White light

          I started observing with class Thousand Oaks type visual white light solar filter. This is a 1:100,000 filter that blocks or reflects almost all of the sun light and looks like a mirror. This filter gives the sun a yellow orange color that seems "natural". Mounted on a ETX 90 with electronic controls and a tracking motor allowed me to keep up with the passage of sun spots across the solar surface. I watched them as they rotated in and out of view as the sun lumbers through its 30 day period of rotation. I saw them change. The groups are the most interesting to watch. The spots become more numerous, they spread apart, they develop a surrounding umbra, and then with the passage of time they fade. Occasionally, You can see an individual sun spot split, it is like watching cell division in slow motion. I guess that occurs when the different poles of the magnetic field are splitting and slowly ripping the spot in two. Hmmm.

         With the advent of Baader Solar Film from the Baader Observatory in Germany, I had a material with which to make solar filters for my 6" and 10" dobs. And while I was at it I made them for both scopes finders and the ETX's finder too. I did this as they say the best way to find the sun is to minimize the shadow of you scope. I do this by projecting the scope's shadow onto my shirt or the ground. But I can't get the 'scope aimed to within a degree of the sun (average telescope FOV) using this method, but I can get it within two degrees. Hence the filters on the finders. I minimize the telescopes shadow size, check the finder, center the sun in the finder, move to the telescope eyepiece and I'm ready to view. But I must say that this whole filter on the finder idea works best with a 90 degree mirror on the finder. If your finder is straight through, you need a light blocker that extends beyond the filter to keep the sun out of your eye when you are using a straight through finder.

          Another benefit of the filter on the finder is safety. If you don't filter your finder you should cover it or remove it (better). You don't want a guest or your self to look at the sun through an unfiltered finder. Avoid eye injury! As a bonus, you get a low power view of the sun! The finder is kind of like a one eyed binocular. When I do solar observing with groups of kids, I find that many are as impressed with the finder view as with the view in the main scope. With my 10" dob it lets me have 2 people observe at the same time as my finder and the scope's EP are on opposite sides of the scope.

          Safety is an issue. You can damage or destroy your vision with an "un" or improperly filtered scope. I always check the filters before use, particularly the Baader film to look for defects. Then I confirm that the filters are securely in place on both the finder and the scope. Only then do I look at the sun. And I only use materials approved for solar viewing. Solar observing is "high adventure" astronomy, be careful!

          I like to observe with my 10" 5.6 dob with a full aperture filter. If seeing permits you get occasional high definition views. Some prefer a stopped down image but I've never seen the point. IF the sky allows it you'll get a more detailed image at full aperture. If the seeing is bad then just drop the magnification used for viewing.

          Both the glass and film white light filters let you observe the sun's surface or photosphere. Sun spots with their dark umbra and lighter penumbra are the dominant features. These are often found in groups. These groups represent a tremendous amount of stored energy. With larger aperture the surface granulation becomes more apparent. This subtle grey and white dot like mottling of the solar surface is caused by 1000 Km size cells of gas that rise to the solar surface by convection. They last for about 20 minutes. As they sit on the solar surface they cool and darken, and after they have cooled enough they sink back down below the solar surface. I can see these in the 6" scope but they are more apparent in the 10". Faculae, or slightly brighter areas of the solar surface are seen near the edge of the sun where contrast is better. These are actively emitting areas usually found near sun spots or sun spot groups. In white light there is not much change over a short observing secession, but if one observes every day one can watch the spots move as the sun rotates and see them evolve. The process of sun spot evolution can last for weeks. The larger groups are longer lived. Change, Hmmm - discussing that was what got Galileo into trouble.

           I ran across this on some one else's site. Try color filters for solar observing. Green is supposed to help with seeing granulation, blue with seeing faculae (the Tuthill mylar solar filters were "blue"), and red/orange for seeing detail in penumbra. It might be interesting to combine these with a variable polarizing filter if your scope is "big".

          Later I hope to update this page with more info on solar observing. The background on this page is an embossed sun spot.  My video image galleries contain some B&W images made with a B&W video camera. The Meade electronic eye piece with a infared filter on it is good for this purpose. You don't need a sensitive chip for solar work. The sun is plenty bright.

H - Alpha light

        The chromosphere, the lower solar atmosphere, lies above the  sun's photosphere (surface). Here, trapped by the sun's gravity and  magnetic fields, Ionized Hydrogen gas glows in Hydrogen "Alpha" (red) light. But how to see it? The sun is mostly hydrogen, so it comes as no surprise that it puts out a fair amount of hydrogen light. The dominant type of light emitted by the sun's hydrogen is in the H-alpha band. This light has a reddish orange color. This light can be seen through the use of a filter system or telescope that filters out all light frequencies except for the H - Alpha frequency. The device that lets this happen is called an Etalon (French for very expensive). This uses the cancellation properties of waves to null out all light except for the H - alpha light. Usually the Etalon is assisted in this task by an 'energy rejection filter" that gets rid of much of the IR, UV, and visible light before it reaches the etalon.

