Keep an eye out for Saturn and Jupiter this week, which are closing in on one another in the southwestern sky after sunset, on their way to a “Great Conjunction” on December 21. Between December 12 and December 29, the two planets will be less than one degree apart, allowing them to be viewed together in the eyepiece of backyard telescopes. Also, on the nights surrounding December 13, the two planets pass only a degree north of the magnitude 9.9 globular star cluster Messier 75.
Tuesday, December 8 – Last Quarter Moon (at 0:37 GMT)
When it reaches its last quarter phase at 0:37 GMT on Tuesday, December 8 (or 7:37 p.m. EST on Monday, December 7), the Moon will rise at about midnight, and then remain visible in the southern sky all morning. At last quarter, the Moon is illuminated on its western side, towards the pre-dawn Sun. Last quarter moons are positioned ahead of the Earth in our trip around the Sun. About 3.5 hours later, Earth will occupy that same location in space. The week of moonless evening skies that follow last quarter will be ideal for observing deep sky targets.
Saturday, December 12 – Old Moon near Venus (pre-dawn)
In the southeastern pre-dawn sky on Saturday, December 12, the delicate sliver of the old crescent Moon will be positioned several finger widths to the upper right (or 4.5 degrees to the celestial west) of bright Venus. The Moon and Venus will fit together within the field of binoculars (red circle). For several hours following sunrise, sharp eyes can look for Venus’ bright point of light shining a short distance to the left of the moon in daylight. At approximately 22:00 GMT on December 12, the Moon will occult Venus for observers in easternmost Russia, Hawaii and western North America.
Monday, December 14 – Geminids Meteor Shower Peak (midnight to dawn)
The Geminids meteor shower, usually one of the most spectacular showers of the year, runs from December 4 to 17 annually. In 2020, the shower will peak before dawn on Monday, December 14. Geminids meteors are often bright, intensely coloured, and slower moving than average because they are produced by particles dropped by an asteroid designated 3200 Phaethon. The best time to watch for Geminids will be from full darkness on Sunday until dawn on Monday morning. At about 2 a.m. local time, the sky overhead will be pointed toward the densest part of the debris field, and up to 120 meteors per hour are possible under dark sky conditions. True Geminids will appear to radiate from a position in the sky above the bright stars Castor and Pollux, but the meteors can appear anywhere in the sky. A new moon on the peak night should deliver a terrific shower for 2020.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.