By Andy Veh, for the Redoubt Reporter
Now it gets dark at a reasonable time in the evening and besides the sun and the moon we can again see planets, the occasional meteor, comets perhaps, stars, some star clusters, and two galaxies.
First, find the Big Dipper low in the northwest, then take the distance between the dipper’s last two stars and extend it five times toward the zenith (the point straight up), and you get to Polaris, the North Star, which is a semibright star at the end of the Little Dipper’s handle. It also marks our latitude on the Kenai Peninsula at 60 degrees above the northern horizon.
Next, find the constellation Cassiopeia, in the shape of a W, on the other side of the Little Dipper, high in the northeast. High in the sky as well, almost in the zenith, is Cygnus, the swan, which also looks like a cross. Its brightest star, Deneb, connects with two other bright stars, Vega and Altair, in the constellations Lyra, the harp, and Aquila, the eagle. Together they make up the prominent summer triangle.
Just left of them is the Great Square of Pegasus, high in the southeast. To its left is the first object you are able to see, ultrabright Jupiter. Turning to the west we can see bright-red Arcturus setting, a sign that summer is over. And rising in the northeast is bright yellow Capella, a corner of Auriga’s pentagon. Throughout the night, all constellations move from east to west (of course, it’s Earth rotating that gives us this illusion). Thus, the evening western constellations set while in the east Taurus, Orion, Gemini and Cancer are rising throughout the night, telling us that winter is coming up.
Mercury is visible on the eastern horizon before dawn, around 5 a.m., with best viewing between Sept. 1 and 10. It’s bright enough to be seen with the unaided eye, but because of low contrast due to its proximity to the horizon and against a brightening morning sky, it’s better to scan the eastern horizon with binoculars. Around Sept. 8 it’s joined by Leo’s Regulus, the two of them making a close pair in a binocular field. It would be joined by the moon later this month, but at that time Mercury will have quickly moved toward superior conjunction — meaning, to the other side of the sun, and thus out of view.
Venus just passed through superior conjunction, so it can’t be viewed in September. Starting in late October it will shine brightly in the evening all winter long.
Mars rises around 1 a.m. in the northeast. If you happen to be up that late, then you can see that September is ideal for viewing a planet’s motion. The red planet moves right to left — west to east, the true direction of the solar system — through Gemini, getting closer to forming a straight line with Gemini’s bright stars Castor and Pollux. Mars approaches from the right, forming an acute triangle with these two stars, making a straight line around Sept. 15, and then moving on toward the left of these two stars.
The third-quarter, almost-crescent moon passes Mars from Sept. 22 to Sept. 23. Mars moves into the pretty Beehive cluster on Sept. 30. You may see this star cluster with the unaided eye, but with bright Mars right next to it, binoculars allow for better contrast.
Jupiter appears low on the eastern horizon after dusk. But it’s, of course, so bright that you will notice it somewhere between the east and the west (relatively high above the southern horizon) each clear night all fall and winter long. The giant planet is joined by the gibbous moon on Sept. 16.
Although Saturn appears at quite some distance from the sun, the two are setting at just about the same time, making Saturn unobservable. It can be viewed prior to dawn starting in early November.
This is a good month to observe Uranus in Pisces and Neptune in Aquarius, both above the southern horizon in the evening. But they appear faint enough that finder charts and binoculars are needed. For detailed finder charts go to nakedeyeplanets.com and click on either planet’s name (this seems to be a really good website) or Google “find uranus neptune chart 2011.” The almost-full moon joins Neptune on Sept. 9 and Uranus on Sept. 12.
A word about the direction of motion in the solar system being west to east: Almost all bodies in the solar system orbit counterclockwise (notable exceptions are Neptune’s moon Triton and a number of small moons of the giant planets). Almost all bodies rotate counterclockwise, as well (a notable exception is Venus).
Since we don’t notice our own Earth’s counterclockwise rotation, and for all practical purposes consider ourselves fixed in space, we get the illusion that everything else seems to move clockwise, which we can easily see as the sun, moon and stars seem to move east to west each day and night. An analogy is to picture yourself sitting on a rotating merry-go-round — you get the illusion that the landscape around you rotates in the opposite direction.
But the true direction of motion, foremost of the moon and planets, can be seen by observing from one night to the next or from one week to the next, as suggested above for Mars moving past Castor and Pollux.
Andy Veh is a professor of astronomy and physics at Kenai Peninsula College’s Kenai River Campus.