Sunday, October 2, 2016

The Big Eclipse - Part 2: Viewing Safely

I was going to devote this post to a discussion about what to bring to the eclipse, but I realized that I can't really talk about what to bring until I've discussed viewing safety and the items you'll want to have for that.

First and foremost: never look directly at the sun (except during totality).  Don't look at it using your naked eyes, don't look at it through an unfiltered telescope or binoculars, don't look at it through an unfiltered camera.  The sun is no more dangerous to look at during an eclipse than normal, but people are more tempted to do so during an eclipse.  The only exception to this is during those few minutes or seconds of actual totality when the entire surface of the sun is blocked by the moon.  Even a very deep partial eclipse is not safe to look at.

However, the partial phases of a solar eclipse are really interesting too, seeing the outline of the moon creep slowly across the sun's surface.  So what can you do to view it safely?  Fortunately there are many options.  The easiest and safest is to use pinhole projection.  Basically you're building a simple pinhole camera.    Of course anything with small holes will work.  I've seen people use saltine crackers, and I've used my straw hat.

I'd recommend using a cardboard box with one side removed and a pinhole in a piece of foil at one end.  Here's a good link that describes how to build one:

Another safe way to view with slightly better image quality is to use a pair of binoculars to project the image of the sun onto a light colored surface.  Again, do not look through the binoculars.  Leave the lens cap on one side of the binoculars and aim at the sun with the eyepiece pointed at a light colored surface a few feet away.  You may need to adjust the distance between the binoculars and the surface to achieve good focus.

If you want to look directly at the sun, you'll need a safe filter.  Examples of safe filters include #14 welder's glass and aluminized glass or mylar filters specifically designed for solar observing.  Do not use sunglasses, film negatives, smoked glass, or neutral density filters.  Do not use space blankets or other aluminized mylar not specifically manufactured for solar viewing.

Safe solar filters come in several forms.  There are the cardboard "eclipse glasses" for naked eye viewing that are available from many online sources.  I strongly recommend that you buy a few of these regardless of what else you get.  They are relatively inexpensive and it's really cool to see the partial phases of the eclipse directly using those glasses.  Just Google "eclipse glasses" to see your purchasing options.  If you're local, I have quite a few extras that I'm happy to share.

If you want to try photographing the eclipse (the subject of a future post) or viewing through a telescope or binoculars, you'll also need a solar filter that fits snugly over the end of the camera lens, telescope, or binoculars.  There are many suppliers for these filters, but I like Oceanside Photo and Telescope:  Look for a filter that is slightly larger than the outside diameter of your lens or telescope.  You may need to add some foam tape to the inside of the filter for a snug fit.

If you have specific questions or want help choosing a filter, please feel free to contact me.

This is really just a summary, and an excellent article on safe viewing can be found here: and I'd strongly urge you to read it.

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