This Week’s Sky: September 1 – 8

The Moon steals the show as it waxes from first-quarter to full.

All Week

Evening sky Sept 4

The evening sky, mid-week, facing south-southwest one hour after sunset.

Mars and Saturn still rule the early evening sky, but neither is at its best. Both planets are less than 20-degrees high as twilight starts to fade, which doesn’t bode well for telescopic viewing. It’s interesting though to watch the space between the planets increase from night to night as Mars heads eastward. Each night they grow nearly a Moon’s diameter farther apart.

Meanwhile, Jupiter is taking over from Venus as the morning “star.” The big planet is climbing higher and higher and now stands nearly 10 degrees above the eastern horizon at the start of astronomical twilight. Venus, on the other hand, doesn’t rise until 5:30 a.m., local daylight time — about 1¼ hours ahead of the Sun. The brilliant planet will continue to be a fixture in the morning sky for many weeks yet.

September 2

At 7:11 a.m., EDT, the Moon is at first-quarter phase. That means by the time evening twilight begins, the lunar disc will already be a little more than half lit. At this time of year, the first-quarter Moon is also riding low on the ecliptic, so telescopic views will likely be compromised by mediocre seeing conditions.

September 5

Venus and Regulus

Venus and Regulus as seen in 10×50 binoculars a half hour before sunrise.

This morning Venus lies less than one degree from 1.4-magnitude Regulus, the brightest star in Leo. Unfortunately, this close encounter happens is brightening twilight, which means you’ll likely need binoculars (or a small telescope) and an unobstructed eastern horizon to see it.

September 8

Gary Seronik - Harvest Moon rising.

Last year’s Harvest Moon rises above Victoria, British Columbia, and the distant mountains of Washington State. Courtesy Gary Seronik

This is a big night. Not only will the Moon be full, but it is also the Harvest Moon and (as if all that wasn’t enough), it’s also a “super” Moon. How the hyperbole-prone popular press covers this lunar trifecta will likely be only slightly less interesting than the full Moon itself. The Moon is full at 9:38 p.m., EDT, having reached perigee (its closest to Earth) less than 22 hours earlier. According to a recent NASA press release, this is the third “super Moon” in a row. It’s also the Harvest Moon since it’s the full Moon nearest to the autumn equinox. Incidentally, the September full Moon edges out the October one for this designation by just 10 hours!

Weekend Stargazer

The bright crater Aristarchus is positioned near the terminator in this photo of a gibbous Moon. Courtesy Gary Seronik

The bright crater Aristarchus is positioned near the terminator in this photo of a gibbous Moon. Courtesy Gary Seronik

The September 5 – 7 weekend is full of moonlight, which means deep-sky observers will be taking a break from the action. Pickings are a bit slim for planetary observers too. The big three — Mars, Saturn and Jupiter — are too low for good telescopic views. Luckily, the Moon is always interesting and this weekend provides a good opportunity to enjoy Aristarchus — one of the most interesting craters on the lunar surface.


Aristarchus and its surroundings. Courtesy Gary Seronik

Aristarchus is an eye-catchingly bright 40-kilometre-wide impact crater situated on the Aristarchus Plateau — the surrounding diamond shaped area. Use 100× in your telescope and look closely at Aristarchus. You should be able to see the usual vertical banding on the interior crater wall. The region surrounding Aristarchus is full of interesting features as well, not least of which is the 160-km-long Schröter’s Valley, which was likely carved by flowing lavas long ago.

The Aristarchus region is not only visually fascinating, it’s also one of great historical interest. Perhaps no other region of the lunar surface has received as much attention from those hoping to see transient lunar phenomena (TLP), which would indicate ongoing volcanic activity. In spite of decades of effort, no convincing evidence for TLP has surfaced.

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