Observing the Sun can be done using one or several different types of filters. When observing the Sun, it is very important to use a filter that reduces the amount of visible light transmitted. This reduces, but does not completely eliminate, the risk of damage to your eyesight.
Most solar filters transmit less than 1/100th (1%) of the Sun’s light. This means that if you are looking at a 100-Watt incandescent bulb, it would appear as dim as a 1-Watt bulb.
Furthermore, most solar filters absorb or reflect away ultraviolet and infrared radiation meaning these filters do not permit observation of the sun and its sunspots using an ordinary photographic camera. Professional solar telescopes use cameras with special filters which protect their sensors, but require exposure times of several seconds.
Are sun filters for telescopes safe?
You can look at the sun through a telescope with the use of solar filters. Telescope sun filters are safe because the light transmitted though the filter is so dim compared to even a modest telescope, that you cannot see any “sun spots” or other surface features. Plus, there is an additional obstacle in your way: the secondary mirror inside your telescope. This acts like another filter by restricting the amount of light that reaches your eye.
If you view Sun through any optical device (e.g., telescope, binoculars or camera lens) is potentially very dangerous without a solar filter. Not only do filters greatly reduce the intensity of sunlight that reaches your eye, they also almost completely block harmful ultraviolet and infrared radiation.
What are solar filters?
Solar filters for telescopes and binoculars usually consist of a thin aluminized glass or plastic disk that fits into the telescope drawtube or eyepiece holder. These typically cost $100 or more. Often, filter disks are made from an special aluminized glass or bluish-white appearance. It is because they let through only a fraction of the visible light and almost no UV or infrared radiation.
Do not use any kind of neutral density (ND) filters, sunglasses, photographic neutral density filters, or smoked glass as a solar filter.
H-alpha (Hydrogen-Alpha) filters are the only safe filter for observing the Sun, as they transmit a specific frequency of light emitted by hydrogen atoms when they become ionized.
Safe Solar-Observing Techniques – How Can You Safely Observe the Sun
If you are looking for methods on how to see sun, you will notice that there are three possible techniques.
Solar filters – When viewing the sun with a telescope, be sure to use a filter that screws into the eyepiece holding clamp. Pointing your telescope for solar observing without a proper solar filter is very dangerous and can cause serious eye damage in seconds!
H-alpha filters are not safe for use with binoculars or unmounted telescopes because they are designed to fit over the eyepiece where they are held in place securely.
Solar Projection – Not as popular as other techniques; instead of putting a solar filter on your telescope’s end, you simply point it towards the Sun and project the light onto another surface like a wall or screen. This is not safe for telescopes without an eyepiece holder, but binoculars work well if equipped with standard Porro prisms (not roof prisms or Abbe-Koenig prisms). You can also use telephoto lenses for this technique.
Related: If you enjoy stargazing, be sure to check out our selection of telescopes, binoculars and star projectors for your home.
Personal Solar Telescope – Lastly, you can use a “Personal Solar Telescope” (PST). A PST is like a very long telephoto lens that attaches to your camera’s back and side by way of a special T-mount adapter. If the image on your camera’s sensor doesn’t fill up the frame, it is possible to attach multiple extension tubes to increase the magnification.
What features can you see on the Sun?
The Sun is a ball of incandescent gas. There are no ships or airplanes on the surface, nor can you see houses, trees, or any other objects.
Sunspots appear as dark patches (“black spots”) that can be seen with an ordinary telescope through a solar filter. They are caused by strong magnetic fields that inhibit the flow of heat from the Sun’s interior. Sunspots are regions where the Sun’s magnetic field is extremely strong, suppressing convection and restricting the upward transport of heat from below. In other words, sunspots are “cool” places on the surface of our star because energy is being efficiently transferred inwards and not outwards.
Solar flares and prominences – Active regions may be host to solar flares, which can impart a brief brightening (about 1 minute) of the Sun’s surface when viewed with the right equipment. In order to see solar flares with a telescope, you will need a specialized filter which passes only Hydrogen Alpha light. You might also see dark, snake-like filaments where higher-energy particles have escaped from the Sun. These can appear as a bright region near the limb of the Sun, or as a reddish loop.
Filaments are cooler clouds of gas suspended above the Sun’s surface by magnetic forces. They are the most prominent feature of the Sun’s inner structure that we can observe.