The Montana Night Sky
The highlights of the Montana night sky in September are provided by the four bright planets, Venus, Jupiter, Saturn and Mars, shining prominently in the evening sky and the fifth bright planet, speedy Mercury, making a brief appearance in the morning sky during the first part of the month.
As the month begins and the sky darkens after sunset, look for brilliant Venus low in the western sky. Venus is at it brightest on September 21 as it comes closer and closer to Earth, but it is also very low in the sky by this time of the month when it first becomes visible after sunset. Venus sets about an hour and a quarter after sunset as the month begins, but it sets just over a half hour after sunset as September comes to a close.
To the east of Venus, look for the giant planet Jupiter high up in the southwestern sky. Jupiter is accompanied by the much fainter but brightest star in the constellation Libra. Jupiter sets about 10:35 p.m. as September begins and about 8:55 p.m. as September ends.
Further east from Jupiter, look for Saturn in the southern sky above the teapot shape formed by the constellation Sagittarius. Saturn doesn’t set until about 1:20 a.m. as the month begins and about 11:25 p.m. as the month ends.
Turning further east from Saturn, shining brightly in the south-southeast is the Red Planet, Mars. Mars begins the month brighter than Jupiter, but by the end of the first week in September, its brightness has faded to the point that Jupiter becomes brighter than Mars. Mars continues to fade in brightness as the month progresses and Mars speeds rapidly away from Earth after its closest approach to Earth in 15 years in late July. Mars sets at 3 a.m. as September begins and about 1:50 a.m. as the month comes to a close.
After Mars sets, there are no planets to see until tiny Mercury makes a brief appearance in the early morning hours during the first few days of September. Mercury rises about 5:20 a.m. as September begins, but is lost in the solar glare by about September 11.
As for the moon, the moon passes to the upper right of Venus on September 12 and to the upper right of Jupiter the next evening. The moon passes to the upper left of Saturn on September 17 and is located above Mars on September 19. The moon is full on September 24. The moon passes very close to Aldebaran, the brightest star in the constellation Taurus, on September 29.
The Sun arrives at the autumnal equinox at 7:54 p.m. on September 22, when the Sun heads south across the celestial equator and autumn begins in the Northern Hemisphere.
For meteor shower watchers, there are no major meteor showers this month. However, a sporadic meteor can flash across the sky at any time. From a dark site, meteors typically can be seen at a rate of about 5 meteors per hour.