One of the things you can do as a backyard astronomer is check out the surface of the Sun for sunspots, for Mercury passing by or to view solar eclipses. But you must do so safely. NEVER LOOK AT THE SUN WITH YOUR NAKED EYES. This could cause you blindness in less than a second. Here I cover the ins and outs of looking at the sun with a telescope and how to do it safely as a backyard astronomy enthusiast.
Can you see the Sun through a telescope?
Yes, solar telescope filters provide a safe way of viewing the Sun with a telescope. They reduce the sun’s brightness to safe levels so you can observe the Sun’s surface for sunspots and during a solar eclipse. You should never look at the sun through a telescope without sun filters for any length of time as you risk damaging your eyes including blindness.
What’s safe For observing the sun
How to view sun…
Safe methods with a telescope
- use a telescope solar filter, which goes on the front of the telescope to intercept the Sun’s light and reduce brightness to a safe level, lessening it by roughly 100,000 times.
The sun filter telescope method
Wanting a safe way to look at sun through telescope? One chief approach is to use solar filters on your telescope to filter out the brightness. Full-aperture filters are perfect for this and fit small refractors, viewfinders, cameras, spotting scopes, and binoculars.
For large Dobsonians, a good option is an aperture mask and solar filter rather than full-aperture.
You might want to steer away from solar filters that fit onto an eyepiece which some telescopes or accessory kits come (more on that below).
About full-aperture telescope solar filters
What are these Sun lens or filters made of and what color? How expensive are they? These are questions that came to mind when I first learned of filters to allow me to look directly at the sun through a telescope.
Looking for answers, I discovered Terence Dickinson, author of numerous astronomy books, talks about two main types of Sun lens or filters for telescopes: glass and Mylar.
full-aperture sun lens for telescope types
The glass filter is glass with a special optical coating and the Mylar is a highly reflective polyester film.
Glass: The glass type are the more expensive. But, these will give you get a near-true color image of the Sun. This compares to the Mylar type that are likely to give a white or a blue tinged image of the sun seen through telescope.
Mylar: Mylar is the brand name of film of stretched polyester made from biaxially-oriented polyethylene terephthalate (thanks going to Thoughtco for this info). It’s that shiny reflective stuff of helium balloons, space blankets, and insulators.
About eyepiece solar filters
The smaller eyepiece solar filters attach to either end of a telescope eyepiece. The downside of using these is that heat from the Sun concentrates where you are focusing. According to Dickinson, these type tend to disintegrate with the heat generated by the Sun’s radiation, either melting or cracking, and this is concerning as it can do real harm to your eyes.
About Dobsonian solar filters
Large Dobsonians have large apertures and so it makes sense to mask the aperture to allow a smaller solar filter do the work. The front cap for the Dobsonian serves as the mask and has a smaller opening in it to attach the solar filter. Check out your front cap of your Dobsonian and you may find this configuration. You then need to get one to fit that opening.
If you cap is not like this, look for a commercial one to fit or you could make a DIY one similar to suit (see below).
How to use solar filter on telescope
A full-aperture telescope sun filter is a popular choice for safely observing the Sun.
These Sun lenses attach to your telescope, but unlike the moon filters that you add to the telescope eyepiece, you add a full-aperture solar filter to the front of the telescope. The entire aperture is covered.
What happens when you look at the sun through a filtered telescope?
The image you’ll see of the Sun when looking through a filtered telescope will be close-to-true color with the glass type solar lens attached. If using the Mylar type solar filters for telescopes you’ll probably see the image of the Sun as white or with a bluish tint.
Through a glass solar lens telescope set up, you’ll get to see a yellow-orange disc. And, you may see dark spots that are sunspots.
Indirect method of Watching Sun from telescope
How can you safely observe the sun with a telescope, otherwise?
Rather than a sun filter for telescope, another method suggested is to project the sunlight through a telescope onto a white board. While this solar projection is a cheaper way of examining the Sun’s surface with a backyard telescope, care is needed to avoid actually looking through the telescope. This is an absolute no-no. If you have children with you, keep an eye on them that they do not venture to do this.
how to look at the sun using projection
While a big advantage of using this method is that multiple viewers can observe the Sun at once using the telescope, the downside is that you’ll see less detail than when using a sun filter telescope approach. You will also need to cover the finder scope to stop it interfering because of its image projection and the worst part is the heat from the sunlight will harm your telescope optics as it enters and moves through the instrument rather than being filtered before entry. Hence this approach is not the best and telescope manufacturers warn against it (e.g. Skywatcher).
You may also feel inclined to look through the telescope when aiming it at the Sun. But you must resist and instead use the shadow of the telescope to align the scope and set it in place when the scope makes the smallest shadow on the ground.
In terms of using a telescope, hold a projection card a short way (say 1-2 feet) from the eyepiece. A refractor compared to a reflector is a better option for this method. The smaller type, less than 60 mm, is best, as any bigger may limit the effect due to heating of the instrument and surrounding air by the Sun’s radiation.
If you have a 70 mm, you can address this by using a cardboard cut-out to reduce the diameter of the aperture.
things never to do when Observing the Sun
- Never look directly at the Sun (this will result in permanent eye damage)
- Use a proper solar filter for viewing the Sun through a telescope or binoculars
- Make sure to place the dust cover over the finder scope to protect it from the Sun’s radiation
- Never use an eyepiece solar lens or solar filter material placed on the eyepiece end of the optical instrument. Solar intensity needs to be reduced before it enters the optical system of the instrument. This applies to both telescopes and binoculars
- It’s not recommended that you use your telescope to project sunlight onto another surface as the heat that builds up internally can damage the optics.
Things to see in solar observations
So what can you see safely of the sun through a telescope with a sun filter? You should see a sunspot as anyone with average eyesight should.
Watch sun through telescope, you might see a sunspot or two…
About sunspots: These are the cooler areas of the Sun’s surface and an average one is at least the size of Earth but they can be 10x that or more. Sunspots exist of two parts: a black interior (umbra) and a grayish zone around this called the penumbra.
DIY solar filter for telescope
For a DIY sunspot viewer…
You can make your own filter for a homemade solar filter telescope system. Baader solar safety film is popular and with things like a small cardboard box or matte black poster paper and tape you can fashion your own DIY solar filter for your telescope, or for your astronomy binoculars.
A homemade solar filter telescope instruction (video)
Making your own solar viewer filter…Here’s a video showing you how to make a DIY solar filter for telescope…
Using binoculars for observing the sun
You will need properly filtered binoculars to view the Sun. Just the same as the telescope you can add solar filters including making your own using solar safety film as mentioned above. Or use welder glass inserts…
A DIY sun filter for Binoculars
Direct Sun viewing with welder’s glasses that have suitable filters is possible. You can be a sun viewer this way as Dickinson suggests, getting a No. 14 welders’ plate from a welding supply outlet. You can tape the material over the binocular lenses – but definitely do not put it at the eyepiece end as this approach is unsafe.
Looking at sun through telescope without filter
No way should you look at the Sun through a telescope without using an appropriate solar safe filter. Doing so is a huge no-no and will cause permanent damage to your eyes.
Dickinson, T. 2019. NightWatch: A Practical Guide to Viewing the Universe. Firefly Books.