EVENTS AND NAKED EYE VIEWING
NOTE: All Sky Charts Courtesy of SkyGuide App Unless Otherwise noted.
December 2 (Sunday) Venus At Greatest Illuminated Extent. Venus has established itself as the "Morning Star" after crossing between Earth and the Sun (called Inferior Conjunction) in late October. The nearest planet to us has sped ahead of Earth once again and will continue to outrun us because Venus takes about 140 days less than Earth does to make one complete orbit around the Sun. This day marks Venus' maximum illumination that it can get in the predawn sky.(magnitude -4.86). It will continue to rise higher each morning but also will get slightly dimmer as it races ahead of us.
This is how the predawn sky will appear facing SSE during Venus' time of greatest illuminated extent. Venus will be a bright beacon of light 15 degrees above the horizon an hour before sunrise. The only object brighter than Venus will be the waning crescent Moon 15 degrees above the "Morning Star" and centered in the constellation Virgo The Maiden. The interesting parallel here is both Venus and the Moon will look identical in crescent phase except that the Moon will be waning while Venus will be waxing. You'll be able to see Venus' crescent shape using a small telescope with a medium to high power eyepiece. Viewing the Moon and Venus this way with the Sun soon to rise gives you a sort of 3D image in your mind as to how we align in our solar system's merry-go-round.
December 6 and 7 (Thursday and Friday) Mars-Neptune Conjunction. Here's an excellent chance to see Neptune using Mars as a guide. Mars is still the brightest object above the southern horizon when the Moon isn't around and these are our lucky nights! There will be a New Moon (completely dark) and Neptune will be within two degrees of Mars. Here's the rub. Mars will be shining 20 times brighter than Neptune so you won't be able to see both of them in the same field of view. Use the following three sky charts and my suggested technique and you may be able to positively identify Neptune using only a pair of 10x50 binoculars mounted on a camera tripod.
The lonely star Fomalhaut and Mars will be the only two bright objects above the southern horizon an hour and fifteen minutes after sunset on December 6 and 7. Look about half way up from the horizon (45 degrees) to see orange-red Mars. Set your binoculars on a camera tripod and center Mars in the Field Of View (FOV),then follow the instructions below.
This is a close up of how Mars will look centered in your binoculars FOV on December 6. You need to move your binoculars to the left until Mars is just outside the FOV. Neptune should then be the brightest object near the center. By using this technique, you eliminate the glare from Mars so you can see much dimmer Neptune. The brightness of Neptune is exaggerated in this image. Neptune through binoculars will look more like the star HD 217265 but Mars brightness is more realistic.
You can confirm that you saw Neptune by viewing Mars the next night (December 7) at the same time (6 PM). By moving your binoculars to the right this time until Mars is just out of view, Neptune will be visible near center again in the binocular FOV. This is not because Neptune has moved. Rather Mars, being much closer to Earth, has appeared to move from west of Neptune to East due to the combined movements of our Earth and Mars in 24 hours. If you wish to photograph Neptune, you can use a DSLR camera instead of binoculars. If you decide to do that, I suggest taking some test shots of Mars and the surrounding photographic field during early December to get an idea of the exposure and ISO settings to use. Exposure times of 10 to 15 seconds and an ISO of 400 to 1000 are good baseline numbers. Keep in mind that exposures greater than 15 seconds usually get blurred because of Earth's rotation. If you intend to keep the shutter open longer than this, you should piggyback your camera on a telescope with a clock drive mount that tracks celestial objects or mount the camera directly on the visual back of your telescope.
December 1 (Saturday) Through December 9 (Sunday) Short Period Comet Wirtanen Brightens. I hardly ever write about comets unless it's possible to see them naked eye. Comet 46P/Wirtanen may fit the bill as December 2018 marks the closest approach ever predicted since its discovery in 1948 and the brightest it may get until at least 20 years from now. That said, it's predicted peak brightness (magnitude 3) is near the naked eye limit of casual observers who do not know the night sky that well. The good news is this comet which is only 3/4 mile in diameter contains lots of volatile gasses along with water ice that'll boil off its surface as it approaches the Sun. The resulting shell of gas and dust will make it look thousands of miles in diameter larger and should make it glow like a ghostly green fuzz ball. This contrasts well with the whitish background stars. Comet Wirtanen's closest approach to Earth will be on December 16, but the glare from the waxing gibbous Moon may wash out the view. That's why I recommend looking for it from the beginning of December until December 9 to avoid interference from the Moon.
