How to Safely Observe the Sun
Never look at the Sun without proper protective equipment. This is very serious! Looking at the Sun can cause permanent blindness.
Solar observation is the only dangerous activity that an amateur astronomer does. To be safe, you must use proper protective equipment. There are a number of options available to the amateur astronomer. These are the ONLY ones that the Astronomical League recommends.
Always check all of your filters BEFORE you look at the Sun to be sure there are no cracks or holes that could let unfiltered light through. Do this by looking at a bright sky, not near the sun. If you can see any light at all, you have a defective filter. This is important for eclipse glasses as well.
There are three options for safely observing the Sun for telescope users.
- A Hydrogen-Alpha Telescope. These telescopes not only filter the light to a safe level, but they also filter it to a very specific wavelength – Hydrogen-Alpha. This can be used to see detail on the surface of the sun such as flares and prominences. They enable you to see the chromosphere.
- A full aperture solar filter. This filters the light down to a safe level. You will be observing the photosphere and will be able to see sunspots.
- Off-axis solar filter. These filters allow the observer to safely observe the Sun but are not full aperture. They are less expensive, and can be positioned to miss the vanes inside the telescope that use used to support some secondary mirrors.
Solar filters are ALWAYS used on the objective lens (the end pointing towards the Sun).
Be sure to put the cover on your finder scope.
During daylight, never leave binoculars or a telescope unattended when others (especially children) are present.
There are two options for safely observing the Sun for binocular users.
- Purchase a pair of solar binoculars. The filters are built into the binoculars. They can only be used for observing the Sun.
- Purchase solar filters to use on the sky-facing lenses of the binoculars.
Eclipse glasses can be bought in many places. They are inexpensive and safe but be sure that you are buying them from a reputable dealer. They should be marked that they comply with ISO 12312-2 international safety standards. The Astronomical League Store sells quality eclipse glasses.
Eclipse glasses should ONLY be used like a pair of glasses. You wear them to directly protect your eyes (no magnification). They may be used on top of or under your prescription glasses, but nothing else.
Welders use heavily filtered glass to protect their eyes while welding. The type required for observing the Sun is darker than most welder’s glass. Welder’s glass is numbered. The higher the number, the more protection they provide. They will usually show you a green image of the Sun. (no magnification)
To safely observe the Sun, you need Shade Level 14 Welder’s Glass. This should be a single piece of glass. If you use two pieces of glass together, then you need to have a total Shade Level of 15. Three pieces would need a total Shade Level of 16.
This is the safest way to observe the Sun. You are NOT looking directly at the Sun, there is nothing to break, and it is very simple to use. Sunlight passes through a hole in a piece of poster board and is projected onto a second piece. You observe by looking at the image on the second board. For instructions on construction of a pin-hole projection system, click here.
No other filtering options should be used. They are NOT safe!