This is Dudley Observatory’s Skywatch Line for Friday, October 4, through Sunday, October 6, written by Sam Salem.
On Friday, Sun rises at 6:56am and sets at 6:32pm; the waxing crescent Moon rises at 1:33pm and sets at 10:51pm. The waxing Moon shines between Jupiter and Saturn on Friday. The waxing crescent Moon, Jupiter, Saturn, and Antares follow a gentle arc about 35 degrees long in the southwestern sky after sunset.
On Saturday, first-quarter Moon occurs at 12:47pm. The first-quarter Moon shines with Saturn, only about 2 degrees to its right or upper right at dusk in eastern Sagittarius, near the handle of the “Teapot”. Saturn is 3,800 times farther away than the Moon. In a telescope, Saturn’s largest satellite, Titan, at magnitude 8.7, looks like an orange pinpoint, four ring-lengths to Saturn’s east.
Saturday is the International “Observe the Moon” Night. It is an annual worldwide public event that encourages observation and appreciation of the Moon. Dudley Observatory has stargazing, Moon observing, and other hands on activities that night. Check the “Dudley Observatory at miSci” website for details. This weekend is a good opportunity to explore the Moon. Try to locate two of the main features observed around this time of first-quarter Moon. On Saturday, Locate Lunar X near crater Werner. The Lunar X is a clair-obscur, a strong contrast between light and dark, effect in which light and shadow creates the appearance of a letter ‘X’ on the rim of the Blanchinus, LaCaille, and Purbach craters. The X is visible only for a few hours before the first quarter, slightly below the lunar terminator, the line dividing light and shadow on the Moon. The Lunar X can be seen around 11pm on Saturday.
On Sunday evening, try to locate the Lunar Straight Wall, or Rupes Recta, Latin for straight cliff. First look for the trio of large craters right in the center of the terminator’s surface, Ptolemaeus, Alphonsus, and Arzachel. Just to the southwest of Arzachel is a large ruined crater, flooded by lava from the Mare Nubium. The Straight Wall is a huge fault crossing this crater. When the Sun illuminates the feature at an oblique angle at about day 8 of the Moon’s orbit, the Rupes Recta casts a wide shadow that gives it the appearance of a steep cliff.
Get good views of Uranus during the late evening hours this weekend. The ice giant planet rises during twilight, and it climbs nearly halfway to the zenith in the east-southeast by 11pm. It reaches its peak some 60 degrees above the southern horizon around 2am. Uranus glows at magnitude 5.7 against the backdrop of southern constellation Aries the Ram. Use binoculars to find the planet 2.5 degrees due south of the similarly bright star 19 Arietis. A telescope reveals Uranus’ blue-green disk, which spans 3.7 arc-seconds.
Friday marks the anniversary of Sputnik satellite launch. The Space Age began on October 4 1957, as the Soviet Union launched Sputnik, the first manmade satellite, into orbit around the earth. The spacecraft circled the earth every 96 minutes at almost 18,000 miles per hour, 500 miles above the Earth. Sputnik stayed in orbit for about three months. The 184 pounds satellite had transmitted radio signal picked up around the world. Sputnik was 6 times the size of the first U.S. satellite, which was scheduled to be launched the next year. The first U.S. satellite, Explorer, was launched on January 31, 1958.