After sunset on Sunday December 13th look toward the east or west for ‘shooting stars’, or meteors. Toward the east the short-lived streaks of light are radiating outward from the area of the Gemini Twins constellation. These are the annual Geminids – one of the best meteor showers each year, and at times rivaling the August Perseids. The Geminid Meteor Shower is named for the constellation that the meteors radiate outward from. This is the same for all meteor showers, and the ‘spot’ in the sky is known as the radiant. The Geminid radiant, as shown in the graphic, is just above the ‘twin’ star Castor, and under ideal viewing conditions an average of about 70 meteors per hour could possibly be seen. This year without the interference of moonlight will increase the chances of seeing the meteors.
Meteor showers result from the Earth’s orbital path intersecting areas of comet debris. Comets, as they orbit the Sun, leave behind pieces of their icy, dirty, selves. If these debris clouds happen to be along the Earth’s orbital path then the Earth will regularly pass through the comet debris cloud. As this happens the small comet pieces hit our outer atmosphere and vaporize from the friction generated heat. We then see these as the shooting stars that make up meteor showers.
There are, however, two exceptions to this. The January Quadrantid Meteors and the Geminids each come from their own respective asteroid rather than a comet. The source for the Geminids is Asteroid 3200 Phaethon
Looking toward the south to southwest and adding to viewing the Geminids is an un-named meteor shower with a radiant just below the bottom of the ‘Square of Pegasus’, between the ‘square’ and the ‘Circlet’ pattern of stars forming the head of the Western Fish of Pisces the Fishes. This meteor shower originates from Comet Wirtanen, a short-period comet orbiting the Sun every 5.5 years. The comet was discovered in 1948 and according to some predictions the Earth may pass through this comet’s debris cloud for the first time since the comet’s discovery. This part of the sky is over the south at sunset and as this graphic shows the radiant is over the southwest as the Geminids radiant is over the eastern horizon.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.