Cold nights bring clear skies

Fri, May 2, 2008

We've had some good clear nights here in West Michigan recently. If the stretch of clear weather continues, there is much to see in the coming weeks.

Early risers should keep their eyes peeled for meteors. If you catch a shooting star in the morning in the next few days, there is a good chance the streak you see is a fleck from Halley's comet.

Twice a year — once in early May and again in mid to late October — Earth orbits through the interplanetary river of debris left behind by the solar system's most notorious comet.

Halley's comet orbits the sun and sails across Earth's own orbit every 76 years. Records of the comet's passage date back to as early as 250 BC. The comet is named after Sir Edmond Halley, the English astronomer who first recognized it swings around the sun periodically.

In 1705, Halley predicted the comet would return to the sky in 1758. His prediction was correct: the comet was again sighted on Christmas Day 1758. Halley didn't live to see the comet that now bears his name; he died in 1742.

Halley's comet last passed by Earth in the winter of 1985-86, but was largely a disappointment for those of us who were excited about the once-in-a-lifetime (for most) chance to see it. It will next be visible in the summer of 2061.

But Halley's comet sheds bits and pieces as it orbits, and these we can see each year as shooting stars. The meteor shower in May, which is attributed to Halley's comet, is called the Eta Aquarids — Aquarids, because Aquarius is the constellation the shooting stars seem to shoot from.

On Tuesday, May 6, when the meteor shower is predicted to peak, Aquarius is above the horizon in the early morning hours. This year, the conditions for viewing the Eta Aquarids are about as good as they get here in the Northern Hemisphere because the moon is new, which leaves the sky as dark as possible, that very night. You can expect to see about 10 meteors per hour if you set out to observe enthusiastically.

Evening-oriented skywatchers should keep their eyes out for Mercury over the next couple of weeks. This week, look for the closest planet to the sun near the Pleiades — a small cluster of stars that looks like a tiny Little Dipper — just above the western horizon in the darkening sky after sunset.

The sun sets tonight at 8:49 and Mercury sets about 90 minutes later. Head to the shoreline and bring a snack.

After Mercury sinks below the horizon you can set your sights on Mars and Saturn. Both planets are high in the sky after sunset, with Mars slipping to the east of Gemini and Saturn standing grand in Leo.

And for you night owls, watch for Jupiter to rise in the east around 2 a.m.

Although the recent cold snap seems to have set our summer plans back a few weeks, the cold usually brings clear skies. Actually, it is the other way around. When the sky is clear, the ground and air near Earth's surface radiate away into space the heat accumulated during the day.

So take the good with the bad and get out in the cold for a nice look at the starry sky.

Doug Furton is a member of the physics faculty at GVSU. Send questions and suggestions to dgf@inbox.com. An archive of his "What's Up" columns is available online at http://gegenschein.wordpress.com.