Red Barn Observatory MPC/IAU H68

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A Practical Guide To Chasing Asteroids

For The Astrometrist

By: Steve E. Farmer Jr. & Marcelo Saavedra

Chapter 2:  Preparing for an Observing Session

1. By using planetarium software and MPC data, prepare your observing session.
   
    
2. If you are beginning in this passionate world, it is better to go for slow and brighter objects first.  MPC requires the observing and measuring of objects numbered in the catalogs between 400 and 40,000 to obtain an observatory code number.  They are slow and bright enough to obtain observing experience.  Low numbered objects (0 to 399) already have well established orbits and additional data really does no good.  By asking to go for higher numbered asteroids, a dual purpose is served:  first, to check on the quality of the measurements and, second, to contribute useful data.  But, the lowered numbered asteroids are not ignored entirely.  They are often picked up by most surveys and caught during regular work by others from time to time.  The surveys report data from all detected objects.
   
    
3. If you have some experience in Astrometry, then you would want to choose targets that actually need observations and they would be in the observer’s best interest.  This process is commonly called “follow-ups” and requirements of them can be found on the MPC - Minor Planet Center Web site.
   
    
4. On a typical night doing follow-up observations, you could start out with a list of say, 10 potential targets to have a good inventory of them. Depends on the time needed to get the data for each one, maybe you will not be able to cover all of them, or you may have the opportunity to go for 2 or 3 more.  A fast bright object could require less imaging time then say faint and slow moving objects.
   
   NOTE:  If you are planning to observe slow objects, select 3 or 4 other objects in "near" field areas around the main target to perform a slew between them during the observing session.  Giving enough time for the objects to move is a general rule in astrometry
   
    
5. It is better to locate the target fields with enough separation to do comfortable work and with enough time between them during the whole observation period.
   
    
6. Make sure to calculate the correct optical path to be used to guarantee a good pixel scale (MPC recommend a 2 arc seconds per pixel scale or 3 on the worst of cases) but you must be sure that your used configuration will allow you a correct “seeing” of the objects to be studied and a good PSF (Point Spread Function).
   Take in mind that the MPC’s pixel scale is a recommendation and will vary based on your site seeing.  You have to determine the best spatial sampling for your particular site.
   Since most amateur sites have seeing in the range of 4” to 5” the 2 arc seconds per pixel works out well on average and was selected because this scale fits the seeing disk at most of them.  Some sites actually have better seeing and can select a different scale.
   To go more in depth into this topic we could recommend excellent Herbert Raab's article “Detecting and measuring faint point sources with a CCD” reading.
   
    
7. Another aspect that should be taken into account is the computer time accuracy.  It is fundamental that the computing time error be less than 1 second.  You must be sure to synchronize the PC clock with a NPT server around the world by using the internet before and during your session.  Also, you will be sure that the time stored in you FIT image header will be in UTC format and not local.  This is very important!  Consult your software manual.

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Copyright © 2006 The Cometary Space Web of Steve E. Farmer Jr.

Last modified 05/31/2007 08:50 PM -0400

This web site has been active since March 1, 2006

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