Skywatch Line for Wednesday, July 21 and Thursday, July 22, 2021

This is Dudley Observatory’s Skywatch Line for Wednesday, July 21 and Thursday, July 22, written by Alan French.

The Sun now sets at 8:34 p.m. and rises at 5:35 a.m. The days are slowly growing shorter.

A waxing gibbous Moon now brightens the night sky. A 94% illuminated Moon will rise at 6:49 P.M. Wednesday. It will be 98% in sunlight when it rises at 7:54 Thursday, appearing essentially full. The Moon will reach full Friday night.

There have been many reports of a reddish Moon and Sun due to smoke from the western forest fires. A friend in Pennsylvania, where the skies were clear of clouds Tuesday night, reported that only the Moon and Vega were visible in his smoke polluted night sky. Our recent rains may have cleared some of the smoke, but watch the Moon rise for signs of smoke over our region. If the heavy smoke persists or is renewed, some coloration may be visible when the Moon is high in the sky.

If you look high in the east, almost overhead, at 10:00 P.M. you’ll find bright Vega, the fifth brightest star in the night sky and the brightest star in the small constellation, Lyra, the Lyre. Like many bright stars, Vega is bright because it is a close neighbor, lying just over 25 light years away from us. Its light, traveling at 300,000 kilometers per second (186,000 miles per second) took over 25 years to reach your eyes, so it left star in early 1996.

Vega was the first star, other than our Sun, to be photographed, having its celestial portrait taken on the night of July 16-17 in 1850. The photo was a daguerreotype, a process which creates a detailed image on a sheet of copper coated with silver. The photo was taken through the 38-centimeter (15-inch) aperture refractor at the Harvard Observatory by William Bond and James Adams Whipple.

Installed in 1847 the 38-centimeter refractor at Harvard was the largest telescope in the United States for 20 years, and was known as “The Great Refractor.”

Vega was also the first star, other than our Sun, to have its spectrum photographed, by Henry Draper in August, 1872. Like the spectrum of the Sun, the star’s spectrum showed absorption lines, dark lines where specific wavelengths or colors emitted by the star were absorbed by cooler gases in upper layers of its atmosphere.

The constellation Lyra is easily spotted, made up of a small parallelogram of four equally bright stars to the southeast of Vega and a single star of similar brightness to the northeast. A lovely planetary nebula, the Ring Nebula, lies directly between the closer spaced pair of stars in the parallelogram farthest from Vega. Being close to obvious landmarks, the Ring Nebula is a fine, easily located, target for beginning telescope users

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