Eclipse News

Viewing the Total Eclipse: Direct Methods

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In our last post we took a look at methods to project an image of the sun and observing it indirectly.  These options are the safest for viewing the sun and lend themselves well to group observation.  The majority of eclipse chasers, however, will use films and glasses specifically designed for safe direct solar observation.

Direct Viewing No-No’s

In speaking with eclipse enthusiasts at the booth there appears to be some misconceptions regarding safety when directly viewing the sun.  The following list are methods for viewing or photographing that are NOT SAFE and should not be used.

  • Sunglasses – ALL
  • Neutral Density or Polarizing Filters – for camera lenses
  • Eyepiece Filters – filter sunlight before it enters the scope
  • Exposed Film – some with silver may work, don’t risk it
  • Welder’s Glass – good only if #14 or greater

I have even had a few people try to tell me they routinely stare at the sun with no protection at all.  I don’t believe them, they could still see me.

ISO Standard 12312-2:2015 applies to “all afocal (plano power) devices intended for direct observation of the sun” and specifically lists devices and products that are not safe for direct solar viewing.

In My Finest Polyester

The class of polymers known as polyesters have become indispensable to our daily lives.  Polyesters are incorporated into our clothing, bed sheets, furniture, food packaging; it has applications in science, graphic arts, and marine / aviation products; it is an integral material in compact discs, recording tapes, balloons, nail polish, sails, space suits, bottles….the list goes on and on.  I am hopeful they no longer manufacture the powder blue polyester suit my mom used to make me wear.

The most popular polyester is polyethelene terephthalate (PET) which, when the polymer fibers are biaxially-oriented (BoPET), can be stretched into thin films.  To avoid any further chemical tongue twisters we will refer to the film by its most common trade name Mylar.  When Mylar film is coated with aluminum or other metals it transforms into a very effective solar safety film, blocking 100% of harmful UV and infrared radiation as well as 99.9% of the sun’s visible light.  Mylar and more recent films (Black Polymer, AstroSolar™ Film by Baader Planetarium) typically allow passage of only 1/100,000th of our star’s radiation to your optical device, be it a camera lens, telescope or your eye.​

Since holding a sheet of film in front of your eye or camera lens is not only impractical but quite uncomfortable, these films need to be fit and mounted for various sized devices.  Enterprising solar observers have populated the internet with DIY solutions for mounting solar film on cardboard tubes, card stock, PVC pipe, even the plastic lid from your peanut butter.  The only requirement is the filter fit snugly around the outside diameter of your binoculars or telescope – don’t forget your finderscope – so an accurate measurement of the sunward end of the tube is your first step.  Here are a couple of websites that detail the construction of various solar filters:

Simple Posterboard Filter

Plastic Lid Filter

Other Approaches

 

It’s Alive!

Our sun is basically a big ball of hydrogen, continually converting it’s mass to helium and emitting a tremendous amount of energy in the process.  Lucky for us it has a few billion years worth of hydrogen to burn through before life on earth is in serious trouble.  When hydrogen in the sun’s lower atmosphere is “excited” in the balmy 30,000° F + temperature, the atom absorbs that energy and then releases (emits) it at a specific wavelength.  Although hydrogen emits at several wavelengths, it is its emission line in the red part of the spectrum at 656 nm (nm = nanometer = 1/billionth of a meter) that is of interest to solar observers.

The various films described above allow light (not much of it, as we discovered) from across the visible spectrum through to your eye while blocking harmful UV and infrared.  Depending on the film this produces a static view of the sun in “white light”, although the sun will appear bluish (mylar) or yellow-orange (black polymer-AstroSolar™ films) through them.  Sunspots are easily visible when using these filters.

The view through hydrogen-alpha (the 656 nm emission line) filters and telescopes reveal our sun as an active, churning ball of gas.  Flares and prominences erupt from the sun’s edge and dark filaments and bright spots move across a now grainy, bubbling surface.  The view through a H-alpha scope is quite spectacular.

Filters and telescopes that isolate hydrogen at 656 nm (all other wavelengths are blocked) are pricey, but if you find yourself next to Mr. Geek and his solar scope on August 21st, muscle in for a look-see.

Sky & Telescope Article on H-Alpha

 

At first flash of Eden,

We race down to the sea,

Standing there on Freedom’s shore,

Waiting for the sun.

The Doors, “Waiting for the Sun”, Morrison Hotel, 1970

© Nipper Music / Doors Music / ASCAP

 

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