This is the Skywatch Line for Monday and Tuesday, April 18th and 19th.
The Sun sets at 7:41 PM; night falls at 9:26. Dawn breaks at 4:22 AM and ends with sunrise at 6:06.
The twelve-day-old Moon blazes at minus 11 Monday night and is best observed at 10:50. Tuesday night finds a brighter and fuller Moon highest at 11:32. It occupies Virgo both nights and sets after 5 AM both days.
Jupiter is also already up. It is located under Leo’s belly and is best seen at about 10 PM. While binocular watchers can see Jupiter and some of its four Galilean moons. Telescope users can witness events on Jupiter. Wednesday at 12:16 AM, one can see the Great Red Spot, a giant storm, on Jupiter’s face. Telescopes also reveal the moon Callisto begin its march across Jupiter at 8:38 PM Tuesday and exit the planet’s surface at 11:37 PM. Jupiter sets after 4:30 AM.
Mercury makes the best appearance of the year on Monday. It appears about 19 degrees above the western horizon. It shines is about 0.2 magnitude and, in telescopes, appears about 8 arc seconds in size. Mercury is at greatest elongation tonight, about twenty degrees east of the Moon. Use binoculars to spot it amid the sunset sky. Mercury sets about 9:30 PM.
Mars rises in Ophiuchus at 10:51 PM. The Red Planet steadily grows brighter and larger in our telescopes in preparation for its May opposition. Saturn, also in Ophiuchus, rises about a half-hour after Mars. Mars shines at minus 1.1 magnitude, while Saturn is a sedate zero magnitude. Both are best observed at about 4 AM. Saturn, Mars and the bright star Antares form a neat triangle Tuesday morning. Mars is the triangle’s apex, with Saturn seven degrees to Mars’ East and Antares about five degrees below Mars. All three are great sights in any size telescope. Saturn is famous for its rings, Mars for its red color, and Antares for its rival color to Mars. All three remain up the rest of the night.
Besides the rings, Saturn has sixty-two moons. One of these, Iapetus, has puzzled observers for centuries. Iapetus is bright when it is on one side of Saturn, but markedly darker when on the other.
Two groups of astronomers think they have figured it out. Iapetus is tidally locked to Saturn, just like the Earth’s Moon – showing the same side to the planet. The leading side of Iapetus sweeps up debris from a newly discovered (and invisible to amateurs) ring. Thus one side looks like it was covered in chocolate dust, while the trailing side is as white as snow, really ice. In addition, the dust, warmed by sunlight, melts the ice below, which flows to the trailing side and re-freezes. Iapetus has a 79.3-day orbit, and is visible in amateur telescopes. Astronomy programs and websites assist the observer.
The Albany Area Amateur Astronomers hold their monthly meeting at miSci on Thursday, April 21st at 7:30 PM. This month, club member David Scott talks about the Analemma, that strange figure-eight you see on maps and globes. He will explain it and how it helps astronomers. All club events are free and open to the public.