If the weather is clear Wednesday night next week, our skies are likely to fill with the greatest number of visible shooting stars we’ve had in quite a few years.
The big occasion is the U.S. getting perfect astronomical conditions for the strong Geminid meteor shower.
What if it’s cloudy on the big night of the Geminids, Dec. 13-14? We may still see some of these meteors on neighboring nights, in addition to viewing several beautiful pairings of the crescent moon with the planets Jupiter and Mars.
What causes meteor showers?
Every year on about the same dates, Earth passes through swarms of rocky particles associated with the orbits of various comets. When these meteoroids encounter Earth’s atmosphere at tremendously high speeds — up to far more than 100,000 mph — they burn up from the friction and produce the brief streaks of light we call meteors.
A meteor shower is not just an increased number of meteors, however. It is the meteors from a particular swarm all appearing to shoot out from a particular point among the constellations, a point called the radiant. In the case of the Geminids, the paths of the meteors all appear to point back to the famous zodiac constellation Gemini the Twins. Gemini is now rising about sunset and is already high by midevening, so, unlike any other major meteor shower, the Geminids can be seen in good numbers by as early as 9 or 10 p.m.
Why is this year so favorable for the Geminids?
In some years, the moon is at a large phase all or most of the night and its bright light washes out our view of most of the meteors. This year on the big night, the moon doesn’t rise until about 3:30 a.m. — and is even then only a slender crescent — with 10 percent of the moon illuminated — so it doesn’t really bother our view of the Geminids.
The other reason why this year is astronomically favorable for the U.S. to see the Geminids is the exact timing of Earth’s encounter with the central section of the meteoroid swarm. The Geminid shower produces near-peak numbers for about 24 hours, so even the night before the maximum of the shower could give us pretty good numbers of meteors. But the climax of the shower this year is predicted to occur about 1 a.m. Dec. 14 — which is only one hour before the radiant in Gemini is highest for observers in the eastern U.S. So next week, Wednesday evening to Thursday dawn, should provide the very best numbers.
How many meteors will you see?
The last year that there were similarly favorable conditions for the Geminids I saw 68 of them in my best hour, along with about 14 meteors from other directions. Within the light pollution of a fair-sized city on the big night, you might only see a maximum of 10 or 15 Geminids per hour. But some of them will be bright meteors, maybe a few brighter than any star or planet, or even as bright as the moon. Geminids come in all colors, sometimes have boisterous flaring, bursting flights, and sometimes leave lingering, luminous trails.
A timetable for Geminid watchers
In the early evening, about 5:30 to 7 p.m., the radiant in Gemini is still low, so not that many meteors will be visible. The few Geminids that do occur then, however, will tend to be “earthgrazers” — meteors with incredibly long flights, sometimes almost all the way across the sky. By 9 or 10 p.m. the numbers could be up to four dozen or more per hour. From 11 p.m. to 4 a.m. Geminid rates of 60 or more would be possible if skies are quite clear.
A bonus of moon and planets
An hour or so before sunrise on Dec. 13, the crescent moon is just above the currently dim planet Mars, with Jupiter well to the lower left. But at the same time the next day the moon is dramatically close to the upper right of bright Jupiter.
Fred Schaaf is a local author and astronomer. He can be reached at: firstname.lastname@example.org.