Solar Scopes and How They Work

To kick off our first Sun Party of 2018 (February 10th @ Noon at Main Street Books) we thought we’d answer a question we get a lot:

Should we really be staring at the Sun through a telescope?

This is a good point. The Sun is terribly dangerous to look at – even briefly. Case after case shows that purposely looking at the Sun is indeed a very bad idea.

In order to look at the Sun safely, an enormous amount of light needs to be blocked out. And that’s exactly what solar telescopes do.

There are two basic ways of looking at the Sun with a telescope; outfitting a regular telescope with a solar filter, or using a hydrogen alpha telescope (H-alpha for short): a special type of scope specifically designed to use on the Sun.

White Light Filters

If you have a telescope, you can buy a white light filter to outfit on the end of the tube so you can look safely at the Sun. White light filters have two major advantages over H-alpha scopes:

  1. They allow you to see sunspots.
  2. They are so much cheaper.

H-alpha scopes are amazing at allowing you see texture and prominences on the Sun and I would never downplay that – but a plain old white light filter gives you a better view of sunspots. They are also much cheaper. A nice, quality white light filter, like these, run as high as $180. Compare that to an H-alpha solar scope, which can easily get to be $1800. And that’s on the cheaper side. So you can see how a filter would be a great idea for the casual backyard astronomer. Check out the pictures below to get a rough idea of what the difference is.

These pictures were taken of the Venus Transit in 2012. All pictures were taken by Brent Sorensen. The first one (large on left) is through an H-alpha scope and you can see a hint of prominences on the bottom edges. Note how large they are in comparison to the planet Venus, which is much closer to Earth than the Sun. Even with a planet (almost) the size of Earth, those prominences are pretty large. This gives you an idea of how large they are in reality – solar prominences are often larger than our own planet! And an H-alpha telescope allows you to see them.

Now check out the right-on-top picture. This is also through an H-alpha telescope. You can see the texture of the Sun, with distinguished surface features as opposed to the picture below it.

If you look at the last picture (bottom right), this is through a normal telescope with a white light filter placed at the end of the tube. You cannot see prominences or texture, but you can see many more sunspots. And that’s what a white light filter is great for!

H-Alpha Telescope

A Hydrogen Alpha Telescope is designed specifically to look at the Sun. But after discussing how expansive they are, and with the common lack of quality for sunspot viewing, why would you ever purchase one? Well, maybe you are so independently wealthy that you ran out of yachts to buy. In which case, please consider donating to SUSF. Or, if you are an avid backyard astronomer, you might consider purchasing this type of scope with a lifetime’s worth of saved pennies. Advantages of an H-alpha scope:

  1. You see more fine detail.
  2. They are designed to look at the Sun.
  3. They’re useful for sidewalk astronomy.

Some of the higher end H-alpha scopes allow you to see sunspots, but the lower end ones are awful with sunspots. However, you do see more fine detail, texture, and prominences through H-alpha scopes.

Regular telescopes outfitted with white light filters get a lot hotter a lot faster than H-alpha scopes, so because this scope is specifically designed to view the Sun, most of them stay cool for long periods of time.

With the H-alpha scope, you can see more texture on the Sun, and prominences. Some of the higher end ones also allow you to see sunspots, but the lower end ones are just awful at showing spots.

What Not to Do

Lastly, we’ll leave you with a list of common things to avoid:

Never look at the Sun. It sounds easy to avoid, but when setting up a telescope, especially a rigged regular scope, it can be easy to want to treat the Sun like any other celestial body. You can’t look through the finder scope to find the Sun. You can’t use a bullseye if you have one. The best way to find the Sun, is to use the telescope’s shadow.

Don’t leave white light filtered telescopes on the Sun for too long. The tube can get very hot inside, melt the glue holding the secondary mirror which will then fall down and crack the primary mirror. If no one is looking through the scope, the scope should not be on the Sun. While I have not yet experienced overheating problems with an H-alpha telescope, I cap it when it’s not in use.

Lastly, never ever get “filters” that are for eyepieces. It is not safe to look at the Sun with an eyepiece filter.Your filter must go on the end of the telescope. A telescope collects and focuses light, and that can make the tube get hot very quickly. Block out 99.9% of the light before it gets into the telescope tube.

Solar-do-and-dontYou need a filter that fits on the end of the telescope. I recommend something sturdy like solar filter glass, but there are sheets you can place on the end of the telescope. Extra care has to be taken to prevent damage to the sheet as it can tear, get scratches, and pinholes pretty easily.

The Joy of Watching the Sun

Whatever telescope or filter you use, the joy of watching an active Sun is real. We see our own star every single day, but we almost never get to watch it. It can be an extremely moving experience for someone to see the Sun up close and personal and realize it has filaments and texture, giant prominences and sunspots.

The Sun changes every day. It never looks exactly the same twice in a row. If you look very closely through a solar telescope, you can see things moving, very slowly, like clouds.

And perhaps most impressive is this: Because the Sun is so close to us, it looks amazing in a telescope. But even after the invention and public dissemination of the telescope, no one, not even Astronomer Royals, had the equipment to truly see our star. Some astronomers literally went blind trying to study our host star, and we get to view it with a $180 solar filter and a semi-expensive H-alpha telescope.

This is why the Southern Utah Space Foundation raised funds in 2016 to buy a dedicated H-alpha telescope; because at the end of the day, it’s an expensive piece of equipment for the average Southern Utah household, but it’s a fantastic tool that can be used by anyone in the community to see the surface of our star. We get to see the Sun with the detail that only a fraction of the human beings who have ever lived on this planet have been able to view it.

So come look at the Sun with us!





– This article was written by Lee Ricci –




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