QRICHT description
A more extensive version of this description was published
in the 1996 December issue of WGN.
Introduction
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.
Computer program
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 |
Video |
| (km) | (km) |
| Quadrantids | 89 | 96 |
| Lyrids | 94 | 101 |
| Perseids | 96 | 104 |
| Orionids | 99 | 107 |
| Leonids | 102 | 108 |
Marc de Lignie;
last change: November 20, 1996