed for telescopic viewing, bracketed by Messier objects M24 and M25; it appears as a tiny ½ arc-second in size. The Messier objects are a brighter 4th magnitude. 4Vesta rises at 11:15 PM and is best observed at 4:13 AM.
Saturn shares Sagittarius with 4Vesta, rising at 11:51 PM and glows with zero magnitude. Saturn is quite near globular star clusters M22 and M28. Saturn is best observed at 4:29 AM, when it is 24º high, revealing its famous rings. Saturn begins a train of planets in the brightening pre-sunrise sky.
Mars, now rapidly brightening, is the third object in Sagittarius. Shining at minus 1st magnitude, it appears about 12 arc-seconds in size and 89 % illuminated. Mars is the brightest object in Sagittarius.
The last quarter Moon, on Tuesday, rises at 2:21 AM, glaring at minus 10th magnitude and appearing about 48% lit. Wednesday’s Moon rises in Aquarius at 2:53 AM, slightly dimmer and 38% lit.
Neptune shares Aquarius with Wednesday’s Moon. Neptune rises at 3:21 AM, and gleams with 8th magnitude. The blue-green tinted planet appears 2.2 arc-seconds in size. An observer should try before the sky becomes too bright. By Civil Dawn, it is about 18º high in the East.
One of the common astronomical clichés is that Jupiter’s Great Red Spot has been continuously observed for three centuries. The Spot has been known to change. For example, it was closer to a salmon color, but recently reported to redden. The Spot was 2 ½ times larger 100 years ago. When measured in the 1800’s, the storm was 25,000 miles wide. Today, it is about 9,600 miles long and 7400 miles wide. Astronomers report that wind speeds are increasing. The Great Red spot now has 300 miles-per-hour winds, up from 250. Like an ice skater, it spins faster as it gets smaller. Some scientists speculate that, by 2050, it may be known as the Great Red Circle. While an unfiltered telescope reveals details of its chaotic weather systems, use of blue or green filters can enhance details.