Fun with the sun

 

Sunspots of February 3, 2026

Okay, hold on a sec. Let me be perfectly clear: The sun is the most dangerous celestial orb in the sky, and I DO NOT want you to think that my title "Fun with the sun" means that you can treat the sun, er, lightly. NEVER look directly at the sun with your eyes, not even for an instant! 

You know that guy, Andrew Huberman, who says you should go outside immediately after waking up in the morning and look in the general direction of the sun to reset your sleep cycle?

DO NOT FOLLOW THAT ADVICE!

Make no mistake. The sun is no toy! And, sure, we have all accidently looked directly at the sun from time to time, giving us black spots in our vision for the next several minutes. Experiencing that once should be enough of a warning for you to NEVER DO THAT AGAIN! 

Sunglasses don't protect you, either. Do not be misled. Sunglasses were not made to let you gaze up at the sun. Not even during partial solar eclipses. Too much harmful radiation can still reach your eyes unless you're looking through #14 welder's glass or Baader safety film (the stuff used in those cardboard solar eclipse viewing glasses) that's designed for solar viewing.

Galileo frequently looked at the sun through smoked glass, and that didn't protect his eyes well enough, either. He went blind in his old age, most likely from his solar studies. 

But I'm not talking about that kind of eye damage. I'm not talking about the kind of eye damage that comes back to haunt you later in life. 

I'm talking about the right now and instant eye damage that comes from looking at the sun through optical equipment, like binoculars and telescopes, without proper solar filters.

You may recall sometime in your life experimenting with magnifying glasses and sunlight. You can light paper on fire using a magnifying glass and sunlight. Yes! And that's just a tiny little magnifier. If you can start a fire with a magnifying glass, maybe now you can imagine the kind of fire that you can start with a powerful telescope!

No kidding! The cone of sunlight that's brought into focus on your eye by an unfiltered telescope is like a blow torch. It will literally burn your eyeball out of its socket! 

Some amateur astronomers like to demonstrate the hazardous nature of the sun at public sun-gazing parties. It's very effective! They will aim an unfiltered telescope at the sun and hold a grape just above the eyepiece. When you see that grape cook instantly, it will teach you a lesson you'll never forget!

Unfortunately, in the light of day, you can't see the dangerous cone of light coming up out of the eyepiece. It's something that you must maintain awareness of at all times when viewing the sun. Do not leave young children unattended with a telescope out in the back yard when the sun is up. 

So having spoken of the dangers of solar viewing, let's get back to the fun part!

There are a couple of completely safe methods of using a telescope for solar viewing. Well, "completely safe" if you use extreme caution! 

The first method is called projection. You aim the telescope at the sun and put a white card several feet from the eyepiece. The sun's image, with all its sunspots, will be projected onto the card. Note that this leaves the dangerous blow torch exposed to the public. So, make sure to keep people and body parts away from the eyepiece at all times during solar projection. Also bear in mind that the sunlight passing through the telescope can cause extreme heating within the instrument. Parts can melt or crack and be destroyed. For this reason, only simple Newtonian reflectors and refractors should be used for projection of the sun's image. Do not use the projection method with catadioptric telescopes such as SCTs or Maksutovs.

Another safe way to view the sun through a telescope is by using a full-aperture solar filter. Remarkably, a thin sheet of Baader solar film that completely covers the front end of the telescope, is all you need. 

Baader solar film blocks more than 99% of the sun's radiation, making the eyepiece view perfectly safe. However, you must be careful with the Baader film. Inspect it before each use to make sure there are no pinholes in it. And you must attach the Baader film securely onto your telescope, so that it can't fall off or get blown off by a gust of wind.

I purchased a full-aperture solar filter for my 11-inch SCT. It cost around $150 US. The filter is comprised of a sheet of Baader solar film glued onto a metal cell that slides onto the front of the telescope tube. Three nylon screws secure the filter to the telescope.

This kind of solar filter produces what is called "white-light" solar viewing. The sun's visible wavelengths are seen through the eyepiece as a neutral white disk with dark sunspots, as seen in the photo at the top of this page. 

Solar prominences on the sun's limb cannot be seen with white-light filters. Those features require a different type of filter called a Hydrogen-alpha solar filter. Hydrogen-alpha solar filters are very expensive! Even a small 50 mm aperture Hydrogen-alpha telescope costs more than $1000 US. I have a Lunt 50 mm Hydrogen-alpha telescope, and I enjoy the views through the eyepiece, but I haven't figured out how to get decent pictures with it yet.

Whether you're using projection, a full-aperture white light filter, or the Hydrogen-alpha method of observing/imaging, the sun presents a unique challenge for aiming your telescope. For all other celestial targets, like the moon, planets, and deep-sky objects, you can safely search for them with a finder scope. But, as mentioned previously, you DO NOT want to aim your telescope at the sun by looking through your finder scope or sighting along the main optical tube! So, how do you do it?

Tele Vue's "Sol Searcher" is the most elegant solution. Normally, when you're aiming a telescope at a celestial object, you start by sighting along the telescope tube. When it looks like the telescope is aimed at the object, you next look into the finder scope and center the target with your crosshairs or illuminated reticle. But the Sol Searcher allows you to find the sun by turning your back on it!

