Learning to Capture the Sun

The Public Observatory Project is just over a year old now, and in that time we’ve been  experimenting with the telescope to discover what is visible in the daytime sky and devise ways that our visitors can have the best experience possible.  One of our goals is to use our equipment to take images of the Sun, so that we can share our star’s day-to-day activities with the visiting public as well as those who can’t make it to the Mall to look through our telescopes.  We wanted to capture true-to-life images of the Sun as it appears through our telescope and make interesting features clearer and more apparent.

It would be dangerous to use a normal telescope to look at the Sun because the Sun’s concentrated and unfiltered light would damage your eyes.  One of the tools we use to look at the Sun safely is our Lunt Solar Systems hydrogen-alpha telescope that filters out all but one wavelength of red light. This makes it safe for viewing a part of the Sun’s atmosphere, called the chromosphere.  To take images of the Sun, I started out with this telescope, as well as a Lumenera SKYnyx 2-0 Color camera that fits where the eyepiece usually goes. We also have a laptop with software to control the camera, called Lucam Recorder.  With these in hand, I set off to take some of my first images of the Sun.

This image of two prominences was taken on June 8, 2010.

Through some experimentation, I found out that different exposure settings revealed very different details on the Sun. First I cranked up the exposure to capture the faint prominences coming off the edge of the Sun and took a series of images. Next, I turned down the exposure to what I thought was an appropriate level to capture details on the Sun’s surface before taking a second series of images. I used a processing program called the GIMP to merge the two images by selecting the disk detail and moving it on top of the prominence image.  But, something wasn’t quite right. This didn’t look much like what I was seeing with my own eyes. So, I turned to a local amateur solar imaging expert and friend of the National Air and Space Museum: Greg Piepol.

Greg’s solar imaging work, which you can check out on his website sungazer.net, has been praised for its beauty and attention to detail. My colleague at the Observatory and fellow Sun imager, Katie Moore, and I were thrilled that he agreed to come into the Museum and show us how he captures such stunning images.

Greg taught us several things that improved our imaging. The first and most important was that we had been drastically overexposing the disk of the Sun, which washed out the details we were trying to capture. Greg also taught us how to better use an image stacking program called Registax, which takes individual frames from a movie file and stacks them together, thereby removing a lot of noise caused by Earth’s turbulent atmosphere. Astronomers call this "seeing," which is what makes the stars twinkle. He also showed us other image processing techniques in the GIMP, such as levels adjustment and color correcting that brought out details on the Sun.

This image was taken on July 28, 2010, the day after Greg Piepol came to visit. The small dark Sunspot near the top of the disk is about the same size as the Earth!

This was most certainly closer to what we had seen in the telescope. But of course, as they say, practice makes perfect. Over the next few months I took pictures as often as I could. I learned the extreme importance of making fine adjustments to the filters inside the telescope to get exactly the right details. I learned the advantages of using a double-stacked filter on top of our telescope to help make the darker wispy absorptive lines in the solar atmosphere, called filaments, truly pop out.  I also learned the importance of careful processing to coax the most detail possible out of the raw data.  It is interesting to compare the final product to one of the raw, unprocessed images to see what a difference it makes.

This final processed image of a Sunspot was taken on July 30, 2010

A large prominence on the Sun, taken on September 15, 2010

This mosaic of 2 images highlights a large Sunspot group, as well as a dark filament in the Sun’s chromosphere.

And so, the journey continues! The Sun is always changing, and there are always more techniques to be learned and perfected. If you get the chance, come see the Sun for yourself at the Public Observatory, which is open Thursday through Sunday, 11 am to 3pm for the month of October, weather permitting.  We are ordering an upgraded camera and some new software to better process these images, so be on the lookout for new images online!