As I write (on Wednesday morning), the Hubble Space Telescope is over the Atlantic Ocean, heading for the coast of North Africa. Whoops, no, I just looked again; it has reached the coast of North Africa.
The scope orbits 353 miles above the surface of the Earth, once every 97 minutes. And all the while it's truckin' along, it keeps itself pointed at its target. With exquisite precision.
This in itself is no big deal. All orbiting telescopes do it. Sensors lock onto guide stars and keep the instrument pointed at the same part of the sky. It's like shooting ducks in a carnival gallery while riding on the ferris wheel, with the advantage that the duck is effectively an infinite distance away.
No big deal -- until you think about it. Such a tiny part of sky, and every star within that frame must be recorded without blurring, and meanwhile that massive instrument whizzing around the Earth in 97 minutes. I just looked again. The Hubble is over Saudi Arabia.
We take all this stuff for granted. But the engineering involved is little short of astonishing. The sensors, the gyros, the thrusters. As I write, the Atlantis Shuttle is closing in. The Hubble is getting its last fix. If all goes well, the telescope should perform for another five or ten years. But there'll be no more upgrades or repairs. It's all downhill from here for HST. But, with luck, we'll have a few more triumphs. Among other things, expect an Ultra Ultra Deep Field image, the best look yet at the universe's beginning.
The photo below is from an earlier Hubble servicing mission. Can you identify the geography in the background? What city lies between the Hubble and the elbow of the Shuttle's robotic arm? Click to enlarge.