Living Columns & Blogs

December chill greets meteor observers and splendid pairing of crescent moon, Venus

Autumn fog has blanketed the Mid-Columbia. Morning frost covers car windows and dried amber leaves tumble from their summer perches like swallows darting after unseen prey.

For the next few months, pockets of cold, heavy air will sweep across the Cascades Mountains and stretch down from Canada to fill the lowlands of southeastern Washington. There it stagnates between basalt-hardened ridges to create blankets of drizzle — gray clouds separating us from the blue skies and stars overhead.

Stargazing is challenging during the winter. Records reveal that during December an average of only eight days are clear or partly clear. This is compared with a more welcome 27 clear or partly clear days in July. January holds even fewer clear days. Little wonder we take joy in celebrating winter holidays.

But when a new weather front stirs the lower atmosphere, the warmth of sunshine again enters our windows and the bright stars of winter constellations invite night time observers to step outdoors.

Notice how far south the sun is now rising, setting, and crossing the noon-time sky compared with summer days. Long shadows stretch across the ground signaling that winter is at hand.

What causes winter to blanket the Northern Hemisphere? Contrary to popular belief, it’s not our planet’s distance from the sun. The Earth orbits closer, in fact 3 million miles closer, to the sun during January (92 million miles) than in July (95 million miles). Rather, our seasons are linked to our planet’s tilt.

The North Pole leans away from the sun during the Northern Hemisphere’s winter and toward the sun during our summer. This tilt causes the winter sun to hug the southern sky, shadows to lengthen, cold air to slide south and daylight hours to shorten.

Remember that when we bundle up, people living in the Southern Hemisphere are enjoying summer. Why? The Earth’s South Pole is now leaning toward the sun — delivering more sun energy to warm the atmosphere, oceans and land south of the equator.

During December, two easily seen celestial events are drawing attention. These include a close pairing of the moon and Venus plus a splendid winter meteor shower.

Perhaps the best description of Dec. 7’s close visual encounter of the crescent moon and Venus is to imagine a celestial jeweler patiently setting a dazzling diamond (Venus) onto a ring formed by the dimly illuminated circle of the waning moon.

On Dec. 7, the moon rises in our eastern sky about 3:30 a.m. Ten minutes later, Venus rises from the same spot.

With each passing minute, the moon nudges closer to Venus as they rise because of the Earth’s unceasing eastward rotation.

By 4 a.m., the moon’s thinly lit side will be visible about three lunar-widths from Venus. One hour later, that distance shrinks to two-lunar widths. And by 6 a.m., our moon and sister planet are just one lunar-width apart. A stunningly beautiful sight.

Likely the most favorable time to observe is before 6 a.m., when both objects rest high in the eastern sky and are set against pre-dawn darkness.

The moon does cover (occult) Venus at 8 a.m. However this takes place after sunrise and will not be easily visible to the unaided eye.

One week later, the Geminid meteor shower highlights nighttime observing. Next to the Perseid meteors of August, the Geminids are the brightest, most consistent, and most active meteor shower of the year. Dark, clear skies will enable viewers to sight one to two meteors a minute.

This shower is named after the winter constellation of Gemini from where the meteors radiate.

The best times to observe are from 9 p.m. to midnight Dec. 13 and 14. This is when the shower’s radiant rests nearly overhead. Hard core observers can also count numerous meteors between midnight and dawn.

Over the years, I’ve enjoyed watching the Geminids because it is sometimes rich in yellow tinted fireballs moving much slower across the sky than the speedy Perseids of summer.

Most meteor showers originate from small pieces of comets. However, the parent of Geminid meteors is a rocky asteroid named 3200 Phaethon. This asteroid orbits the sun every 1.4 years, and therefore frequently replenishes future meteor forming debris.

If you’re venturing outside this month to watch the night sky, pay attention to the weather reports, dress warm, and treat yourself to hot drinks. A recliner will add to your observing enjoyment.

Roy Gephart is a retired environmental scientist and an avid amateur astronomer. He can be reached at roygephart@yahoo.com.

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