          There are three companies that make H-Alpha filters: DayStar and Coronado and Solar view. The Daystar systems are designed for long focal length setups and require a heater (electricity). I assume that the long focal length requirement boosts the magnification and decreases the field of view. The Coronado are designed for short or long focal length scopes and do not require a source of electric power. They make filters (a two piece set up, one for the front end and one for the back end of the telescope) for refractors, SCT's or Mak's. These filters use an etalon with a central obstruction (this patented process makes the etalon easier and a little cheaper to make). The third company is composed of folks who left Coranado. They use 100 year old technology (no patent) to make an etalon that is thermally stable (doesn't need a heater) and has no central obstruction (improved contrast). When I wanted to get an H-alpha device, I did not want to buy a refractor and did not know about mounting a H alpha filter on my ETX, so I bought a Coranado NearStar which is their second generation dedicated H-alpha telescope (after the Helios and before the SolarMax line). This has the advantage that it cannot be taken apart and made unsafe - which is good for someone who observes with children.  It has a 0.8 angstrom wide filter so it is better for viewing prominences then surface detail. The nearStar has a filter tilting screw to "tune in" the H-alpha band.

          The Coronado Instruments NearStar is very easy to use. I attach it to a TeleVue TelePod mounted on a Bogen photo tripod. I can be set up in 3-5 minutes. There is space for a few EP in the scope's case so along with the tripod it is a grab and go system. I keep it in the back of the car so if I get a few minutes in the middle of the day I can run out and see what the sun is up to. I use a Meade 18mm super wide and a Televue 9mm Nagler to observe with it.

           With the NearStar I was able to see prominences (hydrogen gas trapped in the lower atmosphere by the sun's magnetic field and seen at the edge of the sun) and filaments (the same but superimposed over the solar surface where they look like dark curving arcs). These can change from day to day or be stable for weeks. Occasionally they vanish or appear over about 20 minutes! Plages or bright actively emitting areas can be seen near sun spots. Surface granulation can be seen but is more readily apparent at lower power then at high power. The larger sun spots can be seen and become more apparent if one "detunes" the filter out of the H alpha band. The NearStar is a compromise with its etalon sitting in the middle rather then at the front of the scope. As a result, only the central 0.5 degree of the FOV is in the H alpha band. I found that if you put the sun at the edge of the field of view the sun spots are more apparent, as you move the sun to the center of the FOV they dim or disappear. Twice, as a result of random chance, I was able to observe a solar flare. Each lasted for about 20 minutes. I've seen it described as "a crack in the surface of the sun" and having seen it I'd have to agree. It is brighter then any thing else. It is like you're peering into the sun's core. As the sun's appearance an change over as little as 15-30 minutes (prominences change shape, resolve, or rarely explode) it is more interesting to observe the sun in h alpha rather then white light.

              Recently I attended the Laurel Highlands Star Cruise (the star party of the AAAP) and met Jim Kendrick link to his store's site. I set up my 70mm NearStar next to his 50mm Solarview and compared the views as did about 15 people who stopped by when they saw what was going on. It was unanimous. The contrast was better in the smaller aperture Solarview and it gave much better views then the larger NearStar.  The SolarView 50 has less internal reflections. In the NearStar I often notice that the space around the sun is orange and not black. I assume this has to do with baffling or internal reflections. With the Solarview the space around the sun is black, surface detail was more apparent, and the prominences were more sharply defined.  It was I'd hoped for with the NearStar. Though the NearStar is an amazing and easy to use instrument, I'd been disappointed with its low contrast views. Though I'd learned to see a lot of subtle detail with it, it was sometimes hard for the novice to see what I was trying to show then at public star gazes. Now I have been able to obtain a Solarview of my own and it has become my new portable solar observatory. It fits in a small case with a TeleVue 1.25' diagonal and a Televue  8-24mm zoom eyepiece. It's set up is similar to that of the NearStar and is also easy to use. I've noticed that I can use more magnification with it then with the NearStar. Rarely could I use the 5mm with the NearStar, but I use it more and more with the Solarview.

              My video image galleries contain some B&W images made with a B&W video camera. These were shot with the NearStar. The Meade electronic eye piece with a infared filter on it is good for this purpose. You don't need a sensitive chip for solar work. The sun is plenty bright.

The earlier H-Alpha images in my videoastronomy galleries were all taken through the Coronado Instruments NearStar. The more recent ones were taken with the Solar view 50.