Lasers on Telescopes

For me, the phrase “lasers on telescopes” brings to mind super villains capturing top secret astronomical facilities in order to execute a nefarious plan. I think of Mr. Freeze capturing Gotham Observatory to build a giant freeze ray in the movie Batman and Robin. Perhaps a funnier and better example is Chairface Chippendale using a laser in a telescope to deface the moon with his name in the TV series The Tick.

Laser measuring tool (on yellow arm between black mirror covers) over the Mayall primary mirror.

In fact, lasers are used on telescopes. Perhaps the best known real-world examples are telescopes that use laser guide stars. This is a technique where astronomers fire a laser mounted on the telescope into the sky. The laser light is scattered by the atmosphere, but optics in the telescope correct that light back into the proper size beam and also correct the stars seen at the same time. We had a system like that at the 2.1-meter telescope at Kitt Peak run by CalTech. There was also a system like that at the 3.5-meter telescope at New Mexico’s Apache Point Observatory.

Now, these lasers are not ones that are likely to be co-opted for nefarious purposes by super villains. Lasers used for guide stars just aren’t that powerful. That said, they can’t be used with impunity. The artificial guide star laser at Kitt Peak was visible in the ultraviolet band and would interfere with optical telescopes also observing in that band. What’s more, I’ve been told Apache Point Observatory had to clear laser firings with the Air Force, who had a base nearby. The observatory’s laser wasn’t likely to shoot down planes, but we could imagine tragic results if a pilot happened to fly through a laser’s line of sight only to be blinded.

This past week, while working at the Mayall 4-meter telescope, we were also using a laser. In this case, it wasn’t fired at the sky, but the laser was mounted on the telescope’s mirror cell and fired at different surfaces on the telescope to get precise measurements. Now that the refit for DESI is nearing completion, the engineers need to make sure everything went back together as it was designed. They need to make sure all the new parts are placed in just the right place. If not, this is the time to make adjustments. Measurements of telescopes are important because they help to assure that astronomers can focus the telescope properly. Precise measurements are also critical to determine the proper weight distribution of the telescope, which in turn helps it track the sky precisely.

As it turns out, I also spent part of this past week working on an adaptive optics system a little like those laser systems I mentioned. However, the WIYN Tip-Tilt Module doesn’t actually use a laser. Instead, it takes precision measurements of an actual star and uses optics within the instrument to bring that star as close as possible to a precise point. I’ve seen it used to deliver incredible image quality with stars only 0.3 arcsecs across. To put that in perspective, star images with WIYN are typically more like 0.8 arcsec across. The size difference is the result of atmospheric blurring.

This all echoes something I’ve been saying in the past few blog posts. If something isn’t quite right, there are ways to fix it, even when its a multi-million dollar scientific project. By comparison, books are much easier to fix. It’s why beta readers and editors are so important to the writing process. They help us see places where we didn’t express ourselves clearly, made something work in an artificial way, or simply used the wrong word. It’s part of why reviews are so important. Reviews help customers, but they also help writers because they tell them what worked and didn’t work.

Over the years, reviews helped me refine my craft until I could write books like Owl Riders and Firebrandt’s Legacy. And yes, reviews are helping me shape the 25th anniversary edition of The Pirates of Sufiro, which I’m working on right now. I hope you’ll join me on a journey to one of the worlds I’ve created and, if you do, please leave a review to let me and others know what you thought. The titles in this paragraph are links where you can get more information about the books.

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