Skywatch Line for Friday, June 8 through Sunday, June 10, 2018

This is Dudley Observatory’s Skywatch Line for Friday, June 8 through Sunday, June 10, written by Sam Salem.

On Friday, the Sun rises at 5:17am and sets at 8:33pm; the waning crescent Moon rises at 2:50am and sets at 3:42pm.

Venus, at magnitude –4.0, begins its slow descent sunward. It will remain the “evening star” until the end of September. On Friday evening at dusk, Venus and Pollux, the brightest star of constellation Gemini, are separated by a bit less than 5 degrees. Venus makes a line with the Gemini brightest stars, Castor and Pollux, to right of Venus in the next couple of evenings. Castor and Pollux are visible to the eye 75 to 90 minutes after sunset.

Jupiter, at magnitude –2.4, is a telescopic target when it reaches its highest around 11pm. Jupiter sets around 3:41 am on Friday. Saturn, at magnitude 0.1, rises in the south-southeast a little before 10pm. Saturn climbs to the meridian a little before 3am. Mars, at magnitude –1.4, is beginning to attract attention, in advance of its close approach at the end of July, as the planet’s disk is currently 16 arc seconds across. This is already larger than it appeared during four of the five most recent oppositions. Mars rises at little after midnight and culminates around 5am.

One of the season’s most interesting globular clusters is M4, in constellation Scorpius. The 5.6-magnitude cluster is positioned due south around 11pm. Look for a fuzzy object near red Antares, the brightest star in Scorpius. This is M4, one of the closest globular star clusters to Earth. M4 has a brief observing window because of its southerly declination. M4 is different from typical globulars. The Scorpius cluster appears loose and ragged. That’s partly because it’s one of the nearest globular clusters, lying only 7,200 light-years away.

Look in the northeast near the star Vega and try to find Rastaban and Eltanin stars in the constellation Draco, the Dragon. Rastaban and Eltanin are noticeable because they’re relatively bright and near each other. These two stars represent the fiery Dragon’s Eyes of the constellation Draco. Draco is Latin for dragon. Rastaban and Eltanin are derived from the Arabic language. Eltanin means “the dragon”. Rastaban means “head of the serpent”.

Friday marks the 393rd. birthday of the Italian-French astronomer Giovanni Domenico Cassini. In 1675, Cassini discovered the dark gap subdividing Saturn’s rings into two parts, now known as Cassini’s Division. He concluded that Saturn’s ring, believed by Huygens to be a single body, was composed of small particles. Cassini also discovered four of Saturn’s moons: Iapetus, Rhea, Tethys, and Dione. He observed shadows of four Galilean satellites on Jupiter, and measured its rotation period by studying the bands and spots on its surface. He determined the period of rotation of Mars, and attempted the same for Venus.
The Saturn orbiter, launched in 1997 as part of the Cassini-Huygens mission, was named after Giovanni Cassini. Its Titan probe was named Huygens in honor of the Dutch scientist, Christiaan Huygens, who discovered Titan in 1655.

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