Skywatch Line for Friday, October 5 through Sunday, October 7, 2018

This is Dudley Observatory’s Skywatch Line for Friday, October 5 through Sunday, October 7, written by Sam Salem.

On Friday, the Sun rises at 6:57am and sets at 6:30pm; the waning crescent Moon rises at 2:30am and sets at 4:56pm. The new Moon occurs on Monday at 11:47pm.

Jupiter’s current apparition is nearly over. It hovers at magnitude –1.8, less than ten degrees above the southwest horizon 45 minutes after sunset. Saturn, shining at magnitude 0.5, is positioned a little west of the meridian. Mars glows at magnitude –1.2 from western constellation Capricornus. The Martian disk is considerably smaller than it was at its peak this summer. It has shrunk from 24.3 arc-seconds down to its current diameter of 15.3 arc-seconds.

Venus is heading directly into the Sun’s glare. During the first week of October Venus becomes lost from view from mid-Northern latitudes. Venus reaches its stationary point in Southwestern constellation Libra this Friday. The planet then commences retrograde, East to West motion, turning back towards constellation Virgo and re-entering that constellation at its extreme Southeastern corner on Monday.

This moonless weekend is an opportunity to spot Uranus with your naked eyes. Uranus, at magnitude 5.7, sits near the Aries-Pisces constellations border. It is easy to find with binoculars if you have a finder chart and know the constellations well enough. Uranus rises around 7:09pm on Friday, reaching transit altitude of 59 degrees south at 1:58am.

The constellations of summer and fall lie within reach before midnight. One summer object currently in prime position at nightfall is the Ring Nebula M57 in constellation Lyra. The Ring nebula is relatively bright, glowing at magnitude 8.8. However, the nebula spans only 70 arc-seconds, which is slightly less than twice the apparent size of Jupiter. Fortunately, M57’s location is easy to find. It is situated between the stars Lambda (λ) and Beta (β) Lyrae, a little closer to Beta than Lambda. Small telescopes used at low magnification will show the tiny, ghostly disk. With higher power you will be able to see the dark central hole that gives the Ring its name.

Spot Vega with your naked eyes before sunset this weekend. Vega reaches transit altitude of 86 degrees south, a few minutes after sunset, around 6:35pm on Friday. Vega is the brightest star very high in the west right after nightfall. Arcturus, equally bright, is getting low in the west-northwest. The brightest star in the vast expanse between them, about a third of the way from Arcturus up toward Vega, is Alphecca, at magnitude 2.2. Alphecca, the crown jewel of Corona Borealis, is a 17-day eclipsing binary. However, its brightness dips are too slight for the eye to see.

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