This is Dudley Observatory’s Skywatch Line for Friday, October 18, through Sunday, October 20, written by Sam Salem.
On Friday, Sun rises at 7:12am and sets at 6:09pm; the waning gibbous Moon rises at 9:18pm and sets at 11:48am.
Saturn, at magnitude 0.5, resides among the background stars of constellation Sagittarius the Archer, 25 degrees high in the south-southwest as twilight fades to darkness. It appears significantly brighter than any of its host constellation’s stars. Even a small telescope shows Saturn’s disk and spectacular ring system, which spans 37 arc-seconds and tilts 25 degrees to our line of sight. Saturn sets around 11pm.
Mercury reaches greatest elongation at midnight on Saturday. At that time, Mercury stands 25 degrees east of the Sun. Mercury climbs just 3 degrees high 30 minutes after sunset. Mercury and Venus are very low in bright twilight after sunset. Start by trying for Venus, at magnitude –3.9, just above the west-southwest horizon a mere 20 minutes after sunset. Some 8 degrees to its left is Mercury, much dimmer at magnitude –0.1. That’s only 3 % as bright as Venus. Use binoculars to help you locate Mercury.
Jupiter, at magnitude –2.0, is the white dot low in the southwest in the feet of Constellation Ophiuchus, as twilight fades. Jupiter is nearly on the far side of the Sun from us, appearing only 35 arc-seconds wide in a telescope and very smush in the low-altitude seeing.
Vega, in constellation Lyra, is the brightest star high in the west after dark. To its lower right by nearly a fist and a half at arm’s length, look for Eltanin, the nose of Draco the Dragon. The rest of Draco’s fainter, lozenge-shaped head is a little farther behind. Draco always eyes Vega. The main stars of Vega’s own constellation, Lyra, now extend to Vega’s left. They are quite faint by comparison. Altair, in constellation Aquila, is about equally high as Vega but not quite as bright. Just upper right of Altair, by a finger-width at arm’s length, spot little orange Tarazed. Down from Tarazed runs the stick-figure backbone of Aquila, the Eagle. If you have a dark sky, make your acquaintance with the constellation Draco. Draco is a circumpolar constellation. It is out all night long every night of the year. This serpentine star figure wanders in between the Big and Little Dippers, with its tail found between the bowl of the Big Dipper and the star Polaris.
Friday marks the 30th. anniversary of Galileo space orbiter launch. The craft gained speed from gravity assists in encounters with Venus and Earth before heading outward to Jupiter. During its six year journey to Jupiter, Galileo’s instruments made interplanetary studies, using its dust detector, magnetometer, and various plasma and particles detectors. It also made close-up studies of two asteroids, Gaspra and Ida in the asteroid belt. The Galileo orbiter’s primary mission was to study Jupiter, its satellites, and its magnetosphere for two years.