Joint Observation of Asteroid 2000 GD2 from Munich and Verona

17.3.2002, EurAstro Munich and CAV (Circolo Astrofili Veronesi), Pleiade Observatory Verona

Mid of March 2002, an asteroid of the so-called NEO ("Near-Earth-Object") class, came relatively close to the Earth. "2000 GD2", so the name of this asteroid, was a rather dim object of 14.2 magnitudes only. Because of its relative closeness to Earth, it showed a rather fast movement against the background stars, and was easily detectable on images with longer exposure time (3 minutes) as a streak:

As the asteroid was so close to Earth, there was good chance to measure its parallax, i.e. the apparent difference in its position when simultaneously observed from different locations on the Earth's surface. If such difference in position could be measured, also the distance of the asteroid could be calculated by simple triangulation.

So it was planned that members of EurAstro Munich and our partners from CAV in Verona take images of 2000GD2 at exactly the same time, and that these images should be compared to find any differences of the asteroid's position. Below you see the pictures taken from Munich and Verona at 22:04:00 UT. The asteroid is marked with an arrow. At first view, the pictures look nearly identical:

If however both images are stacked so that the stars match exactly, the difference in position of the asteroid is, as Flavio Castellani from the CAV, Pleiade Observatory Verona noted: "small, but evident". In the following animated image, the pictures from Munich and Verona have been combined so as to match the images of the stars as good as possible. Note that the asteroid is "jumping", indicating a difference in position:

Indeed, when determining the exact positions of the asteroid with suitable astrometry programs, a difference (parallax) of 4.5 arcseconds was found. From such parallax, the distance of asteroid 2000 GD2 to the Earth is calculated to be approximately 11 million kilometers.

A composite of the images from Munich and Verona shows the asteroid (indicated by an arrow) at different positions, appearing as a "double star".

This was the first time that members of Astro Munich measured an asteroid's parallax and distance. The images were obtained with a C8 and ST8 CCD camera (Munich, M. Rudolf) and a 60 cm reflector and ST6 CCD camera (Verona, F. Castellani).