The Finer Points of Meteor Shower Observing


Want definitions for common meteor terms? See the NAMN Meteor Glossary.

Contents


Where Should I Look in the Sky?

A lot of press releases say that you should face the radiant. You'll also hear advice that you shouldn't face the radiant. I like to keep both the radiant and the zenith in my field of view, but with neither at the center. You should center your field of view high in the sky (>50 degrees elevation) to avoid horizon obstruction. Also, when you have to deal with light pollution or moonlight, keep your field in the darkest part of the sky. Make sure that you are in a comfortable position. I find a reclining lounge chair supplied with pillows and blankets is helpful.


How do I Know if a Meteor Belongs to a Particular Shower?

Meteor observers use three criteria for determining whether a meteor belongs to a particular shower: alignment, relative speed and path length.

Alignment. The meteor's path, when traced backward, points toward the radiant. Here is a trick used by many observers: When a meteor appears, immediately hold a shoestring or other cord up to its path. This makes it easier to visualize where the meteor came from.

Relative speed. Not all meteors aligned with a radiant actually belong to that meteor shower. Each shower's meteoroids have a characteristic speed with which they strike the atmosphere. Orionids and Leonids are fast, at 68 km/s and 70 km/s, respectively. Taurids are rather slow, 30 km/s, and Geminids are only slightly faster at 35 km/s. Relative speed is reflected in the appearance of the meteor, but is difficult for beginners to judge until they have seen a large sample of meteors. Speed is usually noted on a 0 to 5 scale. Orionids and Leonids seen well away from the radiant should rate a 4 or 5; those near the radiant may appear slower due to foreshortening. Also, meteors appear slower when the radiant is near the horizon. But a long, slow meteor that aligns with one of these radiants is unlikely to be an Orionid or Leonid.

Path length. Some illustrations show meteor paths starting right at the radiant and continuing across the sky. This is not correct. Except for "point" meteors seen right at the radiant, there is a distance between the radiant and the starting point of the visible meteor. In fact, this distance is longer than the actual meteor path by a factor of 2 or more. Exceptions are provided by very bright meteors (which become visible higher in the atmosphere and stay visible longer) and by the "earthgrazers" seen when the radiant is near the horizon. In general, just remember that a meteor that becomes visible near the radiant and streaks for a long distance is not a shower member.


Other Sources of Meteors

Around the peak of a major shower, most meteors seen will be shower members. However, a significant number of your sightings will prove to be from other sources. A common term for these is "sporadics" or random meteors. It is fine to identify all non-shower meteors as sporadics, but it is worth noting that there are several minor showers active, as well as patterns in the sporadic activity. See notes included in each shower page.


How do I Collect Useful Data?

While just watching meteors is fun and relaxing, it is possible to gather useful data on major shower activity with simple equipment. For more information, visit the North American Meteor Network or the International Meteor Organization. Both organizations have guides to meteor observing as well as report forms. Here are the essentials:

1. Your data must be that of an individual observer! Do not combine observations or do a group count. Numerous individuals in you party may collect data, but each must submit an independent count.

2. Note the start and end time of your watch, any breaks taken, and any time lost for recording or other purposes. The total duration on the count minus breaks and lost time should be at least one hour.

3. Sky conditions. Each person must determine his/her naked eye limiting magnitude (LM) to +/- 0.1. This should be checked regularly during the count (every 30 minutes, or more often if conditions are variable). If any clouds or other obstructions restrict your view, estimate the percentage of your field they cover. Note the center of your field in Right Ascension and Declination.

4. For each meteor, record the following data:

  1. Shower Association (i.e., "Orionid" or "sporadic")
  2. Magnitude (compare with stars of known brightness)
  3. Relative speed (0 to 5 scale)
  4. Time of appearance to the nearest minute (optional in most cases)
  5. Duration of any persistent train, in seconds
  6. Color, if notable.
I use a portable tape recorder to voice-record these data for later processing.

5. After the count, organize your data into a readable format. Include information on your location: latitude, longitude and elevation.

6. If you wish, you may report your observations to one of the organizations above. I'd be interested to know how your meteor observing experience turns out, so don't be afraid to email me at wes_stone@lycos.com.

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