Skywatch Line for Wednesday, August 9th, and Thursday, August 10th, 2017

This is the Dudley Observatory Skywatch Line for Wednesday, August 9th, and Thursday, August 10th, written by Louis Suarato

Wednesday’s sunset occurs at 8:05 p.m., followed by civil twilight, which ends at 8:35 p.m., when the center of the Sun is 6 degrees below the horizon. During this twilight phase, only the brightest stars and planets can be seen. Nautical twilight, when the Sun is 6 to 12 degrees below the horizon, ends at 9:13 p.m..This is when the horizon can still be seen along with the brightest stars, making it possible for celestial navigation. Astronomical twilight occurs between 9:13 and 9:55 p.m., when the Sun is 12 to 18 degrees below the horizon. Fainter objects begin to appear during this twilight phase.

Catch Jupiter over the west-northwestern horizon before it sets at 10:26 p.m. alongside Spica. Saturn is an easier target, at 25 degrees above the southern horizon. Moonrise occurs at 9:16 p.m. in the constellation Aquarius. The Moon is 94% illuminated, and at its waning gibbous phase as it rises. Use binoculars or a telescope to find Neptune 2 degrees to the upper right of the Moon Wednesday night. Venus rises, 77% illuminated, at 3 a.m. in Gemini.

On August 9, 1832, Henry Draper took the first photo of the spectrum of a star. It was in 1802, that William Wollaston discovered a star’s spectrum was comprised of boundaries separating its colors. Later discoveries determined that these spectral lines were comparable to those of earthly substances. These discoveries proved that Earth and stars contained many of the same materials. Draper, a pioneer of astrophotography, targeted Vega for his first spectral photograph. Vega is the brightest star in Lyra, second brightest in the northern hemisphere to Arcturus, and one of the stars in the Summer Triangle. Vega’s spectral class is categorized as AOV, indicating it is a blue-tinged white main sequence star that is fusing hydrogen to helium at its core. Vega’s current age is estimated to be 455 million years, about half of its expected life.

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