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Sunspots & Eclipses: How to Watch Sun Through Telescope

One thing you can do as a backyard astronomer is check out the surface of the Sun for sunspots, for Mercury passing by, or when there’s a solar eclipse. 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.

Important: NEVER LOOK AT THE SUN WITH YOUR NAKED EYES. This could cause you blindness in less than a second.

Can you see the Sun through a telescope?

Yes, you can view the Sun through a telescope providing it is fitted with a solar filter that reduces the Sun’s brightness to levels safe for you to observe its surface. Looking directly, even with a telescope, can cause lifetime damage to our eyes, including blindness.

The most popular time for watching the Sun through a telescope is during a solar eclipse…

Dates for solar eclipses

2021Dec 14Antarctica
South Atlantic
2021June 10New England sunrise event
Maritime Canada
2023Apr 20Indonesia
2023Oct 14All of Nth AmericaPartial
2024Apr 8United States
(Texas to Lake Ontario,
Quebec and
New Brunswick)
2024Apr 8All of Nth AmericaPartial
2025Mar 9Nova Scotia sunrise event
Source: timeanddate.com

The Sun is a large and highly visible daytime sky object. (I cover others in my article on the planets and stars that can be seen in the daytime, if you know where to look). With a proper solar filter fitted you can safely look through your telescope and observe sunspots on the Sun’s surface or watch the Sun during a solar eclipse event.

What’s safe For observing the sun

You must use safe methods to view the Sun.

Safe methods with a telescope

How to view the Sun…

  • 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. Like this one, at Orion Telescopes…
aperture solar filter
6 Orion Safety Film Solar Filter for Refle…

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The sun filter telescope method

How do I safely look at the Sun through telescope? Adding a solar film to the aperture of your telescope that filters out the Sun’s brightness by a factor of about 100,000 will give you the safe means for looking at the Sun and avoiding permanent damage to your eyes.

Aperture filters are available to fit small refractors, viewfinders, cameras, spotting scopes, as well as binoculars. 

  • For large Dobsonians, a good option is an aperture mask and solar filter rather than full-aperture.

About full-aperture telescope solar filters

Looking for answers, I discovered Terence Dickinson, who has authored several astronomy books (2 are listed in my recommended book list), talks about two main types of Sun lenses or filters for telescopes: glass and Mylar. There is a newer type as well made by Baader.

What are these Sun lenses 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.

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 types are the more expensive. But, these will give you get a near-true color image of the Sun. This compares to the Mylar type, which is 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.
Mylar type solar filter for observing the Sun through telescope
A Mylar type of solar filter for Sun observation through telescope
  • Baader Astro Solar Safety Film: Baader is another brand name of plastic film used for solar safety. The product is made in Germany by Baader Planetarium and is a newer (and possibly more popular) addition to the safe-solar filter options. With this filter the Sun will appear in real color, neutral white. It reduces the “intensity of solar radiation by 99.999%” [Source: AstroSolar]. You’ll find it used in Orion safe solar filters.

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.

Dust cap covering Dobsonian with a smaller cap that can be removed to attach a solar filter
Smaller cap on the front cap of a Dobsonian that can be removed to attach a solar filter

If your 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 your telescope, another method suggested is to project the sunlight through a telescope onto a white board.

It’s a cheaper way of examining the Sun’s surface with a backyard telescope, but solar projection carries the risk of looking through the telescope –. You must NOT look at the Sun through the telescope when using this method. It’s an absolute no-no.

If you have children with you, especially keep an eye on them to make sure they do not venture to look through the telescope at this case...

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 interferring 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 [Source: 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 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.

When watching the Sun through a telescope, you might see a sunspot or two…

Earth-sized sunspot on the Sun observed through telescope Nov 10, 2020 from Argentina
Earth-sized sunspot 2781 on the Sun, captured November 10, 2020, from Cordoba, Argentina

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…

YouTube video

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.

solar filters for binoculars at Orion
4.30 ID Set of Orion Binocular Solar Filters

This set of two glass solar filters with an inside diameter of 4.30 fit Orion 20×80 Ast… [More]

Price: $149.99
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Or, use welder glass inserts…

Looking through binoculars to observe the Sun

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.

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.

Info sources

  1. Dickinson, T. 2019. NightWatch: A Practical Guide to Viewing the Universe. (affiliate link) Firefly Books.