13 December 2007

Winter Darkness / Geminids Meteor Shower

The deepening darkness of winter has arrived and with it the beautiful winter skies. The earliest sunset has already passed, but the longest night is yet to come on Friday December 20th when we will experience over 14 hours of twilight and darkness from sunset to sunrise. This date is known as the Winter Solstice and it marks the day when the sun appears to be at its lowest point in the sky (at noon) compared to every other day of the year. From our latitude in San Francisco, this means that the sun will only appear approximately 30 degrees above the southern horizon at noon on December 20th - very low indeed!

December also brings the annual Geminid Meteor Shower. If you spend enough time looking up at the sky on any night of the year you will likely see a few meteors streak across the sky. However, a meteor shower is a special time in which a much higher number of meteors are visible. December 13-15 is a time when the Earth passes through a part of the Solar System which contains a particularly high concentration of dust and particles which enter the atmosphere and burn up, creating the beautiful "shooting stars" that we have come to know. This year the Geminid Meteor Shower comes at a time when moonlight will not interfere with seeing and the weather prospects are good (at least as of the time of this writing). The meteor shower is called the Gemenids because the meteors in the shower all seem to emanate from the same part of the sky in the constellation Gemini.

To see the Geminids, you need to look east in the evening after 9:00 pm, or straight up around midnight, or due west in the pre-dawn skies in the morning. The twin stars of Gemini (Castor and Pollux) are a bright pair and brilliant orange Mars is nearby. These stars and planet mark the spot where the meteors will appear to come from. It's rumored that the early morning hours of Friday 14th should bring some of the finest viewing to us on the west coast. Bundle up in a very warm jacket and hat and take a look. There's no need for a telescope or binoculars. You should see at least a few meteors even in the bright city skies of the Bay Area.