Skywatch Line for Monday and Tuesday, June 4th and 5th, 2018

This is the Skywatch Line for Monday and Tuesday, June 4th and 5th.

The Sun sets at 8:30 PM; night falls at 10:42. Dawn begins at 3:05 AM and ends with the Sun rising at 5:18.

The early evening sky contains only two bright planets. Venus, in Gemini, blazes with minus 4th magnitude and hangs 20º above the western horizon. It appears about 80% lit and sets at 11:08 PM. It is found 5º left of the star Pollux. Jupiter, in Libra, clings close to the bright star Alpha Librae, also called Zubenelgenubi, shines with minus 2nd magnitude and appears about 44 arc-seconds in size. Telescopic observers can see the moon Europa disappear behind the planet at 10:20 PM on Monday; it reappears at 1:48 AM, Tuesday. The Great Red Spot is visible at 12:03 AM on Wednesday. Jupiter is best observed at about 10:53 PM and sets at 3:57 AM.

Sagittarius houses two Solar System members. Saturn rises at about 10 PM and glows with 0.1 magnitude. By Midnight, it shines near the Teapot’s top, about 16º high and is best observed at 2:33 AM through binoculars or telescopes. The asteroid 4Vesta shines at 5.8 magnitude. It rises at 9:17 PM and is best observed at 2:10 AM about 6º northwest of Saturn. Although visible to the naked eye, Vesta is surrounded by similar looking stars. Detailed sky charts from magazines and astronomy websites are helpful in finding this brightest asteroid in the Solar System. Vesta is preparing for a June 19th opposition.

The Dawn sky is packed. We already mentioned Jupiter, Saturn and Vesta. Mars, in Capricornus, rises after Midnight, shines with minus 1st magnitude, appears about 90% illuminated and about 22º high. The Red Planet is becoming larger and brighter steadily and invites observation of its surface. Astronomy magazines provide Martian maps to assist sky watchers. It is highest at 4:39 AM. Neptune, in Aquarius, rises at 1:32 AM and glows with 8th magnitude near the star Phi Aquarii.

The waning Moon also occupies Aquarius on both nights. Tuesday, the 21-day-old Moon rises at 12:55 AM, blazes with minus 10th magnitude and appears about 64% lit. Wednesday, the Moon is a bit dimmer, about 55% phase and rises at 1:25 AM.

When you are done observing Jupiter, turn your attention to the star Porrima, in Virgo. The Latin name refers to a Goddess of Prophesy. The star lies midway between Spica, in Virgo, and Denebola, Leo’s tail. Porrima is a double star. Both stars are nearly identical. They are about the same brightness, third magnitude, and the same mass, about 1.5 times the Sun. They are sun-like, but significantly brighter and warmer. Like the Sun, Porrima and its companion are main sequence stars, fusing hydrogen into helium. Porrima was among the first double star systems discovered. Sir John Herschel calculated its orbit in 1833. They share a highly elliptical orbit and complete one cycle in about 169 years. An observer, with high power eyepieces in the telescope, can see them about 1.7 arc seconds apart.

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