We have two wonderful events involving the sun in the next few weeks – a solar eclipse on May 20 and the passage of Venus directly across the sun’s face on June 5. You’ll want to get ready for both by purchasing a simple, safe solar filter.
On Sunday afternoon and evening May 20, sky watchers living in a noodle-like strip from southern Oregon through western Texas will witness an annular (ring) eclipse of the sun. Because the moon will be just one day past apogee or farthest from Earth, it’s too small to completely cover the sun. Like a lid too small to cover the pot, a ring of sunlight remains around the silhouette of the new moon. Unlike a total solar eclipse, when you can safely view the sun without a filter for a few minutes during totality, you’ll need to protect your eyes throughout this eclipse.
If you live outside the approximately 150-mile wide noodle, don’t worry. Most of the U.S. and Canada will experience a partial eclipse except for the East Coast, where the sun will have already set. The sun will be 63% covered in my town of Duluth, Minn. and set while still in eclipse.
The second event is the transit or passage of Venus across the face of the sun happening during afternoon and evening hours on June 5 for the U.S. and Canada. Venus transits come in pairs – the last pair was in December 1874 and December 1882. The first of the current set began with a transit on June 8, 2004. If you miss the June 2012 event, you’re almost certain to be in your grave for the next transit in December 2117.
I’ll have much more information on each event in the coming days, but for now it’s important to prepare. Since both involve looking at the sun, you’ll need eye protection in the form of a SAFE solar filter. The sun emits dangerous infrared (heat) and UV radiation. While our skin can handle the effects outside of the occasional sunburn, our eyes cannot. If you still directly at the sun, you’ll fry your retinas and not even know it, since they lack pain receptors.
Special “eclipse glasses” or a #14 welder’s provide a safe and convenient way to view the sun. Both block 99.99% of the sun’s light and cost only a few dollars. My personal favorite are the eclipse glasses made with an optical-quality plastic called black polymer. They provide a sharp, pleasing image of the sun. Aluminized plastic filters made of mylar also work well. Welder’s glass gives a green solar image, mylar a blue one and black polymer a light orange.
Safe, screw-on solar filters are available for camera lenses if you’re thinking about taking pictures of the events. Or you can buy individual sheets of polymer or mylar and rubber-band them around your lens.
Telescope users can choose from a wide variety of mylar or glass filters mounted in caps that fit snugly over the objective lens.
Here are basic DOs and DON’Ts when it comes to safely observing the sun:
DO NOT use smoked glass, old photographic negatives, sunglasses or shiny mylar helium balloons to view the sun. They allow dangerous radiation to pass through to your eyes.
DO NOT stack lower numbered welder’s glasses to “create” a #14. Use #14 ONLY.
DO NOT put on eclipse glasses and look through an unfiltered telescope. They’ll melt and expose your eyes to concentrated sunlight in seconds!
DO NOT place solar filters over the eyepiece of a telescope. They’ll melt or crack in the concentrated sunlight. Place filters ONLY over the objective end of the scope.
And now for a few DOs:
DO observe the sun as long as you like through a safe filter.
DO wrap and secure a safe solar filter around each objective lens on the FRONT end of your binoculars for a crisp, magnified view of the sun.
DO build a simple pinhole projector to view the sun safely without a filter. Instructions HERE.
DO use optical projection to project a big, bright image of the sun from binoculars or telescope onto a sheet of white cardboard. Instructions HERE.
And now you need a SAFE solar filter. Below I’ve listed several websites where you can purchase one. You can also check online and in the yellow pages of the phone book for a local welding supply store and request a #14 welder’s glass.
* Thousand Oaks Optical — A large variety of solar filters for telescopes and cameras. Sheets of black polymer and other materials are available in several different sizes if you want to make your own.
* Rainbow Symphony — Eclipse glasses and solar viewers as well as filters for binoculars and telescopes. The most basic glasses are cheap at just 85 cents apiece, but you’ll need to purchase a minimum of 25 pairs. A mounted piece of #14 welder’s glass or coated optical glass costs $20.
* Opt Corp — Offers high-quality Baader mylar optical filter material. Cost: $35 for a 10-inch by 10-inch sheet.
* Orion Telescopes — Glass solar filters for telescopes and binoculars. Baader filter material available for 4.5″ telescopes.
* Amazon.com — Safe solar eclipse viewers for naked eye use
If for some reason you aren’t able to get a solar filter, all is not lost. The tiny spaces between leaves on a tree act like pinhole projectors and will cast hundreds of images of the sun on the ground below during the eclipse. To see the effect even better, bring along a white sheet or blanket and spread it out beneath the tree. You can even cross your hands over one another at right angle to create a pattern of small “holes” that will reveal the changing shape of the sun as the eclipse proceeds.