This is the daily track for comet 46P/Wirtanen at 7 PM MST with December 5 marking the middle of the best days to view it. Wirtanen's position on December 1 will be where the track line crosses an imaginary vertical line extending above the SE horizon. The comet will probably be at its brightest on December 16 when it will be located directly below the Pleiades star cluster above the eastern horizon. Each dot on the track line marks the comet's movement in a 24 hour period. Happy comet hunting!
December 13 (Thursday) and 14 (Friday) Geminid Meteor Shower. This is the only meteor shower besides the Perseids that is reliable and prolific. The Geminids are not as well known as the Perseids because of the time of the year. The Perseids are in August when nights are comfortably cool while the Geminids are in December when most of us do not care to spend much time at night outside, especially during the very early morning hours when this shower will be at it's peak. The predicted peak this year is from 5 to 6 AM MST on December 14. So if you are an early riser, throw a warm coat over your jammies and step outside (hopefully at a dark sky location) to scan the sky for as many as 120 meteors per hour. If you're not a morning person, you can view them the previous night when Gemini rises above the NE horizon at 7 PM MST on December 13 and will be directly overhead by 1 AM MST on December 14. As is true with almost all meteor showers, the best time to view them is during the early morning hours when the Earth is orbiting and turning eastward into the meteor stream. This increases the rate and speed that the meteors strike Earth's atmosphere. It's also a good idea to lie flat on a lounge chair or blanket in an area that provides the greatest panoramic view of the sky. Meteors can appear anywhere in the sky even though all of them can be traced back to a single point or radiant. In this case, the radiant is very close to the star Castor in the constellation Gemini The Twins.
December 15 (Saturday) Mercury at Greatest Elongation West of the Sun (21 degrees). Mercury is never far from the Sun which makes it difficult to observe except during times of greatest elongation (greatest angle east or west of the Sun). On this day, greatest elongation will occur in the predawn sky at 5 AM MST. However, it'll be in its best viewing position at 6 AM on December 12 when it'll be almost 7 degrees above the horizon one hour before sunrise. I'm splitting hairs here because Mercury will be in practically the same position in the predawn sky (give or take 1/4 of a degree) from December 12-15. Even though Mercury is a bit less than 1 1/2 times the size of Earth's Moon, It's bright enough to see naked eye. Mercury takes on a reddish tint because of the color of Earth's atmosphere close to the horizon.
Venus dominates the eastern predawn sky, so find it first then scan down and to the left to find Mercury shining only 1/7 as bright as Venus. For folks with a flat unobstructed view of the eastern horizon, you may see Jupiter right on the horizon line below Mercury.
December 21 (Friday) Winter Solstice. At 3:23 PM MST, the Sun will reach its farthest point south in the sky as Earth reaches its maximum tilt away from the Sun. All areas north of the arctic circle will not have the Sun in the sky on this day. For us, it's the shortest day of the year giving New Mexicans only 9 hours 40 minutes of sunshine.
December 22 (Saturday) Full Cold or Long Nights Moon. The fact that this Full Moon is only one day after the winter solstice make this an especially Long Nights Moon. It will rise at 6:12 PM MST and set the next morning at 8:06 AM. That means this lonely cold moon will be visible for 13 hours 54 minutes! The reason is this full moon is higher in the sky because the sun is at its lowest point for the year and the moon tracks roughly opposite the sun during its full moon phase.
December 25 (Tuesday) Algol at Minimum. The eclipsing binary star Algol will be at minimum brightness at 7:17 PM MST on Christmas Day. You should be able to observe Algol dimming at 6 PM, an hour and 17 minutes before minimum. It will again reach maximum brightness by 10 PM. This may be a good object to look at with that new telescope or binoculars that you received for Christmas!