Comets dominate the pre-dawn skies and their flybys of neighboring planets offer observing challenges for early bird sky-gazers.
Comet ISON Brightens. Late last week Comet ISON began to wake up and now shines ten times brighter than it did just a week earlier. At magnitude 5.5 it has finally reached naked-eye levels from dark locations, according to observers around the world. (The lower the magnitude number, the brighter the object.) Even so, watching the phenomenon with binoculars and telescopes is the best way to witness this celestial body. (See also: “New Comet Discovered—May Become ‘One of Brightest in History.'”)
The sudden brightening is due most likely to vaporization of surface ice, leaving the comet sporting multiple tails— with the longest stretching some five million miles (eight million kilometers) out into space. That’s equal to more than 21 times the distance between Earth and the moon.
What will ISON do next is anyone’s guess, but all this activity makes it worth watching as it approaches its close encounter with the sun on November 28.
Look for the comet near the bright star Spica low in the southeast about an hour before your local sunrise. ISON is now visible from both Northern and Southern Hemispheres. (Related: “Comet ISON: Pop or Fizzle?“)
Moon and Aldebaran. Look toward the low eastern sky on Monday evening, November 18, for the near full moon parked near the bright orange star Aldebaran. The pair will appear less than four degrees from each other in the sky—about the width of three middle fingers at arm’s length.
Aldebaran, the lead member of the constellation Taurus, sits some 65 light-years from Earth and has a diameter 30 times that of our sun. The red eye of the bull is so large that if we would replace our sun with Aldebaran its outer atmosphere would reach Mercury’s orbit.
Comet Encke passes Mercury. For those with an unobstructed view of the southeastern horizon before local dawn on Tuesday, November 19, try hunting down Comet Encke. It will appear to be passing by the faint planet Mercury in the constellation Virgo. A binocular and telescope target from the Northern Hemisphere, this icy interloper glows at magnitude 7 and will be less than five degrees northwest of the innermost planet of the solar system.
Encke was first spotted in 1786 and it rounds the sun in only 3.3 years—making it the shortest period of any known comet. On November 21 it will make its 62nd recorded perihelion—or closest approach to the sun.
As both comets, Encke and ISON, head for their close encounters with the sun later this month, they will be caught on camera for the first time by NASA’s Mercury orbiter, MESSENGER.
Detailed finder skymaps of both comets can be found at cometchasing.skyhound.com.
Gemini-Moon-Orion Align. Late night on Wednesday, November 20, offers sky-watchers a great chance to track down two bright constellations using the moon as a guidepost. While the bright waning gibbous moon’s glare will block out most faint stars in the eastern sky, two bright stars, Castor and Pollux, will appear to the left of the moon along with Jupiter below the twin stars of Gemini. To the right of the moon is the bright orange star Betelgeuse and Rigel marking out Orion, the hunter. (Learn more about the solar system.)
Jupiter Joins the Moon. By nightfall on Thursday, November 21, the largest planet in the solar system, Jupiter, appears as a brilliant beacon in the east rising together with the moon. The two worlds will be separated by only five degrees, a little more than the width of three fingers at arm’s length.
Mercury and Saturn. On Sunday, November 24, right through the new week look toward the low southeastern sky about 30 minutes before sunrise for Mercury and Saturn to pass very close to each other. The ringed world appears the brighter of the two and lower left of Mercury. The next two mornings will see the two planets switch places as Saturn continues to rise and Mercury sinks slowly towards the sun.
ISON Passes Planets. As an added observing challenge in the Sunday morning twilight try also spotting comet ISON lower right of the planetary pair. This may be one of the last mornings the comet may be visible from Earth as it dives towards its close encounter with the sun on the 28th.