This is the Dudley Observatory Skywatch Line for Wednesday, April 4th, and Thursday, April 5th, written by Louis Suarato.
The 84% illuminated, waning gibbous Moon sets at 9:14 a.m., and rises again at 11:53 p.m., 80% illuminated, between the constellations Ophiuchus and Scorpius. Scorpius’ brightest star, Antares, can be found to the Moon’s lower right, while Jupiter shines to the Moon’s upper right. Look for Venus before it sets in the west at 9:07 p.m. below the Pleiades star cluster. Saturn and Mars rise in Sagittarius at 2:09 and 2:21 overnight, 2 degrees apart.
Two of the brightest stars in our sky are visible these nights. The brightest, Sirius, in the constellation Canes Major, shines at magnitude -1.45. Sirius is 8.6 light-years away, and this binary system contains two of the eight closest stars to our Sun. Its luminosity is 25 times that of our Sun, which combined with its close proximity, contributes to Sirius’ brightness. Look over the southwestern horizon around 9 p.m. for the brightest star in the sky. Orion’s belt points southward to Sirius. The second brightest star in the sky is Arcturus. Found in the constellation Bootes, Arcturus shines at magnitude 0.15, and along with Virgo’s brightest star, Spica, and Leo’s brightest, Regulus, these stars form the asterism known as the Spring Triangle. Arcturus is 36.7 light-years away and 25 times the diameter of the Sun, and 170 times as luminous. Look for Arcturus after 9p.m. over the eastern horizon. The stars forming the handle of the Big Dipper point down to Arcturus.
There’s a small, faint constellation above Arcturus called Coma Berenices. This constellation is comprised of three 4th magnitude stars forming a 45 degree angle covering 386.5 square degrees.When looking towards Coma Berenices, you are looking perpendicular to the disk of the Milky Way, and away from the stars and dust forming our galaxy, therefor providing the clearest view of galaxies outside of our own. This region contains the Coma Galaxy Cluster, and the Virgo Galaxy Cluster, each hosting more than 1,000 galaxies. It is also the home of 8 Messier objects. Also found within Coma Berenices, is a loose open star cluster known as Melotte 111, or the Coma Star Cluster. This star cluster is about 7.5 degrees wide, or three quarters the width of a fist held at arm’s length, and contains 40 brighter stars ranging from magnitudes 5 to 10. The brightest stars form a V-shape as Coma Berenices is rising. The Coma Star Cluster is 280 light-years away and is approximately 450 million years old. Look for Melotte 111 at the top of Coma Berenices, and to the east of Denebola in Regulus.