As I write this, the Space Shuttle Atlantis has just blasted-off a few hours ago, headed for the Hubble Space Telescope. It’s hard to believe that Hubble’s been up there for more than 19 years now, and has helped revolutionize our understanding of the Universe, from measuring the Hubble constant to discovering Dark Energy. It continues to dazzle us even today.
While you can read about the servicing mission that’s going on here, I’m going to focus on saying goodbye to one special instrument this week: WFPC2. (If you want to sound like an astronomer, it’s pronounced WHIFF-pic-too.)
This camera, the Wide Field and Planetary Camera 2, installed in 1993, has been taking some of the greatest pictures the Hubble Space Telescope (or any telescope) has ever seen. Today will be its last day on the telescope, and this week I will be doing a five-part special on the five greatest images this camera has taken over its 16-year history. Let’s cut right to it.
Battle not with monsters, lest ye become a monster. And if you gaze long into the abyss, the abyss also gazes into you. —F. Nietzsche
When you look up into the night sky, in some places there are stars, and in other places is just a black, empty abyss. You can see more stars with binoculars than your naked eye, and more with a telescope than with binoculars. But, at some point, you will have seen it all.
Well, in 1995, they decided to do an interesting experiment with the Hubble Space Telescope. Let’s take a blank patch of sky, one with practically no stars in it, one with no known galaxies, clusters, or — pretty much — anything of interest in it. And let’s point our telescope at it, for days, and let’s see what shows up.
This image is only one degree on each side, or only 0.005% of the night sky. So you can appreciate just how miniscule this area is: the night sky is about 20,000 square degrees, while that little area is less than 0.002 square degrees! There are five faint stars in this field, and — before Hubble — they were the only things we knew of in this area. It looked like this:
Over the span of 10 days, WFPC2 took 342 images of this abyss, staring at this tiny, black patch of sky where nothing seemed to be, counting one photon here, one photon there, and often not seeing a single thing for minutes on end. At the end of 10 days, they stitched it all together, and here’s what they found:
(And click here for the full-size version.)
Do you know how remarkable this is? Every point of light in this image that wasn’t one of the five stars identified up top is its own galaxy! We had no idea how deep, how dense, and how full of stuff the Universe is until we took this picture. Do you have any idea how many galaxies are in this image? Any idea — in less than 0.002 square degrees — how many galaxies there are? Well, let’s just take 3% of this image, blown-up, of course, so you can count.
And remember, every single blob, blur, or distant luminous dot is a galaxy! There’s about 130, according to my estimates, more or less. If we do the math and extrapolate this to the entire night sky in both hemispheres (about 40,000 square degrees), we get that there are 10^11 galaxies in the Universe, or 100,000,000,000 galaxies!
Keep something else in mind here: 100 years ago, we thought we were the only one. I don’t know how I’m going to find 4 other images from WFPC2 to compete with this one, but this is my favorite, and just creating it totally changed our view of the Universe, and how vast and full of stuff it actually is!