Looking at the Sun directly is dangerous: it will damage your eyes. You need to use approved optical systems to view the Sun, both with and without telescopes or binoculars. I highly recommend that you work with a local astronomer or a local astronomy club to get set up with the equipment you need in order to do the kind of observing you wish.
In brief, all optical systems, like telescopes, binoculars, monoculars, spotting scopes, and the like, require that you place a solar filter in FRONT of the system’s light collecting opening (the objective). You do not want unfiltered sunlight to enter your optics, as this will likely damage your optics as well as your eyes. Some small refractor telescopes can be used to project unfiltered sunlight onto a white board. DO not do this with large telescopes or with reflector telescopes or catadioptrics.
- Use certified solar filters. Companies like Baader (https://www.baader-planetarium.com/en/solar-observation.html) make excellent solar film for covering telescope optics.
- Make sure that the filters cover the front of your telescope’s system, the opening where the light goes in.
- Make sure that the filters cannot come loose and fall off the telescope when in use. Tape the filters on for protection!
- Ask for help from someone who has done this before. Better safe than blind.
Project the sun’s image onto white paper or board, but only with a SMALL refractor. This can damage larger telescopes, like SCTs and such. When in doubt – don’t.
- Use Welders Filters shades 13 or 14. While #12 is also safe, it is not too comfortable. These can be placed in front of your eyes when looking directly at the sun. These are not for use with a telescope or other optical aids.
- DO NOT Use random glass filters or lenses that have been marked as solar filters. Many are not safe! This includes stacking old exposed film.
- DO NOT Place filters at the eyepiece of the optical system: they will burn and break!
- DO NOT Expect solar glasses to protect you from harm when using them with binoculars. They will burn and you will be hurt!
- DO NOT Use skin sunscreen in your eyes. This does not work. Yes, people have done this. Don’t.
Sky & Telescope Safe Solar Observing
The orbit of the planets around their corresponding sun is elliptical in shape. The other interesting thing about this arrangement is that the sun will be at one of the ellipse’s foci, meaning, that at one point in the orbit, the planet will be further away from the sun than at other times of its year. Our Earth follows these same rules with our star, the Sun. The vocabulary here is helpful…. Aphelion is when the planet is furthest from the Sun, while Perihelion is when the planet is at its closest approach to the Sun.
The Earth’s Aphelion takes place in the early portion of January, while perihelion takes place in early July. The dates change a little back and forth with things like leap years and such. Yep – the calendar is a quirky thing. At the 2019 aphelion the Earth was 94,513,221 miles from the Sun (July 4th 2019). At the 2019 perihelion on January 3rd, the Earth was 91,403,554 miles from the Sun… those changes are very small, so small in fact that the two foci of the Earth’s elliptical orbit are within the diameter of the Sun!
With the distance changing between the Earth and the Sun, will the Sun appear to change in size over the course of the year? The answer is a clear “YES”! In fact, anyone with modest camera equipment and a safe solar filter can prove this out easily enough. How?
- Get a camera you can use with the same lens throughout the year.
- The lens should have a reasonable, long focal length… 200-500mm. The longer the focal length is, the more easily the Sun’s apparent diameter change will be to see.
- Cover the lens with a safe, approved solar filter. I recommend Baader Solar Film. WARNING!! Do NOT mess around with this, as a failure to use proper filtration will damage your camera and your eyes permanently!
- Mount the camera on a tripod for stability.
- Take photos of the Sun on clear days throughout the year.
- You can then overlay the images using editing applications to see and measure these changes.
I took these images below using a Nikon D-810a, a 300mm telephoto lens and a Baader Solar Film filter. The image on the left was on aphelion July 7, 2018. The image on the right was taken during perihelion on January 3, 2019. I had to run around a little to find the correct lens but managed to get it right! Take notes. That helps! The apparent diameters of the Sun are obviously different in the two images… and, if you do the math, the change is just a little bit more than 3%.