This is the Skywatch Line for Monday and Tuesday, March 4th and 5th.
The Sun sets at 5:48 PM; night falls at 7:22. Dawn breaks at 4:51 AM and ends with the Sun rising at 6:25.
The evening sky is basically unchanged from last month. Mars is still the only easily observed planet. In Aries, the Red Planet appears about 92% illuminated and shining with 1st magnitude. Mars continues its eastward motion, seemingly stationary against the stars; however, it daily sinks a little lower. Mars sets at 10:50 PM. About 12º to Mars’ lower right is Uranus. Sharing Aries with Mars, this gas giant planet shines with 6th magnitude but is a tiny 3 arc-seconds in size in our instruments. It, too, slowly sinks in the western sky and is becoming difficult to spot. Binoculars or telescope are helpful. Uranus sets at 9:42 PM.
Mercury also appears to be stationary in Pisces. However, its 22% lit surface rapidly thins and along with its 10º altitude in the West makes spotting it increasingly difficult also. Mercury sets at 7:11 PM.
The Moon turns “New” Wednesday morning and is absent from our sky on both nights.
The absence of the Moon makes comet hunting easier. Comet Wirtanen still inhabits Ursa Major (The Great Bear), but fades to 10th magnitude. It is located between the stars Theta and Lambda and best observed at 10:45 PM. Comet Iwamoto is located in Auriga, near the star Iota. It is brighter with 7th magnitude and sets at 2:50 AM. Finder charts for both are available from several online websites.
The pre-Dawn sky is alive with bright planets. Jupiter rises first, at 1:58 AM, in Ophiuchus. It glows with minus 2nd magnitude and is a large 36 arc-seconds in size. By first light, it is about 21º high in the East. It is high enough for sky watchers to start following its famous Galilean moons. Tuesday marks the 40th anniversary of Voyager#1’s flyby of Jupiter. Today, Voyager#1 has left the Solar System and is about 13.4 billion miles in deep space. It still communicates with NASA, but its messages take over 20 hours to arrive at its home planet. It now studies cosmic rays.
Saturn lies about 25º to Jupiter’s lower left, in Sagittarius. It shines with zero magnitude and is about half Jupiter’s size in our telescopes. Saturn rises at 3:45 AM and, by Dawn, is about 9º high. It, too, is high enough to appreciate its beautiful ring system.
Venus hugs the eastern horizon. Rising 4:39 AM in Capricornus, it blazes with minus 4th magnitude, appears about 74% lit and almost as large as Saturn in our telescopes. However, its low 2º altitude requires an unobstructed eastern horizon.
By 10 PM, a bright orange star glows low in the East. This is Arcturus, the brightest star of the constellation Bootes. It is variously translated as “Herdsman” or “Bear Driver.” Arcturus is the closest giant star to Earth. Its diameter is 26 times larger than the Sun, but is only four times heavier. Arcturus is an older, bloated, cool star that has probably stopped fusing hydrogen and is consuming helium instead. Arcturus is famous for a few reasons. Proper motion is a star’s actual movement through space. Sir Edmond Halley, of comet fame, discovered the star’s proper motion in 1718. The 1933 Chicago World’s Fair used the light from Arcturus to officially open the event. At that time Arcturus was estimated to be 40 light-years distant, the time of the 1893 Chicago World’s Fair. We now know Arcturus is slightly closer, about 37 light-years away.