Sky Lights ~ Libra
September 22 - October 23, 2010
Venus and Mars are sinking in altitude toward the light of the Sun. Venus sets at the beginning of Libra at 8:00pm and Mars 30 minutes later. At the end of Libra, Venus sets with the Sun and Mars sets about 45 minutes after sunset. Venus retrograde (10/8-11/17) is in inferior conjunction 10/28. Venus, moving closer to Earth, is growing bigger and brighter, while Mars, moving away, is negligibly diminishing in size and brightness. Venus at magnitude -4.8 pierces the twilit sky and briefly blazes low on the southwestern horizon. Dim Mars at magnitude 1.5 is challenging to see at dusk. Venus and Mars pair up near the star Zubenelgenubi (zoo-BEN-al-je-NEW-bee) in the constellation Libra. These 3 celestial bodies form a difficult to see shapeshifting triangle in the southwest just after sunset. Zubenelgenubi at magnitude 2.7 is quite a bit dimmer than the planets and may be impossible to see without the right optical aid. Best viewing opportunities occur in September if you have clear skies, an unobstructed horizon and right timing; binoculars are helpful in drawing these celestial bodies out of the twilight. Venus is at its greatest brilliancy 9/23, setting an hour after the Sun. 9/23 7:30pm Map (The Zuben-star lies above and closest to Venus.) October viewing is more challenging as the planets sink lower and set earlier. The further south your location the higher these planets appear. 10/1 Venus and Mars are in close proximity. 10/1 7:30pm Map 10/3 Venus and Mars are in exact conjunction. 10/9 young Luna nestles between the two. 10/9 Map (Mars lies to the left of the Zuben-star.) Venus has phases like the Moon; you can see them and more in this Venus 2010 Animation. As Venus gets closer to Earth and bigger in disk size its illuminated phase decreases; during Libra Venus wanes from a 27% - 2% illuminated Crescent. You can see this demonstrated in APOD's animation of the phases of Venus and in this montage.
Jupiter remains at its best during Libra having reached opposition 9/21. During this time the planet lies closer to Earth than it has in 47 years, resulting in its appearance being bigger and brighter than it has been in a long time. Look for Jupiter in the southeast not long after sunset. The planet travels high above the southern horizon as the night progresses. Jupiter sets in the west at 6:30am in the beginning of Libra and at 5:00am by its end. At magnitude -2.9 the planet is the brightest point of light in the night sky after Venus sets. During Libra, in the dim constellation of Pisces, Jupiter pairs up with Uranus, which like Jupiter is at its closest, biggest and brightest for 2010. Uranus at magnitude 5.7 is now easily seen with binoculars and without an optical aid in a dark sky. Uranus and Jupiter, in exact conjunction Sept. 18/19, are in close proximity to each other and to the Harvest Full Moon. 9/23 9pm Map Jupiter is retrograde 7/23-11/17.
Mercury appears above the sunrise horizon and brightens with each new day, however it is now sinking back toward the Sun having achieved greatest elongation and a best morning performance 9/19. Elusive Mercury rises in the beginning of Libra at 5:45am. 10/1 the planet lies 5º above the eastern horizon and can be seen piercing the morning twilight 30 minutes before sunrise. During the first week of October Mercury rapidly sinks out of sight. By 10/16 the planet is in superior conjunction.
Saturn reappears in the morning sky shortly before dawn as Libra comes to an end. Easier viewing of the planet occurs at the end of October.
Vega is the brightest star overhead as night falls. It is the western point of the Summer Triangle and sets well after midnight. Altair is the triangle's southern point and Deneb the eastern point. The Milky Way sweeps through this triangle from teapot-shaped Sagittarius in the southwest to M or W-shaped Cassiopeia the northeast.
The Keystone of Hercules is a fat, four star trapezoid or wedge located about a third of the way from Vega to Arcturus. Draco now lies to the north of Vega and Hercules. The Big Dipper is north of this Dragon. Star Chart
Fomalhaut is the brightest star low on the southern horizon from 9:00pm to midnight. it is the Southern Royal Star and the brightest star in the constellation Pisces Austrinus south of Aquarius. In 2010 Fomalhaut lines-up diagonally with Jupiter in the night sky. Star Chart
Capella is the bright star rising in the northeast about an hour and a half after sunset. Capella is the brightest star seen the most often.