Skywatch Line for Friday, December 28 through Sunday, December 30, 2018

This is Dudley Observatory’s Skywatch Line for Friday, December 28 through Sunday, December 30, written by Sam Salem.

On Friday, the Sun rises at 7:26am and sets at 4:29pm; the waning gibbous Moon rises at 11:42pm and sets at 11:45am. The Moon reaches last-quarter phase on Saturday at 4:34am. Watch the Moon in the vicinity of Spica, the constellation Virgo’s one and only 1st-magnitude star, on Saturday and Sunday.

Mars, at magnitude 0.4, is the sole planet residing in the evening sky. Mars continues its eastward travel, prolonging its descent into twilight. Mars will linger at dusk until spring transitions to summer. Venus, the “morning star”, is gleaming at magnitude –4.7. It rises around 3:35am and climbs to an altitude of nearly 20 degrees before the first hint of morning twilight. Next to rise is magnitude –1.8 Jupiter. It clears the southeast horizon around 5:30am. Jupiter doesn’t get high enough for viewing in a scope just yet. Mercury, at magnitude –0.4, rises around 6:05am. The innermost planet is nearing the end of its most favorable appearance for this year. On Monday morning, step outside to enjoy a special view in the east before sunrise. The Moon, Venus, Jupiter, and Mercury are arrayed in a tidy line angled above the southeast horizon. In their order from top to bottom, you’ll see the waning crescent Moon, Venus, Jupiter, and Mercury. That also happens to be their order in brightness. The best time to take in the scene is roughly 45 minutes before sunrise. Mercury is the faintest of these worlds and the lowest in the sky. It’ll be the toughest to spot. To catch it, you’ll need an unobstructed view to the southeast. Look for Mercury close to the horizon, along line with the Moon, Venus and Jupiter, with the unaided eye or binoculars.

Evenings over this weekend are free of moonlight, giving a change to enjoy some of the late autumn’s deep-sky objects, including M33. Although catalogued as a magnitude 5.7 object, the spiral galaxy M33, in constellation Triangulum, can be difficult to observe in a light-polluted sky. The galaxy is both large, more than one degree across, and nearly face-on. Its light is spread out across a substantial area. In a telescope, M33 can be seen as a pale cloud. Its surface brightness is so low that the galaxy simply blends in with the background sky glow. In ideal conditions, far from town, M33 can be glimpsed with the naked eye, but from the suburbs it’s often hard to detect even in a good-sized telescope. M33 is one of the few galaxies that have their own built-in deep-sky objects. The most attracting of these is a knot of nebulosity lying northeast of the galaxy’s central hub. Listed as NGC604, this little blob can be spotted with a 4-inch scope in less-than-pristine skies. You will need to boost the magnification well beyond what you would use to view M33.

Sir Arthur Stanley Eddington, the English astrophysicist and mathematician, was born on December 28, 1882. He is known for his work on the motion, distribution, evolution and structure of stars. In 1917, he was one of the first to suggest, conversion of matter into radiation powered the stars. Sir Eddington interpreted Einstein’s general theory of relativity, and in 1919 he led a solar eclipse expedition, which confirmed the predicted bending of starlight by gravity. He developed an equation for radiation pressure. In 1924, he derived an important mass-luminosity relation. He also studied pulsations in Cepheid variables, and the very high densities of white dwarfs.

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