WFPC2 at the Smithsonian

In the recent servicing mission of the Hubble Space Telescope (HST) this past May, among other things, the astronauts installed a new camera, fixed an old one, and brought another camera back to earth. The camera they brought back is called the Wide Field Planetary Camera 2, or WFPC2 for short. (Pronounced "whiff-pick two.") WFPC2 has been the real workhorse on HST for over 15 years. It was the camera that was used to take many of Hubble's most famous pictures, including:

The Pillars of Creation:

The Hubble Deep Field:

And perhaps less famously, but more important to me, it took much of the data I used for my dissertation. (Sorry, no pretty picture for that one.)

Now for your astronomy lesson for the day: you will notice the strange step shape of the above pictures. (That is, much of the upper right corner is missing from the picture.) This is due to the design of the WFPC2 camera. It is actually not just one camera, but rather it is a camera made up of four individual cameras. (We call them CCDs in astronomy -- stands for Charged Coupled Device). There are three "wide field" cameras, and one "planetary camera." (Hence the "WF" and "PC" part of its name.) All four CCDs have the same physical dimensions: 800 by 800 pixels.* The three WF chips have the same resolution and field of view (that is, the amount of area on the sky that the CCD can image is the same), but the PC chip has a much high resolution, and, in turn, it covers a smaller area of sky. As a result, when the four CCDs are combined to form a mosaic of something, the PC chip appears to be smaller because it is scaled to match the resolution of the WF chips. Hence, the "step" shape in the upper right quarter. (That is the PC chip.) Also, if you look closely, you can see the "seams" between the four quadrants of the picture. Try and see if you can see them. Click the images, it's easier when they're big. (It's especially easy to see on the Hubble Deep Field.)

To help you visualize the orientation of the cameras, here's a schematic of the four cameras together (as they would look on the sky), taken from the WFPC2 handbook:

So anyway. The astronauts brought WFPC2 back in May, and sometime in November, the camera arrived at the National Air and Space Museum in Washington, D.C. It will be there until mid-December, when it is going to basically go on tour. But it will be back sometime in March.** But I wanted to see it before it left!

This past Saturday I was heading to DC anyway, so I wanted to make a stop. My friend Freddy (who was also invited to the birthday dinner I was going for) drove with me, and didn't mind making the stop.

We got to the museum, and I knew right where it was. (Right by the model of HST.) As we approached the gallery, we noticed they were roping it off. We asked what was happening, and they said they were closing that part of the museum early because of some private party. No!! We asked a few more workers, and they all told us the same thing. We finally asked someone who looked like they were in charge, and she told us the same thing. We explained that the camera was all that we wanted to see. Fortunately, Freddy remembered to play the, "But she's an astronomer!" card. (I still can't believe I didn't think of that.) That did the trick, and she said that she'd let us in for just a few minutes. So we had to be quick. I gave Freddy my camera, and he took some pictures. So here it is!


It's about the size of a baby grand piano. This black box holds lots of cool optics inside it, including the four CCD cameras.

Seeing it was really cool, even if we did have to hurry. The display is so new (and technically still temporary) that they don't even have any plaques or signs up yet. So you have to actually know what you're looking at. :) I'm sure that I'll go back sometime again after it comes back in a few months.

One last picture. Me and WFPC2! It was like meeting a celebrity. Seriously.



* Unlike your digital camera, in astronomy we don't measure the resolution of a camera in terms of the number of pixels (or megapixels) it has. Rather, we talk about the "plate scale," which is how much of the sky one individual pixel can see. This is why two cameras with the same number of pixels can have different resolutions.
** There is a huge astronomy conference in DC the first week of January. I think having WFPC2 not there when its most interested audience will be in town is really, really poor planning.