ASTROMETRY –
MEASURING TRAILS
1.0 Introduction
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.
2.0 Astrometry
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).
2.0 Timing
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