By Jon Stewart-Taylor
This page is about meteors: what they are and ways to observe them. It's intended mainly for beginning and intermediate astronomers, but in covering the "five 'W's" of meteors:
plus recording observations and some references, i hope it will have something for everyone who enjoys watching these evanescent streaks of light.
Meteors (also known as shooting stars or falling stars) are streaks of light in the night sky. They may be bright or faint, long or short. Meteors are caused by debris (usually particles the size of dust or sand grains left behind by comets) hitting the Earth's atmosphere going very fast. The friction of their passage through the air heats them so hot they glow and ionize the air. Depending on the size and composition of the particles, meteors may be different colors, leave glowing trails, or even explode.
Sporadic meteors (not belonging to any shower) can be seen on any clear night. Depending on how dark your sky is, on a clear night you may see five or so per hour, appearing unpredictably. Comets may have left these particles so long ago that they are now dispersed at random leaving no clear pattern or order.
Besides the sporadic meteors, there are sometimes meteor showers, in which meteors from a lot of debris in the same orbit hits the Earth. Most meteor showers are traceable to particular comets. Meteor showers vary in intensity. Some appear as weak showers barely distinguishable from sporadics, while others appear as (very are) meteor storms in which thousands of meteors are seen per minute.
There is another characteristic of shower meteors which distinguishes them from sporadics. Since all of the meteors in a shower are moving in the same orbit, and hit the earth in a parallel stream. Because of our perspective on Earth, they appear to radiate from a particular point in the sky called the radiant. You may have seen a similar effect driving in a car on a snowy or rainy day. All the flakes (or drops) seem to come from directly in front of you, and fan out to the sides. Although meteors don't always appear to begin at the radiant, if you extend the line of their flight backwards, it will go through the radiant.
There are lots of reasons to observe meteor showers. Little or no equipment is required: just dark skies and something to lie on. Meteor showers are one of the few astronomical events where something actually happens. This helps hold the attention of younger kinds in particular. Meteor shower observing is also one of the places where an amateur astronomer can make real scientific contribution. If you submit your observations to the IMO, they'll become part of the data used to predict future shower performance, and help refine numerical models of the trails of cometary debris in space. Not least, meteors are beautiful, and fun to watch.
Because showers occur when the earth passes through comet leftovers, showers happen occur around the same date every year give or take a day. You can find the predicted dates for the major showers for the upcoming year in the major astronomy magazines, Guy Ottewell's Astronomical Calendar or at the International Meteor Organization (IMO) web pages. Particularly good ones are the Quadrantids in January, Aquarids in May, Perseids in August, Orionids in October, and Geminids in December. Each of these should produce a meteor at least every minute or two. The Leonids (in December) are a mediocre shower most years, but about every 33 years they can produce an astonishing storm with thousands of meteors per minute. Unfortunately for us, the next return is expected around 2032.
Depending on the shower, you may see as many as one every minute or so, or as few as one every 10 to 15 minutes. The number of meteors a shower produces is described using the Zenithial Hourly Rate (ZHR). The ZHR is something of a fiction, in that it's the predicted maximum number of meteors observed in one hour if you have:
ZHRs are usually the maximum expected at the peak. With most showers, the number of meteors drops dramatically a day before or after the peak, with the ZHRs often being only a quarter or less of the peak ZHR. Even at the peak, the number of meteors observed will be lower than the ZHR. This means you should concentrate your observing during the peak, unless you're recording your observations for submission to the IMO.
If you have time (and nowhere to go the next day), you should watch all night. Otherwise choose a time when the radiant is 15-20 degrees above the horizon. For most showers, the best show will be in the hours just before dawn for two reasons. First, for most of the showers the radiant is at its best position just before sunrise. Second, because the Earth rotates from west to east, meteors entering the atmosphere in the morning are at the "leading edge" of the Earth, and their speed relative to the Earth is higher. Meteors in the evening are at the "trailing edge", and their relative speed is lower. In any case, watch for at least an hour. Whenever you plan to start your session, you should arrive at least 20 minutes earlier if you can to allow your eyes to adapt to the darkness.
The ideal site will have a clear view of the horizon in the direction of the radiant. It should be well away from lights, since the darker the sky the more meteors you'll see. Finally, make sure it's a safe area: get permission to use the site if required and make sure there are no hazards. If you get to choose between sites, go for safety first, then dark skies, and finally wide horizons. To determine which horizons are most important, first figure out where the radiant will be in the sky. The name of the shower will normally tell you the constellation the radiant is in. The exception is the Quantrantids, whose radiant is in Bootes. You can use a planisphere, monthly sky chart, or planetarium program to find out where the constellation will be in the sky during the shower. If all else is equal, see if you can get a good Eastern horizon, since for the majority of showers the radiant starts low in the east and moves higher and westward as the night wears on.
Although meteors can be detected with binoculars, telescopes, and cameras, the best way to observe showers is to simply lie back and enjoy the show. As previously mentioned, equipment required for watching meteors is minimal. You should take a reclining lawn chair or a pad like a sleeping bag to lie on. Everything else is optional. Drinks and snacks can help keep you comfortable (and awake). You may want to take a radio or a watch with an alarm so you can figure out what time it is without needing to look. Some paper and a couple of pencils for taking notes can be useful. What you wear during a meteor session depends in part on the time of year. If you plan to be out long it can get quite chilly, even during the summer. The best plan is to bring lots of layers which can be added or subtracted as needed. Dry towels (and a way to keep them dry) are great on nights with heavy dew.
Take your pad or recliner, lay down so you can see the radiant, lay back, and watch. Don't fix your eyes on any one place, not even the radiant. Instead keep them moving around at a comfortable pace in the region between the radiant and the zenith, or 15-20 degrees from the radiant. This will keep you from developing "tunnel vision", which is important because meteors appear all over they sky. You'll catch most of the out of the corner of your eye. Shower meteors tend to appear in bursts. You may watch for ten minutes and see no meteors at all, then see five or ten in the next five minutes. Take a 5 minute break every hour or so. Unless there's an intense meteor storm you won't miss much in 5 minutes, and the break will usually help you see more afterwards.
If you'd like to record your observations there are several methods to try. The simplest is to just write on a piece of paper with a pencil. Write down the time and conditions when you start, and every time you take a break, and then record the meteors as you see them. You can try to write down what you see diary fashion, but i've found that usually takes up to much time i'd rather spend watching. Unless there's a really spectacular meteor (unusually bright, highly colored, or leaves a train), i normally just write a single letter, either "S" for a shower meteor or "N" for a non-shower meteor.
Another method is to use a tape recorder and narrate what you see. This allows you to keep your attention on the sky, but of course you'll have to transcribe the tape later. Remember to put in fresh batteries before you start.
There are also meteor recording programs for computers and hand-helds like the Palm. These have lots of good features, but also have some drawbacks. They are electronics, and probably won't like getting wet if you have a night of heavy dew. You have to be careful about their battery life, especially if you're planning an all-night session. And, to take advantage of most of them you have to take your eyes away from the sky where they belong.
Whichever method you use to record your observations, you may want to submit your data to the IMO or Astronomical League. They have requirements you must meet in order to have your data count, but their web pages describe what they need pretty clearly. For the most part it isn't too difficult. The main thing is to record the observing time and conditions in some detail.
Of course, you may decide you don't want to go to the trouble of recording your observations at all. Pick a good site, lean back, and watch the celestial fireworks.
For more information about meteor showers and meteor observing, you can go to these web pages:
Astronomical
League Meteor Club
International Meteor
Organization
Astronomical
Calendar
Astronomical
Companion
© 2006 Jon Stewart-Taylor