Monday, April 25, 2011

Going the distance


Here is a stunning Hubble Space Telescope photo that was the APOD (Astronomy Picture of the Day) last week. Two galaxies, collectively known as Arp 273, encountering each other so closely that gravity is distorting their spirals. Two galaxies engaged in a cosmic dance. Click to enlarge.

Let me say a bit more about what we are looking at than APOD provided.

Two galaxies, one neatly wrapped, one with out-flung arms. The one at the top is about the size of our own Milky Way galaxy, although more lop-sided due to the gravitational pull of its partner. Perhaps it contains a hundred billion stars, separated (as in the Milky Way) by light years. We are seeing in the photo only the relatively rare and exceptionally bright blue and red giants. If we were on a planet of a sun-like star in the upper galaxy, oh how magnificent would be the companion galaxy in our night sky!

The bright stars in the photograph with diffraction spikes are in our own Milky Way, very much in the foreground.

Imagine our Milky Way Galaxy -- a hundred thousand light-years wide -- as a dinner plate. We are on a planet of a star about two-thirds of the way out toward the edge. When we look at Arp 273 we are looking down and out of the dinner plate, at an angle to the plate and towards the edge. The Arp 273 galaxies would be a dinner plate and a salad plate about a kilometer away. (The nearest spiral galaxy to us, the Great Galaxy in Andromeda, would be a dinner plate just across the room.)

Arp 273 takes up about as much of the sky as would a pinhead held at arm's length. And look what else is in the photo. I count at least a few dozen other galaxies, vastly more distant -- all those little elongated blurs in the background. Every one of those galaxies contains hundreds of billions of stars. If you can wrap your head around all this and still think the Creator is attending to your prayers, you have a more robust imagination than me.

(I can hear my dear departed mother, the classical grammarian, saying, "Than I, Chet, than I.")