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
