This is the Skywatch Line for Monday and Tuesday, September 9th and 10th.
The Sun sets at 7:16 PM; night falls at 8:54. Dawn begins at 4:51 AM and ends with the Sun rising at 6:29.
The Moon joins Jupiter and Saturn as the bright attractions in tonight’s sky. On both nights 11-day-old Moon blazes in dim Capricornus with minus 11th magnitude. Monday sees it as 85% illuminated and 18º high in the South; it is best observed at 9:59 PM. Tuesday, the Moon is fatter, slightly brighter and is highest at 11:47 PM. The Moon sets at 2:47 AM on Tuesday and at 3:45 AM on Wednesday.
Jupiter, in Ophiuchus, shines with minus 2nd magnitude and is about 23º high in the southwest. The giant gas planet, nearing the end of its appearance, presents few opportunities to see events on its face; the Great Red Spot, a giant storm, is centered at 9:52 PM on Monday. It sets at 11:12 PM.
Saturn, in Sagittarius, also glows in the southern sky, but at zero magnitude and appears about 1/3 Jupiter’s size. It, too, is about 23º high and its famous rings are best enjoyed at 8:41 PM. Saturn sets at 1:13 PM.
Dwarf Planet 1Ceres still occupies Scorpius by appearing about 3º above the red star Antares. It is fading to 9th magnitude and lies about 13º above the horizon. It sets at 10:38 PM.
Neptune rises in Aquarius at 7:14 PM. It glows with 8th magnitude and appears about 2 arc-seconds in size. It is best observed at 12:54 AM, when it is about 25º high. Tuesday, at 4:00 AM, the planet reaches Opposition, when it is aligned with the Earth and Sun; it also rises at sunset and sets at sunrise. This is the best time all year to find it and observe this most distant planet of our Solar System.
Uranus rises in Aries at about 9:00 PM. It glows with 5th magnitude and is about 3 arc-seconds in size. It is located about 31 degrees high. Its blue-green tint helps finding it. It is highest at 3:55 AM. Finder charts for 1Ceres, Neptune and Uranus are available from astronomy magazines and websites.
The constellation Perseus is well up after Midnight. At 11:47 PM on Monday, the star Algol (also known as B Persei) dims. Algol, the “Demon Star,” varies its light every 2 days, 20 hours and 49 minutes. It fades from second magnitude to third – easily seen by the naked eye. The entire cycle takes about nine hours. Two hundred and thirty years ago, John Goodricke theorized that a dimmer star was partially eclipsing a brighter star. In 1889, the new technique of spectroscopy verified this theory. The main star is one hundred times the Sun’s luminosity. The eclipsing star is actually slightly brighter than our Sun. There is a third star that orbits the system once every 1.8 years, but plays little part in the occultation. The system is about 96 light years away and the most easily studied “eclipsing binary.” Astronomy magazines and websites provide timetables of its eclipses.