Champaign-Urbana Astronomical Society
It’s tough having all these planets in the sky and we can’t really share them with anyone. If we start (like we usually do) in the evening sky, technically Mercury is above the horizon this month, but it’s not a good look. All month Mercury sets roughly 45 minutes after the Sun and, by the time it’s dark enough to see it, it’s very low. The upcoming morning view in November will be much better. If you want to give it a shot, find an unobstructed western horizon and start looking as the first stars appear. Mercury begins the month just a bit to the right of west, but, as the month progresses, it will follow a relatively flat path to the left. It’s a little better later in September. Greatest separation from the Sun occurs on October 1 but the view doesn’t change much.
Of course, Jupiter and Saturn still command our attention in the south after sunset. They are separated about eight degrees with Jupiter being the brighter of the two and on the right. Both planets will stop their retrograde (east to west) motion this month, Jupiter on the 12th and Saturn on the 29th. They will now slowly close on each other ahead of December’s “super conjunction.” Both planets fade a bit (Jupiter from magnitude -2.6 to -2.4 and Saturn from +0.3 to +0.5) but they are still easily visible to the unaided eye. Now is the time to check them out telescopically if you haven’t already as both transit the meridian near the end of evening twilight. The waxing gibbous Moon will pay them a visit on the 24th and 25th.
Mars is becoming more and more prominent each night as the Earth gets closer. Though the big opposition is next month, Mars rises at 9:30pm CDT to begin September but this time decreases to 7:30pm by month’s end. Mars is in the far eastern corner of Pisces and will be the brightest star-like object in the area with its patented red color. Mars begins its retrograde motion on the 16th. You can chart the position of Mars against the fainter (and farther) background stars every week or so and watch this backwards motion. Mars isn’t really going backwards in its orbit, but it appears to as the Earth passes it in its faster orbit. The same thing happens on an interstate highway when you pass a slower car. The brightness of Mars continues to increase from magnitude -1.8 to -2.5 this month and its angular diameter increases from 19 to 22 arc seconds – large enough to see some surface detail. On the evening of September 5th, watch a waning gibbous Moon rise only a half degree from Mars. The pair will rise nearly due east just after 9:30pm.
Venus was separated farthest from the Sun last month so now it gets closer to the horizon through the end of the year. The rise time for Venus varies from 2:45am early to 3:30am (CDT) later in the month. As Venus crosses the constellation Cancer, a thin crescent Moon catches up with it on the morning of the 14th.
And for those with good charts or a go-to telescope mount, Neptune reaches opposition on the 11th. At magnitude 7.8, it’s still pretty faint but within reach of a modest telescope. Look for it in eastern Aquarius, below the westernmost fish of Pisces. The autumn equinox occurs at 8:31am on September 22nd. On this day, the Sun is directly above the Earth’s equator and 50 degrees high at noon for us. The Sun will rise due east and set due west.
Two other events to mention this month . . . . the waxing crescent Moon will occult the star Beta Scorpii (a wide double star) on the evening of the 21st. Look lower in the southwest before 8:45pm. Use binoculars or a telescope and watch the stars blink out behind the Moon’s dark limb. Also, the magazines are reporting that Comet Howell will be visible in Scorpius this month. At 9th magnitude, it won’t be the attention-getter that NEOWISE was, but it’s still worth a look. The comet was discovered in 1981 and takes 5.5 years to make a trek around the Sun. Look above Sigma Scorpii (the naked eye star to the right of Antares) on the 24th and then a degree north of Antares on the 26th, which is also the comet’s perihelion date. Watch it move from
right to left in our sky. The chart is courtesy of Sky & Telescope magazine. Good luck! Let us know if you see it!