First Light in astronomy is an old tradition filled with all sorts of interesting history. Some first light examples are not the best, while others are just tremendous. Ours was a little of both with the first exposure of the 0.7m telescope to the nighttime sky. Don’t worry! It all turned out just fine!
The vert first exposure of starlight to the telescope was last week: Conditions were good with a nice clear sky and freezing temperatures. The wind was calm. The telescope had never been focused before and had yet to have a pointing solution…. so it really had no idea where it was looking. We decided to aim it in the general direction of Orion and take the first images. Of course, they were blurry. The scope had never been focused before. At this point we got the CCD imager into automatic mode, making it take an image every second, non-stop so that we could run the focuser until we had the images nice and sharp…. out the focuser went, and the star images got smaller and smaller and smaller, then “kachunk!” The focuser had run out of travel, and the star images were not quite in focus yet! The imager was perhaps a few millimeters away from achieving a perfect focus. The good news was that this was more than enough to engage in the time consuming process of collimating the primary mirror. A few hours later we had aligned optics, but we had to order a small spacer ring to push the CCD imagers little further out.
The interesting thing about this telescope’s control software is the building of a pointing model. By taking a series of images all over the sky, the software does an astrometric reduction on each image and measures the slight variations in the telescope’s true pointing versus where it thinks it is pointing. This takes care of all sorts of interesting issues: flexure in the pier, telescope and mount, mirror sag or flop (none here!) and general pointing. After some 20 images, we were able to point to any object in the sky and have it show in the images we took… just like that image of Betelgeuse above.
Once the spacer arrived this past Wednesday, we went out to install it and then wait for darkness to arrive. It was a nice clear and very cold night. The goal was to build a large pointing model and take some images of famous deep sky objects. I also wanted to test out a start-up and shut-down procedure that I had typed up earlier in the week. That evening, we started everything up: the dome was homed and set to track the telescope. The CCD imager was on and cooled to -30ºC. The telescope was on, homed and tracking. Would it reach focus! Absolutely! It was spot-on perfect. We then built a large pointing model with over 100 images. Now the telescope would find and center objects of our choosing, and it would track them for better than five minutes without needing any autoguider corrections. This is quite the telescope!
We chose some of the iconic late winter deep sky objects to share with you for official first light. These are all composites of four filters:
- Luminance: a clear filter
- J-C Rc: which was used as the red channel
- J-C V: which was used as the green channel
- J-C B: which was used as the blue channel.
The V, B, and Rc filters are Johnson-Cousins photometric filters used for photometry, the science of measuring brightnesses, which can lead to our understanding of an object’s surface temperature and size, among other things.
You might want to dim the room lights to see the details. Also, click on the images to see in a larger format. Enjoy!
The next phase of this telescope’s use will be to collect scientific data. We have already taken images of U Gem and V Ori to calibrate our photometry and to see if we can produce good data for scientific publication. It has passed with flying colors thus far!