New Moon yields Dark Skies and an Annular Eclipse, plus Neptune at Opposition!

The Moon and Planets

The Moon begins this week as a slim old crescent in the pre-dawn eastern sky. As we approach Thursday morning’s New Moon, it becomes hidden in the dawn’s glare. This New Moon occurs with the Moon near the Ecliptic, causing an Annular Eclipse of the Sun visible across central Africa from Gabon to Madagascar. Annular eclipses occur when the Moon is farther from the Earth (appearing smaller) while the Sun is closer to the Earth (appearing larger), so that the Moon cannot fully cover the sun, leaving a ring of exposed sunlight around the Moon. The eclipse is partial for most of Africa and the Indian Ocean.

Above: The western sky at 8:45 pm on September 3, 2016. Star Walk 2 software simulation.

On Friday after sunset, the Moon reappears, as a young silver sliver just to the left of Jupiter, and then it waxes fuller as it climbs away from the Sun. On Friday, September 2, it sits about 5° (less than a palm’s width) to the lower right (west) of bright, white Venus. And on Saturday, it hops eastward to sit about the same distance to Venus’ upper left. As a bonus, Jupiter will sit to Venus’ lower right.

Venus and Jupiter are still situated in the low western sky after sunset. As soon as the sky begins to darken, look for the two bright objects less than a palm’s width above the horizon. On Sunday (today), brighter Venus is about a finger width to Jupiter’s upper left. Each subsequent night, they separate as Venus climbs and Jupiter falls. By week’s end, we’ve lost Jupiter until it becomes a morning object in mid-October.

Bright reddish Mars continues to move rapidly eastward, and it’s especially noticeable as it leaves Saturn and Antares behind! As darkness falls, Mars is less than 20° (two fist diameters) above the southern horizon. Dimmer, yellowish Saturn sits about 5° (five finger widths) to the upper right of Mars, but that increases to 7° by the weekend. The two planets set about 11:30 pm this week. The prominent red star Antares is the twinkling object to Mars’ lower right.

The southern evening sky at 9:30 pm, showing Mars and Saturn over Scorpius . Star Walk 2 software simulation.

The Solar System’s two ice giant planets, Uranus and Neptune, are in the eastern evening sky. Distant, dim Neptune reaches opposition on Friday — the day of the year when we are between the planet and the Sun. On that day, we are closest to it, and it rises as the Sun sets, making it an all-night target. Neptune won’t look particularly large at opposition because it is still nearly 30 astronomical units (the mean Earth-Sun separation) away. At that distance, its light takes four hours to reach our eyes! Uranus rises about 9:30 pm this week. Due to their extreme distance, they change location very little from week to week. I wrote about spotting them, and posted a sky chart, here.


Iridium flares are glints of sunlight off of the flat reflecting sides of one of the satellites that comprise the Iridium pager and sat-phone network. The flares occur before dawn and after dusk, when the satellite passing overhead is still illuminated by the Sun, which is below the horizon for observers on the ground. The duration and brightness depend on the angles between the observer, the satellite, and the Sun. For even more info about Iridium Flares and the space station, see an article that I wrote here. Using an accurate clock, go outside a few minutes ahead and look in the direction indicated. You should first see the dim Iridium satellite moving quickly across the sky, and then it will rapidly brighten for 3 to 8 seconds, and fade out. Truly spectacular! The more negative the Magnitude number, the brighter. The larger the Alt. number, the higher up it is! (The horizon is 0°, and 90° is straight up, so 55° is a bit higher than halfway between the horizon and zenith.)

Stargazing News for this week (from August 28th) by Chris Vaughan.

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