Evening Planets — Saturn swiftly sinks and Mars rules
Saturn is very low in the southwest tonight. Look just after sunset to spot an extra “star” in Sagittarius. That’s Saturn. The ringed world will have a lunar visitor on Dec. 8. The moon will be an ultra-thin crescent about 1 ½ degrees below and to the right of Saturn. Saturn slips quickly into the sunset’s glare by Dec. 14.
Mars is the brightest evening planet this month. Venus and Jupiter have plunged from the evening sky. Earth is speeding away from the red world so that Mars appears to be dimming and shrinking rapidly. Telescope observers will notice Mars apparent diameter shrinking by nearly 20 percent this month. Surface features will be very difficult to discern by mid-month. Each night, Mars slides a bit toward the east and slowly overtakes pokey Neptune. Mars and Neptune will have a conjunction on Dec. 6, passing a little less than one half a moon width apart. Binocular users will easily find bright Mars and therefore can spot 7.9 magnitude Neptune nearby.
Without a bright beacon nearby, gas giant Uranus will be more difficult to spy that Neptune. A handy star chart can be found in the September 2018 issue of Sky and Telescope magazine. Uranus, at magnitude 5.7, is technically a naked-eye object this month. Look in Pisces near the Aquarius border to spot Uranus.
Dawn Planets — A dawn gathering of bright planets
Venus continues to race away from the rising sun. Each morning, Venus rises a bit earlier than the sun. Monday morning, Venus blazes above the southeast horizon just after 4 a.m., nearly 3 ½ hours before the sun. A little over two hours later, Mercury pops above the eastern horizon followed by bright Jupiter barely 30 minutes ahead of sunrise.
An old crescent moon visits Mercury on the morning of Dec. 5 and Jupiter the next morning. Mercury reaches maximum elevation on the morning of Dec. 11, about 8 degrees above Jupiter. By mid-month, Mercury begins to slip as Jupiter ascends. Both worlds are about two hours ahead of the sunrise. Jupiter appears to pass by Mercury on the mornings of Dec. 21 and 22. The largest and the smallest planet seem to pass just over a moon width apart on the morning of Dec. 21. Jupiter continues to rise and Mercury sink. As 2018 closes, Venus rises nearly four hours before the sun; while Jupiter rises more than two hours ahead of sunrise and Mercury slightly more than one hour before the dawn twilight.
A bright Comet, a major Meteor Shower and a demoted Planet
A comet discovered in 1948 by American astronomer Carl Wirtanen is streaking into the inner solar system this winter. This is one of the most favorable visits of this periodic comet. Tonight, look to the east-southeast in the constellation Cetus near Pi Ceti and the Eridanus border to spot a small fuzzy spot. That is Comet Wirtanen. About every 5 ½ years, Comet Wirtanen circles the sun, but this may be the brightest appearance in many decades.
Although not expected to be a great comet like the famous Hale-Bopp, Comet Wirtanen should be easy to spot without optical aide from a dark observing site. Forecasts estimate the comet will achieve fifth magnitude or better by mid-December. Three other small and much dimmer comets will also grace December skies for telescope observers. Comets Atlas, Stephan-Oterma and Swift-Gehrels will shine at between ninth and tenth magnitude in the evening skies. Come to the Morgan Observatory on Dec. 13 to see these comets, weather permitting.
December brings the seldom observed Geminds Meteor Shower, a rival of the August Perseids shower. Cross your fingers for clear nights on Dec. 12 to 14 to see dozens of Geminid meteors zip across the night sky. The Geminids are forecast to peak at 4:30 a.m. on Dec. 14, but our 100 valleys of the Umpqua are notorious for foggy mornings. If we do get a clear morning on Dec. 14, about 100 meteors are expected between 4:30 and 5:30 a.m. Bundle up, since fog-free December mornings can be very chilly.
Perhaps a better strategy to enjoy the Geminids in the Umpqua Valley is to forego peak predawn rates. Geminids will be streaking across the sky as early as 9 p.m. Look toward the northeast or southeast after 9 p.m. to spot 30 or 40 meteors per hour. A fat crescent moon will be low in the night sky until 11 p.m., but it will be easy to block for early observing. A Geminids observing session will be hosted at the Morgan Observatory starting at 8p.m. if skies clear.
Asteroid Juno was discovered in 1804 and was once considered the sixth planet from the sun until 1845. It will make a rare close encounter with Earth this month. This will be the closest opposition of Juno in 13 years and will not be equaled until 2060. Juno can be found in the constellation Eridanus at 7.6 magnitude tonight, and the 73 mile-wide asteroid will slowly fade to 8.1 by January 2019. Until late December, Juno will outshine the planet Neptune and can be seen in binoculars. Look to the lower left of Menkar (Alpha Ceti) by about 10 degrees to seek Juno. A star chart will reveal Juno’s position.
Paul Morgan Observatory at UCC
Come to the observatory on the evening of Dec. 13 at 8 p.m. to observe the annual Geminid Meteor Shower, Comet Wirtanen and much more. Please check the observatory website at umpqua.edu/observatory for updates.
A special short video program will be offered if skies are cloudy. Observatory seating is limited, and parking is available near the Tower Building at UCC. All events are offered without charge. Dress warmly, as the nights can be very chilly at the observatory.
Umpqua Astronomers Meeting — January 2019
Come on 7 p.m. Jan. 8 to UCC Wayne Crooch Hall, Room 18, for the Umpqua Astronomers January 2019 meeting. Club news, monthly sky events and astronomy news will be presented. The astronomical events for 2019 will be discussed. Everyone interested in astronomy is welcome. Newcomers to astronomy are invited to a special pre-meeting at 6:30 p.m. to ask questions and learn about beginning astronomy. For more information visit, umpquaastronomers.org or call 541-673-1081.