Wednesday, March 31, 2010

The deep end of the pool

I have often commented here on the APOD (Astronomy Picture of the Day), usually of some astonishing star-birthing nebula or swirl of galaxies, something that drags us breathlessly into the universe of the eons and infinities. Here is pic that offers a quieter beauty -- the Moon traversing the Pleiades -- something our remotest ancestors might have observed, although not in such subtle detail. Click to enlarge.

The Seven Sisters was an ancient name for this cluster in Taurus. Most folks can only see only six stars, the six brightest you see here. Some observers have claimed to see a dozen or more stars with the naked eye, although certainly not with the Moon in such close proximity. The most I have seen is nine, many years ago on a night of unusual clarity when my eyes were young and sharp. There are in fact hundreds of stars in the cluster, born together from a nebula whose wisps and streamers still wrap the newborns in swaddling clothes.

It takes just over a second for light to reach us from the Moon. The Pleiades cluster is 440 light-years away, 12 billion times farther. Think of it this way: If the Moon were at the tip of your nose, the Pleiades would be as far away as the Moon.

And what about all that black in the photograph, like the background in a painting by Caravaggio? Point the Hubble Space Telescope into any patch of that darkness, say the square I have outlined with a white box, leave the "shutter" open for ten days, and you'd see 10,000 galaxies, far far beyond the Pleiades. Anyone who can grasp that fact and still believe they know the answers to the biggest questions is more confident than me.