With two camera setups it is possible to photograph the same meteor from two different stations: double-station photography. As is generally known, such a pair of photographs allows to calculate the trajectory of the meteoroid through the atmosphere and its orbit around the sun.
When you want to experiment with double-station photography you will have to select the locations of the two stations and to determine the best point in the atmosphere to aim the cameras at. The following criteria
have to be taken into account:
- The further the meteor is photographed from the radiant, the more accurate its velocity can be determined (with an optimum of 90 degrees distance). Usually, it is best to avoid aiming the camera directly at the radiant of the active shower.
- When you draw great circles through the meteor paths on the celestial sphere, the angle between the two circles is the so-called angle of convergence, or Q. The greater this angle, the more accurate are the results of the calculations. Usually, you want an angle larger than 20 degrees.
General behavior of the angle of convergence
When choosing the locations of the stations the important parameters are the length of the baseline (distance between the stations) and the angle between the baseline and the azimuth of the active radiant. In general the following rules apply: the larger the baseline of the cameras, the larger the average Q.
The larger the angle between the baseline and the azimuth of the radiant, the larger the average Q. So, preferably the cameras should not be lined up with the radiant at any time during the night. When the radiant has an elevation higher than 45 degrees this rule becomes less important.
The first rule has a practical limit of about 200 km, in which case the two cameras have to be pointed in opposite directions towards each other. For camera batteries the practical limit is even as small as 100 km, because for larger distances the overlap in covered areas of atmosphere becomes very small. In general, any baseline larger than 50 km is allright, but smaller baselines may still be useful.
With the above introduction in mind you are ready to start using the tool called QRICHT.EXE (for MS-DOS). This tool requires the following input information:
- start date of the observing campaign
- end date of the observing campaign
- geographic coordinates of 2, 3 or 4 stations
- height in the atmosphere of the aiming point
- geographic coordinates of the aiming point in the atmosphere
You have to enter this information in a file that follows the format of the example file QRICHT.FRM. After that you can enter the command “C:> QRICHT filename”. Then, QRICHT calculates the following figures:
- azimuth and elevation for the camera at each station
- right ascension and declination for the camera at each station at different times
- during the night
- the value of Q for the active streams at different times during the night
So, the tool provides you with all required information to aim your cameras for double-station observations. Only it does not find the geographic coordinates of the optimal aiming point in the atmosphere. You can find this by trial and error, or you can try to apply the general rules and explanation provided in the previous sections. A good value for the height of the aiming point is 100 km. The table below shows more specific values for a few major showers. A distinction is made between photographic observations (typical Lm of +1m) and video observations (typical Lm of +6m).
|Stream||Photographic (km)||Video (km)|
QRicht runs on 16 bit machines. If you are interested in a 32 bit version, please contact Marc de Lignie.