Asteroid 1994 PC1’s Close Flyby

(7482) 1994 PC1 is an asteroid of about 1 km in diameter belonging to the NEO (“Near-Earth Objects”) category. NEOs are solar system objects that periodically make relatively close encounters with the Earths, and thus pose a potential threat to our planet. 

On 18th January 2022 this asteroid made a close approach with a minimum distance of a bit less than 2 million km, i.e. about five times the average Earth-Moon distance. While this distance is still relatively safe, not many objects get so close to Earth.

Thanks to the close approach, the asteroid became relatively bright, with a peak of magnitude 10.2, which made it observable through small telescopes. Moreover, the circumstances were optimal for the northern hemisphere, as the transit took place in the constellations of Pisces and Andromeda, which are still fully visible in the first part of winter evenings. A stable high pressure area lingering over Central Europe, including Northern Italy, offered an opportunity not to be missed!

So I pointed my rig (a Celestron C11 SCT + an ASI 071 MC Pro camera) at the asteroid. Rarely have I seen a celestial object travel so fast: the focal length of my scope produces a 29-by-19 arcmin field, and the asteroid could be seen moving in a matter of seconds.

1994 PC1 traveled a distance of about 23.6 arcmins (i.e. ~1400 arcsecs) in the field of view in about 10 minutes, yielding an apparent angular speed of 140 arcsec/min or 2.3 arcsec/s. Considering an image scale of 0.36 arcsec/pixel, this means the asteroid was drifting at more than 6 pixels per second on the sensor. At a distance of about 2000000 km, this yields an actual speed of 22.3 km/s, i.e. more than 80000 km/s.

I have two acquisitions of the asteroid’s close flyby. One is a composite of 13 30-second frames I had to crop because of frosting on the top area of the detector. The second is a movie made from about 100 3-s exposures that clearly shows the asteroid zipping through the sky as time passes by.