Skywatch Line for Friday, January 9, through Sunday, January 11, written by Sam Salem
This is Dudley Observatory’s Skywatch Line for Friday, January 9, through Sunday, January 11, written by Sam Salem.
On Friday, Sun rises at 7:25am and sets at 4:40pm; Moon sets at 10:44am and rises a 11:59pm.
The last quarter Moon occurs on Saturday at 10:48am. Look for the “terminator”, the moving line separating the sunlit side from the dark side, when Moon rises around 1 am Saturday night (Sunday morning) as it looks slightly concave. Springtime star Spica, the brightest star in Virgo the Maiden, shines above the Moon when it rises, by three or four finger-widths at arm’s length. By dawn the Moon will be high in the south with Spica to its upper right.
On Friday, Mars is in conjunction with the Sun at 7am. making the planet invisible from Earth. We’ll have to wait until mid-March to see it again, when it will shine in the predawn sky.
On Saturday night, Jupiter is at opposition, opposite the Sun as seen from Earth. It rises at sunset in the constellation of Gemini near Pollux and Castor all night. Jupiter, magnitude –2.7, rises in the east-northeast around sunset, dominating the eastern sky in early evening, then the high southeast. Jupiter is highest in the south around midnight Now It’s a big 47 arcseconds wide.
Saturn, magnitude +1.2 at the Aquarius-Pisces border, is the brightest object high in the southwest at nightfall. It sits lower left of the Great Square of Pegasus. In a telescope Saturn’s rings are still very thin but starting to open up. They’re now tilted a full 1° to our line of sight. The rings’ thin black shadow on Saturn’s globe is slowly becoming a little wider too.
Find the Keystone of Hercules in the eastern sky, about 40° high two hours before sunrise. Look for Vega, the alpha star of Lyra the Lyre, some 20° high at that time. Then, glance to the upper right for a rough square of the four Keystone stars located about ⅓ of the way from Vega to Arcturus in Boötes the Herdsman. The brightest Keystone star is magnitude 2.8 Zeta (ζ) Herculis, which is the star farthest right as the constellation rises, at the upper righthand corner of the Keystone. To its upper right in the sky is Eta Her, about 7° to Zeta’s north and forming the upper lefthand corner of the Keystone in this configuration. Use a telescope to glance about ⅓ of the way along a line from Eta to Zeta Her to find the Hercules Cluster (M13), a magnificent globular cluster glowing at 6th magnitude.
On January 11, 1787, Sir William Herschel discovered the first two moons of Uranus, Titania and Oberon. This was just six years after Herschel discovered Uranus. Titania the largest and Oberon the second largest moon, both named for characters from Shakespeare’s A Midsummer Night’s Dream. Herschel initially called them “number one” and “number two,”. They were later named by his son, John, following the literary tradition for Uranian moons.