How to look at the Sun - safely!

by Suzanne Taylor, Science Programmer
May 2004

Why do I even want to view the Sun? The Sun is a fascinating place – and it’s constantly changing. Usually, there are visible sunspots that you can track across the Sun’s surface. During a solar eclipse you can see the shadow of the Moon pass in front of the Sun, blocking out its light and making the solar corona visible. Sometimes, the planets Mercury and Venus pass in front of, or transit, the Sun. From Earth it’s possible to watch them go by.

As a child, were you ever told, “DON’T look at the Sun or you’ll go BLIND”? Unlike other Mom-isms (remember the one, “If you make that face for long, it’ll stay that way!”) it actually IS true that looking at the Sun can be dangerous unless you take the proper precautions.

Here’s the golden rule:

Never, ever look directly at the Sun -- even during an eclipse or at sunrise or sunset. The Sun emits dangerous UV radiation that can permanently damage your eyes and even cause total blindness. This can happen in a matter of seconds. There are no nerves in the back of your eyes so you won’t be able to feel this damage as it occurs.

Now that we have that rant out of the way...

What are the safest ways to admire the Sun?

There are two safe ways to view the Sun: indirectly, by watching its projection, or directly, by protecting your eyes.

Indirectly: The Pinhole Projector

	The image of the Sun will actually be much smaller than what is shown here. The image projected on the board will have a size equal to approximately one one-hundredth the distance from the pinhole to the board.

One of the easiest (and least expensive) ways to indirectly view the Sun is with a pinhole projector. The projector basically acts as a camera. Here are a couple of different ways to create a pinhole projector:

• The easiest method is to get a piece of bristol board (or something similar that has some weight to it) and prick a tiny pinhole in the centre using a fine pin. (In order to create a really tiny hole, you may want to first cut a hole in the centre of the board, then cover this with aluminum foil and prick a hole in that.)
• Hold the board so that the Sun’s light can pass through the pinhole (but don’t look through the pinhole at the Sun – remember, you promised!) This is going to act as your lens. The Sun’s rays pass through this pinhole to form a circular image.
• Hold a second white sheet of Bristol board behind the first, and you’ll see a small dot of light. This isn’t just light coming through the pinhole – it’s an image of the Sun being projected onto the board. (Actually, it’s an inverted image of the Sun. Do you know why?)
• The further you hold the second board from the first, the larger the image of the Sun will appear, but the dimmer it will get, because you’re essentially spreading the same amount of light over a larger area.
• You can also create a pinhole viewer out of a box, but it needs to be fairly long to get an image of the Sun that is big enough to see. Make the pinhole at one end of the closed box, and create a hole in the side of the box near the opposite end so that you can see the projection of the Sun on the opposite side from the pinhole.

Look at your projected image of the Sun for any small dark spots; these are sunspots. Want to compare what you see with what the Sun looks like right now?

Indirectly: Telescope or Binocular Projection

	We used the projection method while monitoring sunspots at the Ontario Science Centre.

Another way to see a projection of the Sun is using a telescope or pair of binoculars.

• Point the telescope toward the Sun without looking through the eyepiece or finder telescope. (In fact, the finder scope should be capped.)
  
  OR
  
  Using binoculars, cover one of the lenses with a cap or piece of dark cardboard and some duct tape so that you are left with a single lens.
• Set up a piece of white board behind the eyepiece where the image of the Sun will be projected and move the telescope or binoculars until you see this image appear on the board.
• You might have to try different distances and angles, but do not get impatient and look through the lens!

Be careful. The Sun’s rays are very bright and hot, and when they come through the telescope and eyepiece they are being magnified by the lens. So to be safe, there shouldn’t be anything in the path of the Sun’s light coming from the eyepiece. Anything flammable, as well as your skin, can be burned by the Sun’s rays in seconds.

Directly: Glasses and Filters

	You can purchase welder's glasses with a #14 filter at the following stores in the GTA: Efston Science: The Science and Astronomy Superstore 3350 Dufferin, Toronto 416-787-4581 Vertex Welding Alloys & Equipment 7585 Torbram, Mississauga 905-671-2000 Praxair 8270 Sheppard Avenue East, Toronto 416-208-8200 Halladay Welding Supplies Ltd 250 Ferrier, Markham 416-499-0524

While projections of the Sun are a good way to safely view an eclipse or transit, sometimes it’s just not the same thing as looking directly at the Sun. It is possible to do this if you have a filter. The right filter will block enough of the Sun’s energy so that your eyes don’t get damaged. Eclipses, transits, and even some sunspots are visible by simply looking at the Sun unaided – but protected!

Welder’s glasses with a #14 filter work very well. (They’re also inexpensive.)

Be careful: there are many materials that may seem to block out the Sun’s rays, but which are not safe to use for solar viewing. DO NOT LOOK AT THE SUN THROUGH sunglasses, photographic neutral density filters, polarizing filters, photographic film, dark plastic such as garbage bags, or smoked glass.

Directly: A Filtered Telescope

Another way to directly look at the Sun is using a telescope with a proper solar filter attached to the end of it.

• These filters must be made specifically for this purpose – they're known as "solar filters". Other filters simply dim the Sun’s rays and will not protect your eyes from damage.
• The solar filter should fit over the end of your telescope, not over the eyepiece.
• Magnified light can be dangerous – it’s better to filter it before it even enters the telescope. Good solar filters are available from stores that sell telescopes and telescope accessories. There are also small portable devices called “sunspotters” which offer a projection of the Sun. By using a pinhole set-up and mirrors, the sunspotters intensify and spread the projected light to form the image.
• You can use a beginner’s telescope which can be used to view not only the Sun, but the vast multitudes of fascinating night sky objects that are out there just waiting to be discovered.

Have fun!

Now that you have a good idea of how to have a safe and fun time looking at the Sun, get out there and try some of these ideas out! But don’t forget the sunscreen…have I mentioned the dangers of UV rays on your skin?