October is not a great month for planet observing. Mercury and Jupiter are both pretty much out of sight for much of the month. Saturn is in view, albeit quite low an hour after sundown (only about 20 degrees high for mid-northern latitudes) in the southwestern evening sky. In the morning sky we can look for Venus and Mars very low in the eastern sky, engage in a rather tight conjunction on Oct. 5th, though you'll probably need binoculars to help you see Mars against the bright backdrop of dawn. Mars will be easier to see late in the month when it climbs higher and gets a chance to be seen against a darker sky.
In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm's length measures roughly 10 degrees. Here, we present a schedule below which provides some of the best planet viewing times as well directing you as to where to look to see them.
Mercury — is in superior conjunction on Oct. 8th, on the far side of the sun this month and is not visible. Even later this month this speedy planet is too low in the Sun's afterglow to be seen at dusk, even as it draws away from the sun, unless you live south of the equator. From there, the planet appears much higher in the western sky and should be easy to spot . . . if you live in Bogota, Johannesburg or Melbourne . . . by month's end.
Venus — In the dawn sky, is a brilliant light that sinks closer to the eastern horizon as it retreats to the far side of the sun. Venus rises just before the first gleam of morning twilight throughout most of October. But Mars climbs higher each morning as we start catching up with it. On the morning of Oct. 5th, look 10 degrees above the eastern horizon at around 6 a.m. local daylight time to see these two planets pass outstandingly close to each other. In the Eastern U.S. they are separated 0.27-degree -- about half the apparent width of the moon. The Western U.S. sees them even closer: 0.22-degree. Casual skywatchers can easily miss this pairing, however, since Mars is 191 times fainter! Mars hovers to the lower right of Venus. By Halloween Mars is 16 degrees to the upper right of Venus.
Mars — continues to flee ahead of Earth in orbit around the sun and rises around 5 a.m. all month. Still on the far side of the sun, this 2nd-magnitude planet displays a tiny disk even in moderately large telescopes. But our world is slowly gaining on the red planet, and, as we do so, Mars climbs higher each day into the eastern sky. Early on the morning of Oct. 17th, a very narrow (6 percent illuminated) crescent moon lies only 1.3 degrees to the left of Mars, while 8 degrees below them brilliant Venus blazes.
Jupiter — may still be glimpsed in the opening days of October very low near the west-southwest horizon after sunset. Bring binoculars. But for the rest of the month, it's impossible to see thanks to its proximity in the sky to the sun. Jupiter is in conjunction with the sun on Oct. 26th, and transitions into the morning sky.
Saturn — in Ophiuchus is still feebly signaling for attention as it slides offstage in the southwest. Look for it on the evening of Oct. 24th, hovering well down to the lower right of the waxing crescent moon. It glimmers into view during twilight low in the southwest, followed a few minutes later by slightly dimmer Antares about 13 degrees to its lower right. The rings are now at their widest since April 2003 with the north face now tilted nearly 27 degrees to our line of sight. Unfortunately, through a telescope the planet's image likely will be shivering and churning about in the poor seeing near the horizon. Saturn sets about four hours behind the sun early in the month, 2½ hours after sunset by month's end. The ringed planet is now at its faintest for this year, magnitude +0.5, and is now over 87 light-minutes away. Both Saturn and Antares will vanish into the twilight next month.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications, and he is also an on-camera meteorologist for Fios1 News in Rye Brook, NY.