Astronomy with lasers

As I said in the last post, I’m on the mountain for the next week or so. I’m just working the last quarter of the night for the next few nights, commissioning a new instrument at the JCMT. So I made my way up to the summit leaving the Hale Pohaku Hotel & Resort for Stray Astronomers at about 1:30am. The sky was beautiful and clear – it is one of the natural wonders of the world, truly amazing and I never, ever get used to seeing the night sky from the summit. However, when I looked over at the ridge above us where the biggies are (Subaru and the two Kecks) I noticed this bright orange line shooting out of the Keck I dome into the sky. No, not James Bond, but adaptive optics with lasers.

The technology is actually quite cool. At Keck they call it LGS – laser guide stars. Of course adaptive optics with natural guide stars (NGS) has been around for a while, but it depends on the presence of stars near where you want to observe (within about 30 arcsecs or so). Despite there being “billions and billions” of stars in our Galaxy, apparently this leaves something like 99% of the sky unviewable with adaptive optics. Hence the genesis of this new technology. The laser is shot up in the direction of the astronomical object of interest where it interacts with the sodium layer high up (about 90km) in our atmosphere. The sodium atoms (which got to be there by virtue of meteor strikes, etc, by the way) are excited into emission by the laser and the telescope uses it as an artificial source to correct the aberrations that are introduced by the atmosphere.

All pretty cool and it looks cool as well. I happened to have my camera with me (!) and so went to the back of the JCMT, onto the gantry and set up a long exposure on a tripod. This is what I got:

Not that great, but cool nonetheless. If you look closely (click on the images) you’ll see double stars and two lines for the laser. That’s because the way that the JCMT telescope is built, the whole building rotates when we follow sources around the sky. So the double stars and laser tracks are because the telescope moved in the middle of my exposures. (We’re not going to stop working just because I want to take a photograph!). These were a 1.5 and 3 minute exposures, respectively.

If the lasers are out again in the next couple of nights I’ll set up the tripod outside and see if I can capture a better shot. In the meantime, here’s a really nice image from the Keck website.