This is the Skywatch Line for Monday and Tuesday, June 10th and 11th, written by Joe Slomka.
The Sun sets at 8:33 PM; night falls at 10:48. Dawn breaks at 3:01 AM and ends with the Sun rising at 5:16.
Mars and Mercury share Gemini. Mars remains at 1.8 magnitude all month. It appears about 4 arc-seconds in size and about 13º high. Mars sets at 10:30 PM. Mercury is brighter, at magnitude minus 0.3, 64% illuminated but 9º high. Mercury sets at 10:12 PM. Note that Mars appears lower daily, while Mercury rises higher daily.
The Moon is at First Quarter on Monday night. In Virgo, the 8-day-old Moon appears about 59% lit and 32 arc-minutes in size, blazes with minus 10th magnitude, and is 47º high at Civil Dusk. Tuesday finds the Moon a bit fatter, brighter, but about the same size and 45º high. The Moon sets at 2:10 AM on Tuesday and at 2:38 AM, Wednesday.
Jupiter rises in the East, in Ophiuchus, at 8:19 PM. Monday, it reaches Opposition, which means it is up all night, at its brightest and at its closest to Earth in 5 years. It glimmers with minus 2nd magnitude, appears 46 arc-seconds in size but only 7º high. It is best observed at 12:52 AM. The giant planet, even at its highest, is so low that one rarely sees steady images in the telescope. Jupiter is retrograding (heading West) above Scorpius. Jupiter’s Great Red Spot, a giant storm, can be telescopically spotted at 3:07 AM on Wednesday. Also, on Wednesday the Moon Io begins to cross Jupiter’s face at 12:33 AM, followed by Io’s shadow at 12:36, followed by Ganymede exiting Jupiter at 1:40 AM and finally Ganymede’s shadow also exiting at 1:54 AM. This is its second double shadow transit in a week; a rare observing event. Jupiter sets at 5:25 AM.
Dwarf Planet 1Ceres also inhabits Ophiuchus, about 12º to Jupiter’s upper right. It shines with 7th magnitude but is a tiny 0.7 arc-seconds in size and 26º high. It rises at 7:09 PM and sets at 4:48 AM. Finder charts are available from magazines and online.
Saturn rises to the left of Sagittarius at 10:24 PM. It shines with zero magnitude, about 13º high at Midnight, and appears about a third of Jupiter’s size. Saturn is best observed at 3:00 AM.
Three planets appear in the pre-sunrise East. Neptune rises first in Aquarius at 1:15 AM, glowing with 8th magnitude, 2 arc-seconds in size and 18º high by Dawn. Uranus rises in Aries at 2:59 AM, shining with 6th magnitude and 3 arc-seconds, and 18º high. Venus brings up the rear by rising in Taurus. It appears about 95% lit, glistening with minus 4th magnitude and appearing 10 arc-seconds. However, it is only 3º high at Civil Dawn. All three pose a challenge for the sky-watcher, because of the rapidly brightening sky.
The dim constellation Virgo lies below Leo’s tail. Its brightest star, Spica, is not bothered by lunar glare. Virgo and Spica are ancient, known to all early civilizations, and studied for millennia. It is almost exactly first magnitude and one of the closest to Earth. In 1890, examination of Spica’s light revealed an unseen companion. A little-known space probe has changed our view of Spica. MOST, a satellite that studies variable stars, revealed that Spica is an eclipsing binary. In other words, two stars – one large and one smaller – eclipse each other every four days. The dimming is very slight. The brighter star itself varies. They are so close that they are egg-shaped, not oval. These discoveries reveal the main star’s diameter and set an upper limit on its size. At 260 light years away, Spica is an example of a star likely to go supernova – blow itself up – in the not too distant future.