Fun with the Sun by Michael Spingler
When I was 12 years old I had my first view of the sun with my homebuilt 8” Newtonian. Ever since that day I have been hooked on solar astronomy.
My first solar filter incorporated a Hershel wedge design. This system used a non-aluminized diagonal which was inserted into the eyepiece holder, and very dark neutral density filter. The non-aluminized diagonal transmitted approx. 5% of telescopes light to the neutral density filter. Since 5% of the available light (and heat) were still going through the neutral density filter, and 100% of the available light passes through the optical tube assembly before reaching the filter, this solar filter design was not very safe. The neutral density filters were known to heat up and crack (mine did), allowing damaging sunlight to enter the eye. The Hershel wedge has largely been replaced by solar filters that are placed over the front of the optical tube assembly, filtering light before it passes through or is reflected off any optical surface.
Next I bought a Thousand Oaks Type 2 solar filter. Although this filter was a vast improvement of the Hershel wedge filter, this filter gave a false orange-yellow solar image. This filters performance is also dependent upon the accuracy of the optical surface which has been known to vary widely from one filter to another.
After doing some research, several reports indicated that the new Baader solar filter was superior to all other white light filters. I decided to buy one for the C-8 that was on loan to me from CCAS. I was so pleased with the filters performance that I bought another Baader filter for my new TEC 10” f12 Maksutov. Images of the sun in white light were the best that I had ever seen. The Baader filter contains a film surface that does not affect optical performance; a great advantage to using this type of filter design. Because of the superior optical performance, faint details like faculae and granulation were much more apparent.
There was one area of solar astronomy that I had always longed to explore — viewing the sun in Hydrogen Alpha. Twenty four years ago I had my first view of the sun in Hα at Mt. Pinos. I was determined that some day I was going to purchase a Hα filter system. One year ago this month I finally purchased a Daystar Hα filter system and I have been having a wonderful time viewing the sun on a regular basis. Next month I will share some of my experiences viewing the sun with my Daystar Hα filter.
Now let’s address the exciting world of Hydrogen Alpha viewing. This article is not going to be very comprehensive in scope since I am going to refer all of you to what I consider to be the best web sites available regarding Ha viewing and technology.
After getting my first view of the sun in Ha over 20 years ago, I decided that some day I was going to get a Ha filter for my telescope. Each year at the Riverside Telescope Conference I observed with a man who had a 2” f/30 refractor that was used exclusively for Ha viewing. While other people were forming lines around the latest and greatest big Dob’s every night, I felt that I had the best seat in the house viewing the sun through this little scope each day of the conference. The next year I could not wait until I got back to the conference to again view the sun through this marvelous little instrument. It was at this conference that told one of our CCAS members, “If I could only view one type of astronomical object, it would be the sun in Ha”.
Finally in 2002 after more than 20 years of waiting, I finally got my dream system; a Daystar .6A ATM Ha filter system! This last year has been one of my most exciting of all of my 39 years of astronomy. One thing that makes Ha viewing so exciting is that unlike most other astronomical objects that show little if any change over the course of time, the sun is constantly changing! As I am writing this article my scope is tracking the sun in my backyard; and I am going to see quite a difference in solar detail when I return to my scope.
(Oct 9, 2003 3:00pm PDT. I have just returned from my telescope after taking a short break from writing this article. During the short time that I have been writing this article a very small prominence that had just developed has exploded into a HUGE prominence; the largest prominence that I have ever seen! It is approximately 70,000 miles long tip to tip, and is rising about 50,000 miles above the surface of the sun.)
I have often been asked how I chose my particular filter. Ha filters come in various bandwidths. One can purchase filters that have a bandpass as high as 1.0 ångström, to a low of .2 ångström. High bandpass filters are much less expensive, are excellent for showing prominences around the solar limb, but are very poor for showing surface detail. Low bandpass filters are much more expensive, show excellent surface detail, and still show fairly good prominence detail around the solar limb. I chose a 0.6 ångström filter which allows me to see excellent surface detail and still very good at revealing prominence detail.
When one is comparing one Ha filter system to another one has to be very careful to use the same power in each telescope. I have often seen Coronado Instruments set up several of their Ha systems using a short focus refractor and a low power eyepiece to yield approximately 40 power. The views are very sharp and have very high contrast due to the small image size and the minimal effects of the atmosphere at low power. One can look at these systems and then go to another filter system which is using a more modest power (say 100x) and come away with the belief that the first system outperforms the second high power system. This is equivalent to a person looking through one telescope at Jupiter at 200x on a night of average seeing and then going to another telescope and view Jupiter at 500x and coming away with the belief that the second scope was a poor performer because of the large boiling images.
I am going to predict that just like 1980’s which was the decade that the dobsonian telescope came into prominence, and the 1990’s was the decade of the refractor, the first decade of the 21 century is going to be the decade of Ha solar viewing. Do what ever you need to do to get one of these marvelous Ha filters systems. Starting at less than $1,000 , I promise you that it will revolutionize your astronomical viewing.
Editor’s Note: For Baader information, click here. There you will find information on how to make your own solar filter using their (around $10) film for your telescope.