Learn how to see the solar disk worry-free, whether it's during an eclipse or on an ordinary sunny day.
For special events such as solar eclipses, I always choose my words very carefully when advising people on how to safely view the Sun. I want people to enjoy the beauty, but on the other hand, there’s a natural tendency to be overly cautious. After all, I don’t want anyone to suffer eye damage.The problem with observing the Sun is obvious: it’s so bright that prolonged, direct exposure can cause permanent damage to the retina, leading to loss of vision or blindness. To observe the Sun safely, you need to filter out more than 99% of the Sun’s light before it reaches your eyes.
Given these caveats, here’s some practical advice on how to safely observe sunspots and solar eclipses alike. This article covers a wide range of options:
- Viewing an Eclipse Directly
- Projecting an Image of the Sun
- Using a Telescope or Binoculars
- High-End Filters for Telescopes
Alternatively, you can go to a welding-supply store and buy a piece of #14 arcwelder’s glass, which reduces sunlight enough for safe direct naked-eye viewing. And it’s important to remember that the annular and partial phases of the May 20th eclipse will be easily visible to the naked eye. In fact, even Venus’s disk will be large enough to see without optical aid during the transit, although I would certainly recommend binoculars or telescopes for the most interesting periods at the beginning (ingress) and end (egress).
But no matter what, do not use “filters” such as smoked glass, stacked sunglasses, polarized filters, camera filters, candy wrappers, or compact discs. They might reduce the Sun’s glare, but enough harmful radiation can sneak through to damage your eyes. Only use materials specifically manufactured for safe solar viewing, or #14 arcwelders glass.
If you’re still queasy about using filters, or if you want to show the Sun to many people at the same time, you can use a small telescope or binoculars to project an image of the Sun onto a screen or white sheet of paper (almost any flat surface will suffice). A big telescope lets in a lot of sunlight, which poses the risk of overheating internal components. So I recommend either using a telescope with an aperture no larger than 4 inches, or using a mask with a 3- to 4-inch-wide hole to block the opening of any telescope with an aperture greater than 4 inches.
Remove the finderscope and place an eyepiece at the telescope’s focuser. Aim the telescope in the general direction of the Sun (without looking at the Sun through the telescope!) and move it around until sunlight streams out of the eyepiece. Believe me, you’ll know when you hit the sweet spot. You can also use binoculars mounted on a camera tripod, but make sure to cover one lens. A sunshade that blocks ambient light from falling on the projection surface will improve your view.
If you want to observe the Sun through a telescope, there are many options. Because binoculars and telescopes concentrate the Sun’s blazing light, it’s even more crucial to use safe filters. Make sure to avoid any filter that is placed at the eyepiece end of the scope. The concentrated sunlight will probably destroy such a filter, followed shortly thereafter by your vision.
The easiest and least expensive option is solar filter material from a company such as Baader, whose material has been highly rated in an S&T Test Report.
Make sure to place the filter material at the front end of your telescope, and to cover the entire opening. If you plan to use a large telescope, no problem — simply create a mask with a 3- or 4-inch-wide hole and cover the hole with your filter material.Many different companies sell safe solar filters (often made of glass, plastic, or Mylar) that go on the front end of scopes, where they block more than 99% of sunlight before it ever enters the telescope tube. These filters allow you to gaze at the Sun for hours with no risk whatsoever, and are basically showing you the Sun’s visible surface (the photosphere) in white light. Besides seeing the eclipsed Sun or Venus’s silhouette, you will probably see scads of sunspots as well, which are fascinating in their own right.
Make sure your filter is securely attached to the front of the scope, so there is zero possibility that it will come off while viewing. And to avoid damaging your finderscope, either remove it or place a cap or solar filter at its front end. Also note that safe solar filters work equally well with binoculars.
I wish you safe viewing of the Sun, and most of all, clear skies! After all, even sunlight can’t poke through heavy clouds in Earth’s atmosphere --- the ultimate natural solar filter.
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