Let me remind you what we had started to talk about. The class is organized into three fairly specific topics. The first of which is extrasolar planets. Planets around stars other than the sun. Exoplanets, so-called. That’s our topic. One of the things that I pointed out last time is that, surprisingly enough, very–until ten years ago none of these were known. And it’s only a very recent development that there’s any actual evidence that these things exist. So, one question you might ask is why are these things so hard to find? The science fiction folks seem to have no trouble; they just sort of go around in their spaceships and find these things all over the place. And to consider that question let me show you a picture. Here’s a picture of a star. This is the star Sirius. It’s the brightest. It’s a blow-up obviously of a photograph plus a little Photoshopped arrow. That’s not a celestial object So, this is a blow-up of a photograph of the star Sirius. Sirius is the brightest star in the sky to the–easily visible with the naked eye. In fact, as I say, the brightest star. It’s one of the closest stars. It’s a little bit brighter than the Sun intrinsically, but it’s ten light years away or so.