This is the Dudley Observatory’s Skywatch Line for Monday Tuesday May 3rd, and 4th, written by Joe Slomka.
The Sun sets at 7:59 PM; night falls at 9:51. Dawn breaks at 3:53 AM and ends with sunrise at 5:45.
The Last Quarter Moon rose at 2:21 AM in Capricornus, and appeared 48% illuminated and set at 11:41. Tuesday’s Moon, in Aquarius, rises at 2:58 AM, appears 30 arc-minutes in size, 38% lit and sets at 12:50 PM.
Mars rises, in Gemini, during daytime, is near minimum with 1.6 magnitude and a small 4.6 arc-seconds. By 8:30 PM, it lies about 40° above the southwestern horizon and becomes lower daily. Asteroid 4Vesta remains the only other easily visible solar system object, still riding the back of Leo. Vesta rose at 1:49 PM and shines with 7th magnitude. It is highest at 9 PM when it is due South and 64° altitude; Vesta sets at 4:07 AM.
Also, in the western twilight sky, the constellation Taurus (the Bull) poses challenges for the observer. Venus rises during daytime, blazes with minus 4th magnitude and appears about 10 arc-seconds in size. By 8 PM, it lies about 7° low; however, its brilliance should attract attention; it sets at 8:43. Brilliant Venus points to the other challenge object, Mercury. The elusive planet also rose during daylight, glows with minus zero magnitude, appears a smaller 6 arc-seconds, about 75% lit, 13° high and sets at 9:22 PM. Both planets hug the western horizon, require an unobstructed horizon and may need binoculars.
The pre-dawn eastern sky presents a dramatic scene. Saturn rises first in Capricornus at 2:20 AM, glowing with zero magnitude, and is moderately sized at 16 arc-seconds. Jupiter follows, rising in Aquarius, bright with minus 2nd magnitude and appears twice as large as Saturn. Neptune shares Aquarius, glows with 8th magnitude and only 2 arc-seconds. As mentioned above, the Moon rises at 2:58 AM. Tuesday, the early riser will witness Saturn, Jupiter and the Moon forming a close triangle. By 4 AM, both Saturn and Jupiter will be quite obvious and about 9° apart from the Moon; Neptune, dimmer, lies 23° below Jupiter and may be difficult to spot in the rapidly brightening sky. All three planets set during daytime.
Saturn is the showpiece of any star party. Saturn is not the only planet that has rings. Jupiter, Uranus and Neptune were discovered to display rings by space-borne probes. Now, a new member joins the club. Last year, the European Space Organization (ESO) announced that Chariklo, an asteroid, possesses rings. This was an accidental finding. The ESO had several observatories study Chariklo as it occulted (or eclipsed) a star – to determine its size and shape. When they studied the results, the star was occulted three times. First it flickered; secondly the asteroid blacked it out; thirdly, it flickered again. Astronomers deduced that two rings surrounding Chariklo caused the flickering. Chariklo is a Centaur asteroid; it is rock, enclosed by a fuzzy comet-like halo of gas. The occultation revealed that it is the largest Centaur – 160 miles in diameter.