Advanced Meteor Observing
It's fun to record what you see.
It's a lot more fun, however, to record what you see in a scientific manner so you can join in the worldwide observing campaigns of the International Meteor Organization (IMO). Meteor studies have relied heavily on amateur observers for more than a century. They still do.
Many efforts in the past, however, floundered because of one big problem: the observers didn't acquire their data in a consistent way that made it useful. The number of meteors you see depends heavily on the amount of light pollution at your site, the altitude of the shower's radiant, the size of your unobstructed view, and other factors. These variables need to be recorded and controlled as well as possible, so that corrections can be applied to make everyone's counts intercomparable.
Since its founding in Belgium in 1988, the IMO has done an excellent job of standardizing this formerly disorganized field worldwide. Amateurs now have a professional-quality organization to set guidelines for observers, receive their data, reduce it, analyze it, and publish it rapidly.
The true measure of a meteor shower's intensity the standard to which every observer's count is reduced is the zenithal hourly rate, or ZHR. This is the number of meteors that a single observer would see per hour if the shower's radiant were at the zenith and the sky were dark enough for 6.5-magnitude stars to be visible to the naked eye.
A successful meteor campaign results in a "shower profile," a graph of ZHR versus time. If enough observers spaced around the globe can keep the shower under 24-hour watch for many days running, a full record can be made of all its activity. This in turn provides a cross-section of the meteoroid swarm in space invaluable for studies of these closest, yet best hidden, pieces of the solar system.
But to create a good shower profile, one with small error bars, thousands or even tens of thousands of meteor observations are needed. So everyone who turns out and uses the methods described on the following pages will be filling a real need.
Where, When, and How to Watch
Generally plan to start your meteor watch after midnight. That's when the night side of Earth faces in the direction in which it's moving around the Sun. The forward-facing side of Earth (after midnight) sweeps up more meteors than the trailing (before midnight) side.
You don't need much gear. Bring a watch and a dim, red-filtered flashlight to read it by. You can make notes with a clipboard and pencil, but much better is a tape recorder with a microphone switch. This way you can dictate notes in the dark without taking your eyes off the sky. Cold-weather observers should keep the tape recorder inside their coat so it doesn't freeze up. Meteor vigils can get surprisingly cold, so it's wise to dress for the iciest depths of winter.
Bring a reclining lawn chair to a good, dark site with an open view of the sky. No trees or buildings should intrude into your view except maybe at the very edges. If you came from a brightly lit house, give your eyes at least 15 minutes to adjust to the dark. Settle in, look up, and relax. When you're ready to begin watching steadily, note the time to the nearest minute.
The simplest project is just to count the number of shower and non-shower meteors that you see. Watch the sky at least 50° up, and pick a direction away from the shower's radiant point. Keep your field of vision filled with sky. If obstructions do intrude they should block no more than 20 percent of your view, and you need to note the percent they cover. The same applies to clouds. Note the time whenever the amount of cloud obstruction changes, and if the total increases to more than 20 percent, take a break. When your data are reduced, an adjustment will be made for the fraction of your view that was blocked.
Once in a while a meteor will catch your eye. If its path, extended far enough backward, would cross the radiant point of the shower, note it as a shower meteor ("P" for Perseid, "L" for Leonid, and so on). You can note all other meteors simply as non-shower meteors (for example, "NP").