Skywatch Line for Wednesday, September 11th, and Thursday, September 12th, 2019

This is the Dudley Observatory Skywatch Line for Wednesday, September 11th, and Thursday, September 12th, written by Louis Suarato.

The 95% illuminated, waxing gibbous Moon rises at 6:28 p.m., Wednesday. This month’s Full Moon occurs Thursday night at 33 minutes past midnight. It will be the Full Moon closest to the Autumnal Equinox and therefore is known as the Harvest Moon. At the time of the Harvest Moon, moonrise occurs early in the evening, and remains low on the horizon for several nights. The additional light from the Full Moon provides farmers with additional time to harvest their crops. Many think the Harvest Moon appears larger than all other Full Moons. The Harvest Moon’s size is a factor of its distance from Earth, just like all other Full Moons. This month’s Harvest Moon is only 9 hours away from lunar apogee, the furthest distance from Earth during this lunar cycle, 252,511 miles, so this Full Moon will appear about 15% smaller. Look for the nearly Full Moon to rise at 6:58 p.m. Thursday.

Astronomical twilight occurs at 8 p.m. providing about 10 hours of observable dark skies. Jupiter and Saturn remain the only easily visible planets in the night sky. Jupiter sets at 11:05 p.m. Wednesday, and Saturn sets at 1:01 a.m., Thursday. The two gas giants will continue to move closer until December when both will be lost in the glow of evening sunset. The gas giants, also known as the Jovian or outer planets, are those planets with masses 10 times greater than that of Earth. These planets, Jupiter Saturn, Uranus, and Neptune are made up mostly of hydrogen. Jupiter’s and Saturn’s cores are thought to be composed of a rocky core surrounded by of liquid hydrogen and helium.

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