Skywatch Line for Monday and Tuesday, May 14th and 15th, 2018

This is the Skywatch Line for Monday and Tuesday, May 14th and 15th.

The Sun sets at 8:10 PM; night falls at 10:09. Dawn breaks at 3:33 AM and ends with sunrise at 5:32.

The Moon turns “New” on Tuesday at 7:48 AM. It will be absent from Monday’s evening and Wednesday’s Civil Dawn.

Two bright planets adorn the evening sky. Venus blazes moderately low, about 20º, in the southwest at minus 4th magnitude and appears about 85% lit. Wednesday finds Venus closest to the Sun, what astronomers call perihelion. Venus is slowly climbing higher in our sky, until August. Venus sets at 10:45 PM.

Meanwhile, Jupiter also rises higher daily in the eastern sky. It is the brightest object in Libra, about 2º from the constellation’s brightest star, Zubenelgenubi, also called Alpha Librae. Gleaming at minus 2nd magnitude, Jupiter rises before sunset and stays up almost all night. It is best observed about 12:26 AM. Telescopic observers can see the Great Red Spot (a giant storm) on Tuesday at 2:19 AM and 10:10 PM. Also, on Tuesday, they can witness the Jovian moon IO begin to cross the planet’s face at 12:42 AM, followed by its shadow at 12:50; IO exits the planet at 2:50 AM, followed by the shadow at 3 AM. Jupiter sets shortly before sunrise.

Saturn rises at 11:22 PM in Sagittarius. By midnight, the zero-magnitude planet is about 5º high. The asteroid 4Vesta also shares Sagittarius. The 6th magnitude rock is about 10º high, but a tiny half-arc-second in size. Detailed charts are necessary to find this challenge object. Both Saturn and 4Vesta are near the top of the “Teapot” asterism, surrounded by binocular visible star clusters. Both objects are highest in the sky about 4 AM.

Mars, in Capricornus, shines at minus 1st magnitude, appearing about 89% illuminated and about 20º high. As previously mentioned, Mars continues to brighten and grow larger in our instruments until Opposition in July. Having risen at 12:57 AM, it is best observed at about 3:30 AM. At that time, the observer sees it very close to M75, a globular star cluster.

Neptune rises at 2:54 AM in Aquarius and is highest in pre-dawn skies. It glows with 8th magnitude and is 2 arc-second blue-green dot, requiring sky charts for location.

With Venus so prominent in southwest, let us examine her in detail. Venus is the second planet from the Sun. It is almost an Earth twin, about the same size and slightly less mass. Early telescopic observers noted its complete cloud cover. They speculated that Venus was a lush, tropical planet. As science obtained better instruments, rude shocks came. Venus did not rotate in 24 hours like Earth; its day lasts 243 earth-days. Russian and US probes landed on Venus; pictures showed a rock filled wasteland. Those same probes recorded a toxic atmosphere with true acid rain. Since Venus is closer to the Sun, it gets twice the solar radiation. Temperatures approach the melting point of lead and atmospheric pressure is 90 times that of Earth. Its slow rotation and lack of axis tilt means no seasons or weather. Most planetary scientists now think that Venus is a case of uncontrolled global warming. Any oceans boiled off, leaving an atmosphere of 96 percent carbon dioxide. Without oceans, there was no water to capture carbon dioxide into limestone rocks, as on Earth.

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