Astronomy From Your Backyard - 9/22 to 9/28 2010
Thursday, September 23 2010 @ 12:48 pm EDT
Contributed by: dgrosvold
By Dave Grosvold
Wednesday evening, Jupiter and Uranus were almost directly below the full Harvest Moon, which is officially full at 4:18 AM CDT Thursday morning. Also on Wednesday evening, the Autumn Equinox for the Northern Hemisphere occurred at 10:09 PM CDT. This time of year, the equinox marks the beginning of Autumn at the point when daylight and darkness are the same length. The Full Moon closest to (either preceding or following) the Autumn Equinox is known as the Harvest Moon. In any given year, the Harvest Moon can occur as early as September 8th, or as late as October 7th.
This year, however, the Harvest Moon and the Autumn Equinox occur on the same night. Some astronomers refer to this event as a Super Harvest Moon. The coincidence of these two events happens about once every twenty years, and so the event is relatively rare. The “Super Harvest Moon” nickname seems to be a relatively recent invention, but as young as it is, it has made its way into the media this year.
One unusual aspect of a Super Harvest Moon is that “twilight” is truly what the term implies — two separate light sources, the Sun and the Moon, are directly opposite one another in the sky. Therefore the Earth is bathed completely in light from both sides. As a result, the evening light takes on an unusual appearance, and can be seen for about three days surrounding the Equinox.
Jupiter and Uranus are still very close together this week and can be spotted in a wide-field telescope or binoculars. See if you can pick out the Galilean Moons in a pair of binoculars as well.
This time of year after nightfall, the dim Little Dipper (Ursa Minor) is upside down (you'll need a fairly dark sky,) and looks like it's dumping water into the bowl of the Big Dipper (Ursa Major) far below it. Perhaps this is a harbinger of the coming autumn rains!
Venus, is very low in the southwest during brighter part of twilight. It sets before dark, but is visible as it is at its brightest point of the year at magnitude -4.8. Mars is quite a bit dimmer than Venus at magnitude 1.5, and is 6° or 7° to Venus's upper right all week. A pair of binoculars may mean the difference between spotting Mars or not.
Mercury is brightening from magnitude 0.0 to –0.8. Look for it low in the east about 45 minutes before sunrise. Look for Regulus twinkling above or to the upper right of Mercury, rising higher every morning. Regulus marks the base of the Sickle, an asterism in the constellation Leo.
Neptune and Uranus are both visible in the evening sky this week, but may take some patience to spot. As mentioned earlier, Uranus is very close to Jupiter and can be easily found in binoculars. Neptune, however, will probably require higher magnification. See last week's Backyard Astronomy article for help in finding Neptune.
On Monday and Tuesday evening, the waning gibbous Moon will not rise until after 9:00 PM, giving us a wonderful opportunity to get a good view of NGC 869 and NGC 884, a pair known as the Double Cluster, in the constellation Perseus. The Double Cluster is a beautiful pair of large open clusters that are actually visible to the naked eye when viewed from a dark sky. They can be found in the seemingly empty space between Perseus and Cassiopeia in the northeastern sky. A low-power view through binoculars or a telescope reveals a myriad of tiny points of light sparkling in the darkness. A beautiful sight for anyone!