Comet Halley Chaff Sparks Weekend Eta Aquarid Meteor Shower

Watch for the Eta Aquarid shower this week, so called because meteors will appear to radiate from a radiant near the star Eta Aquarii. The meteors are spawned from fragments of Halley’s Comet strewn about its orbit. Every May, Earth crosses the stream and we get a meteor shower. At maximum on Saturday morning May 6, 25-30 meteors per hour might be seen from the right location under dark skies. Map: Bob King, Source: Stellarium

It’s back! The annual Eta Aquarid meteor shower reaches maximum Saturday morning (May 6) in the hour or two before the start of dawn. That means getting up to look around 3-3:30 a.m. for the best view. An ungodly time to be sure, but since it’s Saturday, we can make it up by sleeping in.

A long-trailed, earthgrazing Eta Aquarid meteor crosses a display of northern lights on May 6, 2013. Earthgrazers, meteoroids that skim the atmosphere and last for several seconds, are more commonly seen when a meteor shower’s radiant is low in the sky or even below the horizon. Credit: Bob King

Rates for this annual shower are typically 25-30 meteors an hour for skywatchers living in tropical latitudes, where the radiant stands fairly high up in the eastern sky. For those of us living in mid-latitudes, we’ll see closer to half that number or roughly a dozen per hour. That’s because the radiant or point in the sky from which the meteors will appear to radiate, will be low in the southeastern sky. Meteors shooting upward from the radiant will be visible, but those some distance below the radiant will be cut off by the horizon.

Each year from mid-April through late May, Earth crosses the orbit of Halley’s Comet and plows through the trail of rocky debris boiled off the comet by the sun. Bits of rock about the size of Grape Nuts strike the upper atmosphere at the fantastic speed of 148,000 mph (238,000 km/hr) and vaporize to create swift, short-lived streaks of light called meteors.

A meteor radiant mimics the vanishing point where railroad tracks appear to touch in the distance. Naturally, they don’t — the tracks remain parallel. Credit: Jakec/ CC-BY-SA4.0

They appear to stream from the radiant, but this is merely a perspective effect.  The same way that parallel railroad tracks appear to come to a point in the far distance, the paths of each Grape Nut striking the atmosphere are all parallel to one another and appear to converge or come to a point in the sky. On Earth, we call that spot the vanishing point; with meteor showers, it’s named the radiant.

Sporadic meteors, those not associated with a meteor shower, spark the sky at the rate 5-7 per hour and are visible every night of the year. You’ll be able to tell an Eta Aquariid from a sporadic by tracing its path backwards. If it points toward the southeast, you’ve just seen a bit of Comet Halley go up in flames! Of course, meteors don’t produce flames despite appearances. What we see is a glowing tube of ionized gas, much the way the neon gas glows in a restaurant sign. Meteoroids — the name given to meteor bits before they burn up — are traveling so fast, they excite the atoms composing the air, which then release light when they calm back down. That light is the bright streak or meteor.

The Eta Aquarid shower is long-lasting with a slow rise in activity starting in mid-April, peaking around May 6 and falling off at the end of the month. That means tomorrow morning will be nearly as good for meteor watching as Saturday. Sunday would too if it weren’t for the return of the bright gibbous moon to the morning sky. Moonlight brightens the sky and reduces the number of meteors visible.

There will be some moonlight early on Saturday, but it sets shortly before twilight begins. Plan to be set up and watching by 3 if you live in the northern U.S. (that gives you a solid hour before the start of dawn) or 3:30 if you live in the southern U.S.

This is what skywatchers with access to dark skies will see while facing southeast in the direction of the Eta Aquarid meteor shower this week. The summer sky’s in full swing at that hour. Created with Stellarium

For the best view, find a location as far from city lights as is convenient for you with an open view to the east or south. I like to use a reclining lawn chair and stay warm and cozy under a sleeping bag or wool blanket. Face toward the east or south and … just watch. While waiting for your first or next meteor, look around the sky. At that hour, the summer stars have firm control of the night. Sagittarius and the planet Saturn shine due south (2-3 fists high depending on your latitude) with the band of the Milky Way prominent across the southeastern sky. The Summer Triangle’s there, too, and if you stay up till 4:30, shiny Venus accompanies the start of dawn low in the eastern sky.

The International Space Station is currently making passes in the morning hours from many locations. Check Heavens Above or Spaceweather’s Satellite Flybys for times and directions for your location. One could do worse than lose a little sleep over such heavenly sights.