September 12, 2018: Venus, Jupiter and the crescent Moon.
The sky is very clear this evening. The crescent moon, overexposed in the image, shows Earthshine. Sunlight reflected from Earth falls on the night portion of the moon and gently illuminates it. Brilliant Venus is just above the southwest horizon. In about 10 days, Venus begins its cycle of greatest brightness. Jupiter appears over 17 degrees to the upper left of Venus. Jupiter gets closer to Venus during the month, but there is no conjunction.
September 8: Before sunrise, locate the thin waning crescent moon (28.0 d, 2%) 1.8° to the upper left of Regulus with Mercury 4.4° below the star. Mercury (m = −1.2) is only 4.5° up in the east-northeast 30 minutes before sunrise. You’ll need a clear horizon and binoculars to see the trio in bright twilight.
September 6: In the predawn eastern sky, the waning crescent moon (26.0 d, 15%) is on a virtual line that connects the Gemini Twins, Castor (α Gem, m = 1.6) and Pollux (β Gem, m = 1.2). The moon is 9.2° from Pollux. Thirty minutes before sunrise, with binoculars, look in the east-northeast for Mercury (m = −1.1) 1.2° to the left of Regulus. Mercury is 6.5° up in the sky.
In the evening sky, Saturn’s retrograde ends. It is 5° to the upper right of Kaus Borealis (λ Sag, m = 2.8), the star at the top of the lid of the Teapot of Sagittarius, and 45° from Jupiter. Mars and Jupiter have the same visual brightness (m = −1.9). Because they have distinctly different colors, do they appear to be the same brightness to you? While they are over 70° apart, it is not appropriate in formal astronomy to compare respective objects’ brightness, but it is a fun activity. Look near the end of twilight because they have nearly the same altitude early in the evening.
September 1: Mercury (m = −9) is 10° up in the east-northeast, 30 minutes before sunrise. It is approaching a conjunction with Regulus (α Leo, m = 1.3). This morning Regulus is 7.8° below Mercury, and very difficult to locate, even with optical assistance and a perfect horizon.
In the evening sky, for most of the month, Venus (m = −4.7) and Spica (m = 1.0) set at nearly the same time, 85 minutes after sunset this evening. As they separate, Venus moves farther south. (Recall that the farther north an object the longer it stays in the sky.) As they slide into twilight the largest time gap in their setting times is 15 minutes. Jupiter (m = −1.9) is 24° to the upper left of Venus. (If the Martian dust storms subside,) At 10 p.m. CDT, when Mars is near the meridian about 22° up, it may provide excellent telescopic views. Mars moved into the boundaries and in front of the sidereal backdrop of Capricornus.
Brilliant Venus passes about 1 degree from Regulus this evening. Watch as it now pulls away from this star and heads toward Spica. That conjunction is at the end of August.
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Look for 5 planets during the month. From mid-northern latitudes, they are not visible simultaneously. Look for Mercury about 30 minutes after sunset with binoculars, then wait for Mars to cross the southeastern horizon. Four bright planets then span the sky from Mars to Venus. Mars reaches its opposition later in the month. The planet is closer than it’s been since 2003.
