Meteors to light up night skies

Find your way to a patch of dark sky tonight and you are likely to be delighted by one of the year’s most reliable astronomical events.

Earth is encountering the annual Perseid meteor shower, a celestial bombardment of shooting stars and fireballs caused by tiny bits of comet dust being burned as they enter the atmosphere.

Earth’s orbit around the sun takes it through the debris left by the comet Swift-Tuttle each year at this time, but the peak of the show arrives on Aug. 11 or 12.

This year’s peak is forecast to occur at 4 a.m. on Thursday, but viewing earlier in the night should be good as well, said Zeke Zechmeir, president of the Spokane Astronomical Society.

Skywatchers can expect clear skies and mild temperatures, according to the National Weather Service forecast, and a waning moon won’t rise until around 2:30 a.m., ensuring darkness for optimum viewing.

“The Perseids are always a good performer. They are always worth watching,” Zechmeir said.

He recommended getting away from bright city lights and busy commercial areas where the night sky is obscured by glare. Also, choose a place that has an open view of the sky, especially to the northeast.

According to Sky and Telescope Magazine, the Perseid meteor shower is one of the two most dependable meteor showers each year. The Geminid shower in December is the other.

The August event takes its name from the constellation Perseus, which provides the focal point for the shower. The meteors will appear to be coming from an area of the sky next to the constellation. This is known in astronomy as the radiant of the shower.

As with most meteor showers, the best viewing comes after midnight when the radiant rises higher into the sky and Earth’s rotation points viewers into the direction of the planet’s orbit through the comet dust.

Perseus and its neighboring constellation Cassiopeia can be found in the northeast sky. Early in the evening, the radiant is low – but as the radiant rises, the number of meteors could increase to as many as 50 to 60 per hour. Experienced skywatchers know that the radiant becomes apparent after watching for any length of time.

Zechmeir said there is a chance this year’s showers will be more active than during other years because Jupiter’s gravitational pull is allowing Earth to pass closer to the center of the comet trail.

The comet dust is dispersed enough that the showers can be seen off and on between July 17 and Aug. 24, he said.

Sky and Telescope Magazine said the meteoroids in the Perseid stream range in size from pebbles to sand grains. They have a consistency like bits of ash. They ram into our upper atmosphere at a speed of 60 kilometers per hour, creating incandescent trails of light from ionized air.

The best of the meteors look like fireballs and are apparent even if they strike the atmosphere during late dusk or early dawn. The predawn sky is also being graced by Venus in the east.

In addition to this week’s meteor shower, Zechmeir said, an unusually active sun spot could trigger appearances of the northern lights, or aurora borealis, later this week.

Auroras have been reported periodically in the past several weeks as far south as southern Oregon, he said. Some of the best auroras occurred when the current sun spot was pointed toward Earth in July. The sun’s rotation has caused the spot to be facing Earth again this week. Since the moon will be in its crescent phase, viewing of any possible auroras should be good.