Skywatch Line for Monday and Tuesday, June 13th and 14th, 2016

This is the Skywatch Line for Monday and Tuesday, June 13th and 14th.

The Sun sets at 8:35 PM; night falls at 10:51. Dawn begins at 3 AM and ends with the Sun rising at 5:16.

The nine-day-old Moon, just past First Quarter, is well up in the southern sky. Shining at magnitude minus 10.3, it occupies Virgo on both nights. Monday it lies the near the star Porrima; Tuesday night finds it five degrees above the bright star Spica, the constellation’s brightest star. The Moon sets after 2 AM on both nights.

Jupiter, well west of the Moon, still blazes at magnitude minus 2 between Leo’s hind legs. Jupiter’s stay in our sky becomes shorter daily; it sets now at 1 AM. Telescopic observers can witness the moon Io beginning to cross Jupiter’s face at 9:56 PM Tuesday, followed by its shadow at 11:10 PM.

The darkening sky reveals Mars, in Libra. It is still pulling away from Saturn, now 18 degrees away. The Red Planet is shrinking and dimming slightly after its opposition last month. However, it is still worthy of extended observation. Mars sets about 3:30 AM.

Saturn, in dim Ophiuchus, rises an hour after Mars and forms the second leg of the heavenly triangle with Mars and the star Antares. Saturn is 16 degrees away from Antares, which lies 15 degrees below Mars. The triangle keeps expanding with Mars’ westward motions. Saturn is always a great view in any size telescope because of its famed ring system. However, it has fleet of 62 moons, eight of which are visible through amateur telescopes. Astronomy magazines, websites and apps provide charts to identify those moons. Saturn sets about 4:50 AM.

Dawn finds Neptune, which rises at 12:44 AM in Aquarius, shining at 7.9 magnitude and having a size of 2.3 arc-seconds. It appears as a tiny blue-green dot amid the myriad stars. Uranus rises in Pisces, sparkles at magnitude 5.9 and appears 3.4 arc-seconds in our telescope eyepieces. The observer should work quickly to find them before the Dawn sky glow washes them out.

Mercury rises in Taurus at 4:11 AM. Even though it is at its highest this week, it is still only 5 degrees high by Civil Dawn. Again, Mercury is a challenge object.

When you are done observing the Moon, turn your attention to the close star Porrima. 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, which make 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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