Another Low-Flying Space Rock
By Chuck McPartlin
On Wednesday evening, October 11, an approximately 50-foot across Potentially Hazardous Asteroid named 2012 TC4 made a close flyby of the Earth, passing within about 32,000 miles, or about 13% of the distance to the Moon. Astronomers around the world monitored its passage, as a sort of test run for defending the Earth in some future asteroid encounter.
For Santa Barbara, TC4 was low in the SSE at the end of twilight, and rapidly heading lower, so imaging it was a race between twilight, TC4’s rotational aspect, its altitude above the horizon, and atmospheric extinction, the dimming caused by looking through more air near the horizon. But TC4’s window of maximum brightness coincided with its window of visibility for me, and so it was catchable.
Here’s is the video, not speeded up, of TC4 zooming past at around 7:50 PM PDT. It looks like a streak because the video camera was integrating for 256 frames, or about 8.5 seconds, to capture enough photons from the asteroid. For a sense of scale, the entire frame is just a bit smaller than the Full Moon.
Relative to us, 2012 TC4 was going about 4.7 miles per second, which is actually rather slow, and it was close enough to us that the Earth was substantially altering its orbit as it cruised by.
The asteroid has a relatively fast rotational period estimated to be a bit over 12 minutes, and it varies by about 1 magnitude (2.5 x) in brightness over that period, so it is probably elongated rather than spherical in shape. Indeed, when I last saw TC4 at about 8:16 PM PDT, it was barely detectable.
There are probably lots of new articles and radar images of 2012 TC4 coming out today, but below are some good information sources as of Wednesday evening.
References for a Cloudy Evening