Venus has been remarkably consistent all summer long, emerging as a brilliant light in the western sky at dusk and setting just before 9 p.m. This trend continues in September. Look for Venus as it gets dark (7:30 p.m. at the start of September; 7 p.m. by the end of the month). Venus is that airplane- like dot about a quarter of the way up in the west as it gets dark. Whenever Venus is in the sky, it is always the brightest dot of light. Venus sets just before 8:45 p.m. throughout September.
On Sept. 3, it is right next to the bright star Spica. This is a good night to get a sense for just how much brighter Venus is than even bright stars like Spica. Since Spica shines at first magnitude and Venus shines at minus 4 magnitude, that means that Venus is about 100 times brighter than Spica.
Saturn has been a constant companion in our midevening skies all summer, but its time is coming to an end. Throughout the month, Saturn will appear lower and lower in the west as it gets dark, and will be almost gone by Sept. 30.
At the start of September, look for Saturn about a third of the way up in the west at dusk. It has a slightly whiteyellow color. If you are out in the early evening, before 8:30 p.m., find blazing Venus first, well below Saturn. The star Spica will be above and to the left of Venus, and the planet Saturn will be above Spica. Here in early September, Saturn sets in the west around 9:45 p.m.
By Sept. 6, Venus will have moved above Spica and you can find Saturn from Sept. 615 by looking above Venus. By mid-September Saturn is only a quarter of the way up in the west at dusk and sets by 8:45 p.m.
For the last half of the month, Saturn is lower at dusk; by Sept. 30 the planet is only one hands width above the west horizon at dusk and is gone just after 8 p.m. Venus, again your handy guide for finding dimmer Saturn, is just to the left of Saturn on Sept. 20. From Sept. 21 to the end of the month, again find Venus first, then look down and to the right for Saturn.
CELESTIAL GATHERINGS
The most striking astronomy sight in September is the ballet of Venus, Saturn, the moon and (at the end of September) Mercury. Here are a few of the best viewing nights.
>> Sept. 7: Look low in the west between 7:30 and 8 p.m. for the beautiful sight of a slender crescent moon down below Venus, near the western horizon. The moon will be about 5 degrees below Venus, or a little more than the width of two fingers held at arms length. Also, look for the bright, slightly blue star Spica appearing between Venus and the moon on this night. Finally, look about 10 degrees above Venus (the width of a hand at arms length) and slightly to the left to find Saturn.
>> Sept. 8: Venus, Spica and Saturn remain in the same place as on Sept. 7, but now the crescent moon has moved just above Venus and lies between Venus and Saturn.
>> Sept. 9: Spica, Venus and Saturn still pretty much are in same place as the two previous nights, but now the somewhat fatter crescent moon is just to the left of Saturn.
>> Sept. 14-15: Look for brilliant Venus low in the west at 8 p.m. Look directly above Venus for Saturn, just 4 degrees (the width of two fingers at arms length) above Venus. For the ensuing week, Venus will pass to the lower left of Saturn, until:
>> Sept. 21: Look for Venus and Saturn side by side, around 8 p.m.; Venus is the one on the left and far brighter than Saturn. The planets are 5 degrees apart. For the rest of the month, Venus will appear farther away from Saturn, to Saturns left, night by night; by Sept. 30 Venus is a full fists diameter to the upper left of Saturn and sets later than the ringed planet. Saturn is down at 8 p.m. on Sept. 30 and Venus by 8:40 p.m.
>> Sept. 27-30: For the last few days of the month, if you look west at 7 p.m., you might be able to catch Mercury just above the western horizon. Find Saturn, then look about 10 degrees below Saturn for Mercury, shining at minus 0.07 magnitude. Youll need a flat west horizon; it only gets dark enough to see Mercury around 7 p.m. and the planet sets by 7:30 p.m.
JUPITER AND MARS
Jupiter is by far the brightest morning planet this September. If you are an early riser or late-to-bedder, the eastern sky is beautiful, with Jupiter backed by the brilliant stars of winter.
At the start of the month, Jupiter rises at 2:15 a.m. in the east-northeast. Jupiter is halfway up in the eastern sky at daybreak in early September. By the end of September, Jupiter rises at 12:30 a.m. and is two-thirds of the way up in the east at daybreak. Jupiter is brighter than any other dot in the morning sky.
While Jupiter is the brightest dot of light in the morning, it is also accompanied by the brilliant winter stars. Jupiter is in the constellation of Gemini, with its bright stars Castor and Pollux. Look for the waning crescent moon next to Jupiter early in the morning of Sept 28.
Mars remains pretty dim in the morning sky. Your best shot at finding Mars may be before dawn on Sept. 1; find the waning crescent moon around 4 a.m. in the east, and look about 7 degrees to the lower left of the moon. That ruddy spark is Mars.
