Evan Hazard/Northland Stargazing: Planets and a 'comet of the century'
September starts with Saturn above and left of brighter Venus in the WSW, and Spica below and right of Venus. But Saturn rapidly moves sunward, passing 3.5° above Venus on Sept. 17-18. Mercury is too low after sunset for easy viewing. However, try binocs a half hour after sunset Sept. 24. Bright Venus and dimmer Saturn will be well above the horizon, with Mercury to their lower right just 0.75° above dimmer Spica.
Sol crosses the celestial equator at 3:44 pm Sept. 22, marking the start of astronomical autumn. This is also when the daily progression of the stars seems slowest. Sol sets three to four earlier every day, dusk thus coming earlier, so we will see familiar stars longer. Vega (in Lyra), brightest star in the "summer triangle," is right overhead. The next brightest is Altair (in Aquila), well to the SSE, and then less bright Deneb, actually the largest but farthest of the three, not far to the ENE, in Cygnus.
The other two easy naked eye planets are for night owls and early risers. Jupiter rises after midnight, so is high in the sky before dawn. Mars rises about 3 a.m., so is an easy object before sun up. Mars passes in front of my favorite open cluster, M45, the Beehive, the mornings of Sept. 8-9. Use binocs to see individual stars in the Beehive.
Comet C/2012 S1 ISON passes 2.0° north of Mars Sept. 27. ISON may be a bright enough fuzzy "star" by then to detect just above Mars.
ISON (International Scientific Optical Network) is another example of media hype -- some outlets hale any new comet as possible "comet of the century." Discovered last winter, its orbit is highly elongate and this trip will take it very near Sol, perhaps for the first time. Our orbit put Sol between ISON and us last May. Visible again, it has not brightened as much as expected but, if it is new to the inner solar system, it may still have a lot of volatiles that might put on a good show.
ISON will reach naked-eye visibility about Nov. 10 but it will soon disappear into the morning twilight as it rounds the far side of Sol. If Sol does not disrupt it completely, it may appear in the pre-dawn sky with a strong tail in early December.
Perseus is low above the NE horizon at dusk, so it's Algol-watching time again. The only minima of Algol you will likely be up for are at 12:34 a.m. Sept. 15-16 and 9:23 p.m. Sept.18. Thus, Algol will be perceptibly dimmed for about two hours centered on midnight Sept. 15-16 and 9:30 p.m. Sept. 18. Other constellations next time.
Hazard, a retired BSU biology professor, also writes "Threescore and Ten" for The Pioneer's "Prime Time."