Observing a Meteor

When a meteor appears keep a cool head. Try to store the phenomenon as a whole in your memory. Then keep looking at the sky in order to memorize the following data (in this order):

1. The path
   

   The most important information is its direction rather than the exact start/end points. Memorize it corresponding to the background stars, e.g. in between which stars the meteor passed or to which ones it can be traced back or prolonged.

2. Maximum magnitude
   

   Estimate this by comparing it to the brightness of the nearby stars you memorized at the beginning of the watch.

3. Angular velocity
   

   In order to have a quantity that can be compared to an expected value for shower association you should estimate this in degrees per second. This is not difficult. In your imagination you make the meteor move for one second. The time span of one second can be easily reproduced and the sensation of the angular velocity you have still in your memory. The path length in degrees the meteor would have reached after moving for one second is its angular velocity in degrees per second. Once you have some experience you will have the scale fixed in your memory and can then estimate the angular velocity directly without this procedure.

   Do not try to estimate the duration and to obtain the angular velocity by dividing the path length by the duration. The duration is very difficult and uncertain to estimate and the path length is affected by plotting errors, thus the resulting uncertainty in the angular velocity is much greater than if you convert the sensation of the velocity directly into degrees per second. The figure below gives you an idea about the accuracy experienced observers achieve.

   
4. Persistent train
   

   Give its duration in seconds. Very short trains, the so-called wakes, may be simply marked with a "+". Long-duration trains of bright meteors can show interesting behaviors of decay. They might become bended or distorted, and you should note details on these phenomena.

5. Color
   

   Note that it is generally impossible to detect colors for meteors fainter than magnitude +2. This information is of least value of all the data.

Now you can switch on your dim red torch and choose the chart the meteor is best plotted on, i.e. that chart for which the meteor occurs nearest the center. It is worthwhile preparing your stock of charts such that you know the sequence exactly and you may find the most suitable chart without interruption of the observation, needing to look at the paper only then. The next step is the identification of the stars you used for memorizing the path on the chart. Since the charts contain all stars down to magnitude +6.5mag you should readily find them on the chart unless your limiting magnitude is considerably better than +6.5mag. This step is one source of plotting errors, therefore be careful! If you are sure that you have found the right stars you can plot the meteor from memory. For identification the plot must be numbered.

Finally, you should estimate the accuracy of the plot with the following scale:

1. very accuratey
2. medium accuracy
3. poor accuracy

For your first observations, plotting will require some time. Do not hurry: take the time to plot carefully. Quality is most important! The time needed for plotting will reduce rapidly with your increasing experience. Experienced observers need on average 10 to 30s.

After plotting, look at your watch to record the time. Unless you saw a fireball the time needs to be a rough estimation only. An accuracy of 1 minute is sufficient. Then the remaining data should be recorded. You can complete a list as shown below.

In order to save some observing time you can record the data on tape. In this case you should fill in the list after the observation. For plotting meteors you will need a certain amount of time, during which you look at your chart rather than at the sky. Therefore, the effective observing time must be reduced by the plotting time. It would be a major effort to record the time you used for plotting every individual meteor, so it is better to determine an average time for plotting one meteor as outlined below.

Use a stopwatch that is able to add times. When you start looking at the chart start the stopwatch, when you resume looking at the sky stop it. (For example, start the stopwatch for plotting, stop after the plot is done at, say 38.4 s (0:38.4), when the next meteor occurs after some minutes start again at 38.4 s, stop after the plot at 1:22.6, and so on). After observing a number of meteors, say 25, the stopwatch displays the time you did not observe the sky, say 16 min 40 s. Dividing this time by 25 meteors you obtain an average plotting time of 40 s per meteor (16 min 40 s = 1000 s, 1000 s / 25 meteors = 40 s / meteor). If you observed, for example 29 meteors in an interval, the total plotting time to be subtracted from the effective time is 29 meteors times 40 s/meteor = 1160 s = 19 m 20 s ~ 19 min. On the report form (interval analysis) these quantities have to be filled in on the line: "Time for plotting _______ s / meteor, _______ min total". For experienced observers the average time for plotting a meteor is a constant that should be checked about twice a year by the procedure described above. Beginners should check it regularly, say every third meteor watch.