Observations during exceptionally high activity
If the activity of a shower is so high that it becomes simply impossible to count all the meteors seen, we refer to this event as being a meteor storm. Most people can count themselves exceptionally fortunate to witness one such spectacle in their lifetime, but occasionally some observers have been still luckier and seen two or more. A meteor storm is an incredibly impressive phenomenon to view in its own right, but besides enjoying the show, with a little forward-planning you can also record valuable data for later scientific analysis.
With an increasing meteor rate, the main problem with trying to record the activity using the standard counting method is that the time available for recording the data for each meteor is greatly reduced. This leads to a probable loss of data, and so as more meteors appear, information recording should be restricted to the most important data only. The most vital information about a visually observed meteor is its brightness. When activity is very high, determining shower association is much less important, as only a very small fraction of the meteors seen will not belong to the shower. To achieve maximum recording speed, you should just speak the magnitudes (estimated only to the nearest whole magnitude) onto tape. If there is an obvious sporadic then add this information. All other magnitudes can be assumed to belong to shower meteors. Do not forget to put enough time labels into your tape recording. Here, time labels should be given every 5 or 10 minutes. The importance of having the magnitude for each meteor recorded cannot be stressed too highly. Simple counts made without estimating the magnitudes are almost completely useless for analyses (cf. Koschack, 1992; Koschack et al., 1993).
If you feel that meteor rates are so high it is becoming impossible to record the magnitudes for all the meteors seen, record only the magnitudes of those of +4mag and brighter. Simply ignore the fainter meteors. If even this becomes impractical you should restrict yourself to recording only events of +2mag or 0mag and brighter, as seems most suitable. When the activity decreases, you should reverse this process. Whenever you switch to another minimum magnitude insert a time label with a remark like “<=+4” in your record.
If the limiting magnitude is better than ~+5.0mag and you are also carrying out the photographic observations outlined in the following subsection, you can stop your visual observation at the point when it becomes impossible to record all meteor magnitudes of +4 mag and brighter. Then you can fully concentrate on the photographic program and enjoy the show. It would be very useful to record the appearance time for any bright fireballs and also try to estimate the time of maximum activity. For limiting magnitudes worse than ~+5.0mag this is recommended from the moment when you would have to switch to 0mag and brighter meteors.
As soon as possible after the event, you should report the complete record of your observation (i.e. the meteor list with time labels, start, end and break times, and information about clouds and limiting magnitude) to the VMDB input officer. Also enclose a short report including the estimated time of the maximum, remarkable events like bright fireballs, any special circumstances, remarkable properties of the meteors (e.g. persistent trains), etc. This reporting procedure should only be used when the activity was extraordinarily high (observed rate greater than about 500).
Peaks of meteor shower activity
The climax of observing a major shower is its maximum. During these times the counting method is the only appropriate way to record the activity. Maxima with a rate of 100 observed meteors per hour are well within the limits of this method. If the meteor shower becomes so strong that you do not feel able to record all the data anymore, you should leave out some of the information per meteor. Details like color and persistent train can be omitted first. The magnitude of the meteor should not be missed but it is sufficient to estimate whole magnitudes only. You can leave out indicating major shower meteors and only denote meteors which do not belong to the major shower by “S”. In this way an observer can manage to record around 200 meteors per hour.
High activity is the only case in which we can break up the observation into intervals shorter than 1 hour. The interval length depends on the number of meteors seen. In order to study the small-scale structure of the stream we can even break up the magnitude distribution into two or three per night.
- Give time labels every 10-15 minutes in your observation record.
- Intervals for rate calculations should contain about 20 to 30 meteors.
- Give the numbers of shower and non-shower meteors only.
- Magnitude distributions should contain 40 to 60 meteors.
- Estimate meteor brightnesses as integers.
Finally, we have to be prepared for even higher activity. If we are not, we may lose much valuable data for such extremely rare events. The following section gives some advice on how to observe this meteor spectacle.
The MetSim software
The Leonid returns between 1998 and 2003 were a challenge to visual meteor observers. In fact, it was quite difficult to obtain reliable activity data from visual counts because of the exceptional high rates. A calibration of the data by imitating the conditions during the maximum could provide us with more reliable ZHRs. One method to do this is simply “estimate the number of meteors visible when looking at the sky for one second”.