The Sky This Week, 2013 October 15 - 22
Jupiter, with Io and the Great Red Spot
The Moon brightens the evening sky this week, climbing through the dim autumnal constellations before finishing the week among the rising stars of winter. Full Moon occurs on the 18th at 7:38 pm Eastern Daylight Time. October’s Full Moon is almost universally known as the Hunter’s Moon, and it gets this name thanks to its similar orbital geometry to the Harvest Moon. For several nights around the time of Full Moon the Moon will rise 35 to 40 minutes later each night at the latitude of Washington. The farther north you go, the closer the intervals are, so folks who live in Scotland will see about a 20 minute interval. Icelanders see the Moon rise about 10 minutes later each night, while folks north of the Arctic Circle will see it rise a few minutes earlier! Just as legend has it that the Harvest Moon gave Northern Hemisphere farmers more light to aid in their harvests, the Hunter’s Moon gave more light to hunters pursuing game across the stubble of the harvested fields. Look for Luna near the bright star Aldebaran late in the evening on the 21st.
This year’s harvest Moon brings a treat for east coast skywatchers since it also happens to be the time of a penumbral lunar eclipse. As Luna rises on the evening of the 18th her southern limb dips deeply into the Earth’s penumbral shadow. She crests the horizon here in Washington at 6:14 pm EDT with the eclipse underway. Maximum eclipse occurs at 7:50 pm. At this time you should notice a distinct darkening of the bottom of Luna’s disc. The shading will be quite subtle, but it should be readily apparent when compared to the northern limb. The darkening will then slowly shift to the southwestern limb before the eclipse ends at 9:52 pm.
The eclipse won’t darken the Moon’s overall glare that much, which means the sky will be quite bright for most of the week. For the skywatcher with binoculars or a small telescope the pickings are pretty much limited to bright stars and asterisms, but it can be quite entertaining just to look at different stars for their subtle differences in color. The dazzling blue tint of the bright star Vega in the Summer Triangle contrasts nicely with the white of the star Altair, while the latter has an even more dramatic contrast with the star Tarazed, just northwest of Altair in the same binocular field. If you have a small telescope, see if you can track down the long-period variable star T Lyrae, about two degrees southwest of the aforementioned Vega. This star is a fine example of a type of variable known as a "carbon star", and it is one of the reddest-tinted stars in the sky.
Venus is gradually becoming more prominent in the western sky during evening twilight, and the dazzling planet is gradually gaining altitude with respect to the horizon. She now sets just over two hours after the Sun and gains a minute or two on Old Sol each successive night. If you have a good view to the west you can spot her against a dark sky half an hour before sunset.
Giant Jupiter is steadily making progress toward the evening sky. By the end of the week Old Jove rises at around 11:00 pm along with the bright stars of the Great Winter Circle. If you’re up in the early morning you should have no trouble spotting him among his bright companions. Pre-dawn observers will find him ideally positioned close to the meridian as morning twilight begins to brighten the sky. This is the best time to observe Jupiter’s turbulent cloud features; early morning air is usually the steadiest of the day, allowing subtle features to be seen in very modest telescopes. Jupiter’s most famous feature, the Great Red Spot, should be well-placed on his disc at 6:00 am EDT on the mornings of the 15th and 21st.
Mars shares the morning limelight with Jupiter and can be easily seen about halfway between Old Jove and the horizon. Earth is gradually catching up to the red planet, so over the next few months he will slowly brighten and his disc will begin to increase in apparent size. I’ve already had a few peeks at him before dawn, and in moments of very steady air several of his larger surface features are becoming apparent.