This Week’s Sky at a Glance, September 9 – 17

Moon over Mars Sept. 9, 2016

The first-quarter Moon shines over Mars on Friday September 9th, with Saturn, Antares, and the Cat's Eyes looking on.

Mars, Saturn and Antares mid-September 2016

Fast Mars continues to pull farther away from Saturn and Antares in its background.

Friday, September 9

• First-quarter Moon (exact at 7:49 a.m. EDT). This evening the Moon, no longer exactly first-quarter, shines over Mars, as shown at right.

• The triangle of Mars, Saturn, and Antares, emblem of all this summer's evenings, continues to lengthen as summer nears its end, as shown in the two panels here. In the coming days and weeks Saturn and Antares will continue to move farther toward the lower right, while Mars hangs back and fades. By mid-autumn Saturn and Antares will be gone.

Saturday, September 10

• This evening the Moon shines over the Sagittarius Teapot. The Teapot, about the size of your fist at arm's length, is tipping and pouring to the right.

Sunday, September 11

• The Moon is just about equidistant from Altair, which is high to its upper left after dark, and Mars, which is far off to the Moon's right and somewhat lower.

Monday, September 12

• Now the Moon shines straight under Altair at dusk. A finger-width above Altair is Tarazed, Gamma Aquilae. Altair is 16.7 light-years distant; Tarazed is about 390. The name "Tarazed" comes for the Persian for "balance beam," referring to the pattern it makes with Altair and fainter Beta Aquilae on Altair's other side.

Tuesday, September 13

• As dusk turns to night, Arcturus twinkles due west. It's getting lower every week. And off to its right in the northwest, the Big Dipper is turning more and more level.

Wednesday, September 14

• How soon after sunset can you see the big Summer Triangle? Face east. Vega, the Triangle's brightest star, is practically at the zenith (for skywatchers at mid-northern latitudes). Deneb is the first bright star you encounter to Vega's east-northeast. Altair shines less high in the southeast.

Thursday, September 15

A winter preview: Step out before the first light of dawn this week, and the sky displays the same starry panorama as it will at dusk next February. Orion stands high in the south, Sirius and Canis Major sparkle to its lower left, and Gemini occupies the high east.

Friday, September 16

• Full Moon (exact at 3:05 p.m. Eastern Daylight Time). As night comes on, look for the Great Square of Pegasus to its upper left. The Square, a bit larger than a fist at arm's length, stands on one corner.

• A fairly deep penumbral (fringe) eclipse of the Moon is visible from eastern Europe, eastern Africa, Asia, and the westernmost Pacific. Map and full details.

Saturday, September 17

• Now the Moon shines below the Great Square of Pegasus. From the Great Square's left corner extends a big line of three 2nd-magnitude stars, running to the lower left, that mark the head, backbone and leg of the constellation Andromeda. The line of three includes the Square's corner.

Upper left from the end of this line, you'll find W-shaped Cassiopeia tilting up.

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Want to become a better astronomer? Learn your way around the constellations! They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Pocket Sky Atlas, jumbo edition

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the new Jumbo Edition for easier reading in the night. Click image for larger view.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or new Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5, nearly three times as many. The next up, once you know your way around, is the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."


This Week's Planet Roundup

Mercury and Jupiter are hidden in the glare of the Sun.

Venus (magnitude –3.8) is very low in the west in bright twilight. Look for it 20 or 30 minutes after sunset from a spot with a good open western view.

Mars (magnitude –0.1) continues moving eastward away from Saturn (magnitude +0.5) and Antares (+1.0, below Saturn) in the south-southwest at nightfall. The triangle they make is lengthening. Mars is now at the eastern foot of Ophiuchus; Saturn is at his western foot.

In a telescope, Mars is down to 10 arcseconds in diameter — about two thirds the size of Saturn's globe, but much more brightly sunlit.

Uranus (magnitude 5.8, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are well up by 11 or midnight in the southeast and south, respectively. Info and finder charts.

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All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.

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"This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours."
— Neil deGrasse Tyson


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