With no moonlight to interfere, this should be the best night for stargazers to get a look at the annual Orionid meteor shower. Forecasters are calling for "mostly clear" skies tonight, with calm winds and lows in the 40s.

Observers say Orionid activity has been picking up in recent days, with a strong showing in some places, and several bright fireballs. This same shower last year produced an impressive fireball seen from Elkridge. The photo above was taken early today by Jefferson Teng, in Shanghai, China. (Used with permission.) You can easily see the constellation Orion in the top center of the photo.

"I woke up early in the morning to observe the shower through my bedroom window," says Teng. "This one was quite bright considering the light pollution in Shanghai."

This shower is active from early October through early November. The meteors arrive as the Earth, making its annual trek around the sun, passes through the dusty trail of Halley's Comet, which last passed through the inner solar system in 1986. Like bugs on the windshield, the comet dust strikes the atmosphere at high speed, heating the air as the grains streak in, causing it to glow. About half will produce persistent trails.

Here is a gallery of a few of the first 2009 Orionid meteor photos. Here is the 2006 gallery.

The Orionids average around two dozen an hour under dark-sky conditions. But since 2006, observers report the shower has produced counts of up to 60 an hour. The people who calculate these things say the increased activity is occurring because the Earth happens to be passing through several old streams of Halley's dust, left behind during some of the comet's early periodic passes through this part of the solar system - specifically, during its appearances in 1266 BC, 1198 BC and 911 BC. 

We passed through the same region in 2006, 2007 and 2008, with plenty of meteors, and this year is expected to be similar.

The best time to look is after the constellation Orion (Left, NASA sky map) rises in the east, around 11 p.m. But if you can manage it, the most promising hours are those before dawn. If you miss the show tonight, try again on Thursday morning. Friday looks like it will be cloudy or rainy.

The meteors will appear to emerge from Orion, but may appear anywhere in the sky, so find a dark spot with a good view in all directions. Dress for the cold. A lounge chair and a warm sleeping bag will make things a bit more pleasant.