The Sol Searcher consists of two opaque disks of about 1-3/8-inch diameter, spaced about 2 inches apart. Very simple. You could probably build one yourself, if you have the skills and the right tools and materials. But the Sol Searcher costs only $50 US. Why reinvent the wheel?

The sunward disk on the Sol Searcher has a 3/16-inch diameter hole, referred to in my picture above as the "pinhole" (although it is much larger than a pinhole). The sunward disk serves two purposes. First, it turns the sun into a tiny disk that is projected onto the Sol Searcher's rear disk. Second, the sunward disk casts a shadow onto the rear disk that improves contrast to see the sun's projected disk. The rear disk has a small translucent screen, representing the size of the field of view in a low-powered eyepiece. When the projected solar image falls onto that screen, the sun should be in the telescope's field of view. Genius!

There's another way to aim your telescope at the sun without looking at it, and I used that method for years, but it wasn't easy! This method is based on the assumption that when you look at your telescope's shadow on the ground, the telescope will be aimed precisely at the sun when your telescope's shadow is smallest and when the shadow of your telescope tube on the ground is a perfectly round disk. In practice, this method of aiming your telescope at the sun relies heavily on good luck! Some days, you can use this method and find the sun in your eyepiece quickly. And then on other days, you try your best to make your telescope's shadow the tiniest footprint, but when you look in the eyepiece, the sun is nowhere to be found. You might spend 10 minutes searching for the sun without success. It can be very frustrating. But the Sol Searcher, by comparison, is straightforward. When you get the sun's disk inside that translucent screen on your Sol Searcher, the sun is guaranteed to be in your telescope's eyepiece field of view. It removes all the time-consuming guesswork of searching for the sun. I think the Sol Searcher is worth every penny of its $50 price tag. 

Funny story about my Sol Searcher purchase.....

As I mentioned earlier, I have a Lunt 50 mm H-alpha telescope, which I use with a Celestron 4SE mount and tripod. Finding the sun with that setup without a solar finder was getting more and more difficult and frustrating. When I found out that Lunt sold the Sol Searcher finder, I immediately placed an order. Lunt is just across town from me in Tucson, AZ, so I chose "in-store pickup" as my delivery method.

For as long as I can remember, the word "Sol" as a name for the sun has been pronounced "SAUL" (rhymes with "PAUL"). You'll recall that a day on Mars is referred to as a "sol." NASA videos talk about how many "sols" (which they pronounced "SAULS") a certain rover has spent on the surface of Mars. So, when I saw that Lunt was selling a "Sol Searcher," I thought it was pronounced "SAUL Searcher." As a finder scope that's designed only for the sun, it was quite natural for me to think of the pronunciation as "SAUL Searcher." And Goodness knows, I've spent many an hour searching for the sun in plain sight with my telescope, without success!

Imagine my surprise when I got a call one day from Lunt, informing me that my Sol Searcher was ready for pickup. I wasn't available when they called, so I got a voice mail. When I listened to the message, it went, "Hi, John. This is [so-and-so] at Lunt Solar Systems. I'm just calling to let you know that your "Soul Searcher" is ready for pickup."

Soul Searcher?!!!

Never once did I ever think of "soul searching" when I saw the name "Sol Searcher"! I laughed out loud at the pronunciation. And then I kicked myself for never having recognized the pun.

Wow! Okay. Back to the original topic of this post: Fun with the sun!

When using a white light solar filter, fun with the sun is limited to three activities: observing sunspots, solar eclipses, and transits. Let's discuss these for a minute.

Partial solar eclipse of October 23, 2014

Solar eclipses over your back yard are extremely rare! You might witness a couple of partial solar eclipses in your lifetime, if you're lucky. You can increase your chances of seeing a partial solar eclipse if you pay attention to the news and travel to a location where the eclipse can be seen. But if you're waiting on a local one that you don't have to leave home to see, then you're in for a long wait. Possibly decades.

Transits are even more rare! There are two types of transits: Venus transits and Mercury transits. They occur because Venus and Mercury are the only two inner planets. On rare occasions, Venus and Mercury can pass exactly between earth and sun, so that we see their silhouettes against the solar disk. Mercury is quite small, so you need a telescope to see it. Venus is large enough to see with your naked eye (and solar filter, of course), but it's a more pleasing view with a telescope. Not that it matters. We won't see another one in our lifetimes.

Mercury transit on November 11, 2019

Of the two types, Mercury transits occur more frequently because of Mercury's great speed. It orbits the sun much faster than Venus, creating more opportunities for a transit than Venus does. We could see as many as 13 Mercury transits in a century. But Venus transits happen less than once in a hundred years! They come in pairs, four years apart, and then take more than a hundred years to occur again. The last Venus transits came in 2008 and 2012. The next ones won't be until 2117.

Venus transit on June 5, 2012

Since eclipses and transits are so rare, fun with the sun using white light filters is usually restricted to viewing sunspots. Sunspots are interesting because they change slightly from day to day. The sun rotates counterclockwise on its axis, causing sunspots to appear on the left (east) side and drift westward a little bit each day. It takes 25 days for one solar rotation. Additionally, sunspots are known to follow an 11-year pattern of sunspot minimum (very few if any sunspots) to sunspot maximum (when sunspots are visible nearly every day). We're just past maximum, so we'll see fewer and fewer sunspots during the next several years until we reach minimum. The next maximum will be around 2034.

I guess what I'm trying to tell you is that the time to have fun with the sun is NOW!