Starter's Guide to Solar Observing with the ALPOSS
by Paul Maxson ALPO Solar Section Recorder
The ALPO Solar Section strives to obtain systematic observations of the sun, both photographic and drawings, to aid professional astronomers. Our members observe the sun in either white-light or monochromatic (usually Hydrogen-Alpha) or both, producing photographs and/or drawings. We are interested in Sunspot Morphology, how a spot changes over time, as opposed to numbers of spots. To date our observers have made over seven thousand photographs and drawings. The demand for our observations is high, and you can help! With a properly filtered telescope you can be producing high quality observations that will aid professional astronomers in advancing solar knowledge.
You can make meaningful observations with telescopes as small as 2.4" and rarely need apertures in excess of 6". If your telescope has a focal length of 35" or more you can produce very usable full-disk photographs. The ALPO Solar Section highly recommends that you filter your telescope BEFORE the objective. There are two basic types of White-Light solar filters, glass and aluminized mylar-type. If you scan Sky & Telescope or Astronomy magazines you will find a number of vendors for these filters. One vendor, Tuthill, Inc, offers a discount to ALPOSS members.
If you buy a glass filter, try to get the "photographic" filter so if you decide to do photography you can keep your exposure times to a minimum (1/500-1/1000 sec). It is important to try to get the highest quality glass filter you can, and always be on the lookout for hairline cracks that can cause filter failure at the worst possible time. THESE FILTERS ARE OPTICALLY TOO THIN FOR VISUAL USE AND CAUTION MUST BE EXERCISED AT ALL TIMES!
With mylar-type filters, it is best if the filter comes in two layers. Tuthill's filters come this way with one layer twice as thick optically as the other. Use the thicker of the two filters for photographic work as this will also allow you to make the shortest exposures. When the aluminum starts to scratch to the point that you are seeing flares in the eyepiece, it is time to replace the filter.
In either case, by keeping the filters as thin as possible, you can get the shortest exposures photographically and if you want to do visual observations you can just use a polarizing or colored filter in addition to the full aperture photographic filter. Another advantage to thin filters is that you can experiment using different colored filters to try to enhance the contrast of the sunspots in your photographs. It is a very good habit to make sure that the very first thing you do before observing is to put on the filter and the very last thing you do after observing the sun is to take off the filter.
Hydrogen-Alpha observations give you a totally different look at the sun. The technique is little different from white light photography, though the equipment necessary is a lot more expensive. Our H-a observers typically use a filter of .6A or less. Hydrogen-Alpha filters typically require a focal ratio of F/30 or slower, which means stopping down your scope by 3-4 times (i.e. an 8" f/10 will be stopped down to about 2.5"), and also an increase of exposure time. ALPO Solar Section members have produced some extremely high quality H-a observations. Again, there a number of vendors who sell these type of filters.
The ALPO Solar Section uses photographs and drawings. Full disk photographs are very important. With any solar photographing session you should strive to produce at least one full disk photograph. Black and white is by far the easiest to do and preferred. Tech Pan 2415 is the film of choice and should not be commercially developed. I use the developer, HC-110 Dilution B, (which dilutes the solution 7:1) for about 2.5 minutes after 1/500 second exposure at F/10 with a single layer (thicker) of Tuthill Solar Skreen using a #47 Wrattan filter. The key is persistence, keep trying and don't be afraid to experiment. Try different times of the day to see when the seeing is best for your location. I found that for my location early morning is best, in fact I will be out observing and photographing the sun as early as 7:00am. Once you find a good combination, stay with it and refine it. Solar photography can become almost routine once you have a method. For higher resolution work, I find that eyepiece-projection works best. I seldom go slower than F/30 for high resolution, but again experimentation is best. Print your negatives on 8x10 paper, making the image as close to 170cm as possible. Make copies of the enclosed summary sheet for the appropriate type of photography (White-light, H-a, or High Resolution) and fill it out as well as you can. The most important information is the date/time and equipment used. I can obtain the Rotation number if you can't. I have an IBM computer program that calculates this and can provide it for you if you provide me with a disk, mailer and postage. SESC regions are a bit more difficult. If you have a modem you can call the SESC (1-303-497-5000) for daily region reports. With these tips you can get 2" resolution on full disk photos and near 1" resolution on high resolution photos in white-light and probably a bit less resolution in H-a. A photo of 3" resolution is typical and valuable to the professionals.
A good drawing can help the professional determine sunspot positions. A full-disk drawing will rate about 5-10" resolution mainly because that's about as accurate as one can get in positioning sunspots on the drawing. You should use the enclosed drawing template for consistency. It's probably best not to "color in" the sunspots, just outline them. Draw the umbra shape first, then the penumbra around the umbra. Try to locate the spot's position on your drawing as closely as possible. This comes with practice. A good drawing need not take more than 5-10 minutes to make, and probably less with practice. If you have a real artistic flare and are patient, you can do hi-resolution drawings of selected groups. Here you might want to experiment with "coloring in" the umbra or penumbra to show finer details on the selected group.
For the standardized report forms contact:
Paul Maxson ALPO Solar Section Recorder 8839 N 30th Avenue Phoenix, Arizona 85051 USA