By Bruce McClure
Friday, Dec. 12
Friday at 14:28 MST, the moon will be closer to Earth than it’s been in the last 15 years. The moon will be less than 357,000 kilometers –– or 222,000 miles –– away. After today, the moon won’t come this close to Earth again for another eight years.
Friday is also the full moon. And the next time the moon comes this close –– on Nov. 14, 2016 –– it’ll be full again.
Extra close moons happen when the full moon coincides with the moon’s closest point to Earth for the month, an event called “perigee” by astronomers. And in case you’re wondering, the moon’s phase does influence its closest distance for each month.
Consider that when a quarter moon happens at perigee – and is closest to Earth –– the moon is at right angles to the Earth and sun –– so that keeps the moon slightly farther away.
But when a full moon coincides with perigee, the sun, Earth and moon make a line in space. The moon’s orbit stretches closer to Earth. So the coincidence of perigee and full moon brings the moon closer to Earth than at any other phase. By the way, the sun’s varying distance also influences the moon’s distance. Because we’re closest to the sun around New Year’s Day, the closest full moon perigees always occur at the beginning or the end of the year.
Will this very close full moon look extra bright? Look outside tonight and see what you think!
Saturday, Dec. 13
The annual Geminid meteor shower is expected to peak tonight.
The Geminids usually rank as one of the best meteor showers for the year in both hemispheres. But this year the nearly full moon will wash out all but the brightest Geminid meteors from view. If you’re a diehard meteor watcher, you can try observing between midnight and dawn. But don’t expect to see many –– if any –– Geminid meteors in 2008.
The Geminid meteor shower will be better next year. This meteor shower gets its name from the constellation Gemini the Twins. If you trace the paths of all the Geminid meteors backward, they appear to radiate from the same point in front of Gemini. This point is called the meteor shower radiant.
Not far from the moon tonight, you’ll see two bright stars close together. They are Castor and Pollux, Gemini’s two brightest stars. In other words, the moon is right on top of the Geminid radiant tonight. Castor, the fainter of these two stars, nearly aligns with the radiant point of the Geminid shower.
Most meteor showers take place when our planet Earth crosses the orbital path of a comet. The comet debris plunges into Earth’s upper atmosphere and the vaporizing particles fill the night with meteors. But the Geminid meteor shower appears to be an oddity. The shower’s parent body looks more like an asteroid rather than a comet.