Early Bird Gets the Eta Aquarid Meteor Shower

We've got a little meteor shower happening this weekend. The annual Eta Aquarids will peak on Sunday morning May 5, but if the weather's poor you'll still see a few on Saturday and Monday mornings, May 4 and 6. Halley's Comet is responsible for the shower which produces up to 40 meteors per hour for observers in the tropics and southern hemisphere.

For those of us living at mid-northern latitudes, that number will be somewhere between 10 and 20. That's because the radiant, the point in the sky the meteors shoot out of, doesn't rise until around 2 a.m. local time — only an hour or two before the start of morning twilight. During any shower, the higher the radiant rises the more meteors you'll see. Since the Eta Aquarid radiant sits low for northern hemisphere skywatchers, we see fewer meteors.

Twilight is also a factor. The farther north you live, the sooner dawn begins, further cutting into meteor-watching time. I live in the northern U.S. where the radiant stands just a fist high in the southeast at the start of dawn. Yet several years back the shower proved a pleasant surprise. Although I didn't bag gobs of meteors — I remember fewer than a dozen — they shot across the sky with great speed, making for an exciting morning.

Some were bright and left persistent trains, glowing streaks of ionized air that linger for a second or two after the meteor is extinguished. I saw activity well into twilight.

This year we're lucky to have no moon to mar the shower. In fact, this may be the best meteor show of the year. The August Perseids and December Geminids are richer but they'll both be severely compromised by full moons.

You'll have to get up early to see the Eta Aquarids, but on the up side, your time investment need only be about an hour. Twilight length varies according to latitude, lasting from about 2 hours for the northern U.S. and central Europe to an hour 35 minutes for the southern U.S. and 75 minutes in the tropics. For most of us, 3 to 4:30 a.m. should be ideal, but if you want to refine the time to your location, click here for your local sunrise, then back off about 3 hours to find the time for good viewing in dark skies.

No matter how you cut it, it's early. But there is another way to see a few Eta Aquarids without losing sleep. You can watch for earthgrazing meteors the night before the peak even before the radiant rises. Earthgrazers are long-lasting meteors that rise up from the direction of the radiant (east) and flare for several seconds or longer as they skim the top of the atmosphere. I've seen a few, and each has been memorable. Watch for them late Saturday night into Sunday morning.

I mentioned Halley's Comet early on. Most meteors originate from debris lost by comets when they pass near the sun. Solar heating vaporizes dirty ice, leaving dust and small rocks in the comet's trail. If Earth happens to pass through that trail, we slam into the material at high speed and it flares as as meteors. Since cometary material is small, the heat of entry incinerates the particles. We know of no meteorites from meteor showers.

We cross Halley's path twice a year — in early May and late October. In May, Halley-stuff streams from Aquarius and in October, from Orion as the Orionid meteor shower. The comet won't return until 2061 so enjoy this yearly remembrance.