Astrometry or the science of accurately measuring the positions of objects has undergone a renaissance with the advent of CCD cameras. This task was previously the domain of Professional Observatories, who used expensive glass plates and dedicated measuring engines to accurately determine the position of a star, comet or minor planet.
Affordable CCD cameras and inexpensive yet powerful personal computers have changed the way Astrometry is now performed. Many small and amateur observatories are now contributing useful, professional quality data for Minor Planet surveys.
Why perform minor planet surveys? If you get to discover a minor planet (and determine its orbit) you may also have the privilege of naming it! There are well over 40,000 minor planets in our solar system. If one, say the size of a Volkswagen, were to hit the earth in a populated area, it would cause considerable damage....hence plotting and reporting their whereabouts is a considerable aid in determining whether these might one day pose a threat to the Earth.
One of the most powerful and intuitive tools for performing Astrometry is CCDSoft and The Sky by Software Bisque. This software allows the stars in a digital image from a CCD camera to be matched with Hubble Guide Star catalogues, with the software delivering a "plate solution" accurate to within one arc second.
The Process is straight forward. CCD images are copied via CCDSOFT to the windows clipboard, then pasted into The Sky
Click on The Sky image link wizard, and the software will search for stars which match the pattern of those in the CCD image.
If a link is found, The Sky will scale and rotate its display to match that of the CCD image.
Once a link is found a astrometric plate solution can be imported back into CCDSOFT.
Once CCDSOFT has the plate solution, you can then click on any object in the image to determine its exact positon. This data can also be automatically formatted into a text file suitable for e-mailing observations to the Minor Planet Centre at Harvard in the USA.
To perform Astrometry using The Sky and CCDSoft software you will also need (apart from a telescope):
While it is possible to use The Sky and CCDSoft without a CCD camera or computerised telescope, however you would need to know the approximate RA and DEC co-ordinates of an image (or the name of an object near the centre of the image), and the image would have to be scanned so it could be loaded into CCDSoft. It is also very unlikely the quality of the data obtained by this method would accurate enough for submission to the Minor Planet Centre, who generally require observations to be accurate to one arc second or better.
- A CCD camera
- Digital Setting Circles or
- A computer controlled mount ( If a telescope is linked to the Sky, either via digital setting circles, or via computer control, a rough set of co-ordinates is saved within the image file data. This position can then be used to start a pattern matching search).
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