This is the Dudley Observatory Skywatch Line for Wednesday, June 6th, and Thursday, June 7th, written by Louis Suarato.
Wednesday evening begins with Venus cradled in the arms of Gemini above the western horizon. The bright star to the upper right of Venus is Pollux. Pollux is the brightest star in Gemini,shining at magnitude 1.15. It is also the closest giant star to our Sun, located about 34 light-years away. Pollux’s radius is nine times larger than the Sun’s. To the right of Pollux, is the “head” of Pollux’s dimmer brother, Castor. Castor is a double-star shining at magnitude 1.90. As Venus is setting at 11:05 p.m., Jupiter can be found about 30 degrees above the southern horizon. Jupiter’s moon Io begins to transit across the planet at 22 minutes past midnight. At 1:02 a.m., Io’s shadow begins to follow its source. Io’s transit ends at 2:32 a.m., and its shadow transit ends 40 minutes later. Thursday night, two of Jupiter’s Galilean moons will be missing from your view. At 11:10 p.m., Jupiter’s largest moon, Ganymede, disappears behind the planet, joining Io. Io will reappear out of the gas giant’s shadow at 12:20 a..m., and Ganymede reappears 36 minutes later. Saturn rises at 21:55 p.m., in the ”steam” of the Teapot asterism in Sagittarius. That “steam” is the dense star cloud and dust of the Milky Way. Mars rises at 1 minute past midnight in Capricornus.Mars’ brightness increases from magnitude -1.2 to -2.1 during June. Mercury is hidden by the Sun as it reaches superior conjunction on Wednesday.
The Last Quarter Moon occurs at 2:32 p.m. Wednesday, but doesn’t rise until 1:59 a.m. in Aquarius. Features of this phase of the Moon include the Apennine Mountains, which curve from the terminator toward the crater Copernicus. The Apennine Mountains curve around one side of the lava plain known as the Mare Imbrium. It is theorized that this mare was formed by a collision with another celestial object, possibly an asteroid, about 3.8 million years ago. It is one of the larger craters in the solar system. Toward the center of the Moon, away from the Apennines, and alongside the terminator, are the craters Herschel, Ptolomaeus, Alphonsus, and Arzachel. On the pole opposite the Apennines is the large crater Clavius. With a diameter of 140 miles, Clavius is the second largest crater on the visible side of the Moon.