ASTROMETRY – MEASURING TRAILS
By using the formula described in Stephen Laurie’s article, ‘Astrometry of Near Earth Objects’, one can avoid fast moving asteroids producing trails on images. However, if for any reason, a trail results all is not lost.
The exposure time of the image of NEO 2002 NY40 shown below was 15 seconds. The asteroid was moving so fast that it produced a trail on the image. It is still possible to measure the position of the asteroid using a software package such as Astrometrica.
After loading the image and invoking the astrometry tool the cursor is positioned on one end of the trail and the ‘Ctl’ key pressed and held down while left clicking with the Mouse. Using the ‘Ctl’ key ensures that the cursor remains in the indicated position. If the ‘Ctl’ key is not pressed Astrometrica will attempt to centre the cursor on the asteroid image. The difference in cursor positions can be seen by comparing the image below (‘Ctl’ not held down) with that above (‘Ctl’ held down).
An extract from the Minor Planet Center report generated by Astrometrica is shown below. The same time has been recorded for both measurements and these need to be corrected before submitting the report to the MPC. In this case 7.5 secs need to be added to the first entry and deducted from the second one (the exposure being 15 secs duration).
Two measurements for the price of one so to speak !
K03N40Y C2002 08 17.92566 19 52 13.01 +19 44 46.2 13.4 V 940
K03N40Y C2002 08 17.92566 19 52 15.20 +19 44 15.6 13.3 V 940