How to safely view the upcoming solar eclipse and transit of Venus

Safe solar filters for looking at the sun come in several different varieties. Read down to learn more about each kind. Photo: Bob King

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.

Observers inside the band bounded by the blue lines will see the May 20 annular solar eclipse. The red line shows the even narrower strip where the moon will be perfectly centered on the sun. Click map to go to the interactive version. Credit: Fred Espenek / NASA

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.

Annular eclipse of Oct. 3, 2005. Credit: Sancho_Panza

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.

Transit of Venus on June 8, 2004 photographed through a small telescope. Venus will also be visible in binoculars and with the naked eye with a suitable solar filter. Click photo to go to my blog devoted to the Venus transit. Photo: Bob King

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.

You can mount binoculars on a tripod, cover one lens with a lenscap and project the sun's image safely onto a sheet of white cardboard. Photo: Bob King

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

Tiny gaps along the length of this palm frond created a series of solar crescents during the July 1991 eclipse. Photo: Bob King

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.

15 thoughts on “How to safely view the upcoming solar eclipse and transit of Venus

  1. Hi Bob, Just wondering if you can tell me a little more about the solar storm that is happening at this moment….Aparently it is quite big and could cause blackouts in may cities?

    • Bobbi,
      It’s a large spot group but no storms yet, just the possibility. We’ve had some large X-class flares and storms this year already from other big sunspot groups – pretty typical as we approach solar maximum next year – but so far there have been no power blackouts. I’ll be posting on this one later today.

  2. sorry this is what the article actually said!
    “A major sunspot group came into view today. The group will rotate to face us over the next week and is in the prime latitude to give powerful Earth-directed flares. It’s very active on this region.”

  3. Bob,

    This is a whole new area of astronomy for me, and I’m thinking about getting an RG-film filter for my Celestron SC 8. I see on some sites that while I will be able to see sunspots and surface texture (as well as Venus, of course!), to see prominence and flares, I’ll need an H-alpha filter.

    Can I buy this to use with the RG-film filter to get the same result as buying a dedicated H-Alpha filter package?

    http://www.amazon.com/1-25-Orion-H-Alpha-Extra-Narrowband-Filter/dp/B000YGGNDS

    Thanks for any advice!

    • Hi John,
      You’re right – you’ll need an H-alpha filter system to see prominences and solar flares. The link you provided to the screw-on H-a filter however is not the type used for sun viewing. That H-a filter is only for long-time-exposure photography of faint nebulas. It filters out everything but the dim, red light of hydrogen alpha emission from these objects – nighttime use only. A solar H-a filter is an elaborately built affair with multiple blocking filters made of quartz. A second glass energy-rejecting-filter is used over the objective to reduce the incoming heat load. Unfortunately a solar H-a setup for your scope cost around $2000. Small, dedicated solar H-a scopes are available for around for around $600.

      • Where can i buy H-alpha solar filters in WA state without ordering?
        And how much are they?
        With a Orion glass solar filter can i see solar flares and promenences?
        where can I buy eclipse glasses in WA State without ordering?
        I’ve always wanted to see solar flars

        • Hi Parker,
          You’ll probably need to order and H-alpha solar filter if you’re in WA. state since they’re an expensive specialty item. You might want to check and see if you have any local stores (perhaps a camera store) has a telescope company connection. Then they can order for you. The Orion glass filter will only let you see sunspots not flares and prominences. It’s a “visible light” filter and not a narrow-wavelength H-alpha variety. A typical H-alpha filter costs around $1000 and up. I don’t know where you can buy eclipse glasses in Washington. Maybe another reader might. You can order them from rainbowsymphony.com

    • Frank,
      Yes, it would be wise. If the end of the eclipse is near sunset you can remove the filter but of course avoid looking at the sun through the camera. Have you tried a test run? If your camera can be dialed down to a very low ISO like 50, lens stopped down to f/22 and exposure at 1/8000 second or shorter, you might not need a filter.

    • Lloyd,
      Don’t do it. Pop tart and other materials like the shiny silver balloons made of mylar are unsafe. While similar in appearance, they’re not made with the UV and IR blocking ability of real solar filter material.

  4. Hi Bob,
    I have a 5.2 inch reflecting telescope. i want to mount baader astrosolar filter on telescope cap. my telescope cap has a small hole and its aperture is 1.8 inch. what’s the safest way to mount it?

    • Hi Hamed,
      You could use strong tape and tape a piece of Baader filter to the inside or outside of the cap over the 1.8-inch hole. You could also mount a piece of the filter material between two pieces of cut-out cardboard and tape the the mounted filter to the inside or outside of the hole. If you’re observing the sun for a long time, check the taping every so often to make sure it’s still holding everything in place.

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