Stellar Numbers for an Eclipse

Last night, 824 Anastasia, an asteroid the size of the tiny Caribbean island of Barbados, passed directly between Earth and the star, Zeta Ophiuchi, briefly eclipsing the light of the star if you were watching it from within a narrow 25 mile path that cut across the western United States and Canada.

There are hundreds of thousands of asteroids and billions of stars, so it’s not all that uncommon for an asteroid to cross in front of a star, but this particular occultation drew more interest because Zeta Ophiuchi is easily visible to the naked eye. So, if you happened to be in the right place at the right time, you would have actually seen a bright star winking out for a few seconds for no apparent reason, which is very rare event indeed.

But it’s the sheer scale of the numbers involved in this event that boggles my mind. 824 Anastasia, only 21 miles across, is about 2 million miles from Earth, and Zeta Ophiuchi is over 2.7 thousand trillion miles away, and yet for a few brief seconds, that tiny lump of rock floating in the depths of space between Mars and Jupiter intercepted a stream of photos that had been making a bee-line toward Earth for over 450 years. And what’s more, even with the vast distances involved, we actually have the ability to predict these occultations well before they occur, right down to the time and place on Earth where they can be seen.

Well, almost. It seems that the eclipse took a more westerly path than was predicted, and from the one web site I found that had some preliminary information from those trying to observe the event, only 3 out of 33 people reported seeing it.

Ah well, I guess that’s not too unexpected given the, er, astronomical numbers involved.