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The useful planisphere for Meteorobservers and
You can adjust this Planisphere in the following way. On the upper transparent disk is a timescale. Find the actual time on this disk, and align this with the actual date(that can be found on the lower disk) by rotating the upper transparent disk. The stars that are witkin the oval on the upper disk can be seen in the actual sky (hold the map above your head with the N to the North). The local star time can be found at the bottom of the disk. The vertical line there points to the actual star time. The curved lines are the altitude and azimuth lines. For example, on december 1st at 24 hour the star Betelgeuze (alpha Orionis) has an azimuth of 142 degrees and an altitude of 40 degrees. The outer scale on the lower disk provides the right ascension (alpha), in the line from the center of the map outwards the declination (delta). This map has special features for the meteor observer. In the first place all radints with a ZHR of more then 5 meteors per hour are market with an R and a number, wich corresponds with the shower shower concerned in table 1on the back of the map. The drift of the shower during its activity is marked with small crosses. Secondly, this map provides a method for calculating the limiting magnitude. On the front of the map you will find 20 number and shaded areas. If one counts all the stars visible witkin this area(count the corner stars as well) you can look up the limiting magnitude in table 2. Look for the row with the number of the selected area.
Observing meteors is fun, but it is also useful. By counting the number of meteors you see in a known period, you can abtain the activity of a shower. Of every meteor you see, you note the originating shower and the brightness in magnitudes. Ideally, this should be done in periods of one our. The length of each interruption in the observation period must be carefully noted down. Obtain the limiting magnitude each quarter of an hour. In addition to every bright meteor you see, you can note the altitude, azimuth and other special remarks on your observation form.
The activity of a shower is measured as the Zenithal Hourly Rate (ZHR).
That is the number of meteors you can see per hour under perfect conditions,
when the radiant is directly above you.
Corrections are made for the limiting magnitude, the altitude of the radiant and the percentage of the sky you cannot see due the clouds. You can compute the ZHR yourself with the following formula:
where number stands for the number of shooting stars you saw in a known period, Teff is the time in minutes elapsed between the start and end of the observation minus the time it toke to note them down, k is the percentage of the sky that was obstructed by clouds, Lm is the limiting magnitude, r is the population index (see table 1) and h is the altitude of the radiant which can be found on the map.