Viewing the Eclipse
DO NOT LOOK DIRECTLY AT THE SUN WITHOUT PROPER EYE PROTECTION
DO NOT LOOK AT THE SUN THROUGH BINOCULARS, TELESCOPE OR CAMERA
DO NOT "STARE" (LOOK FOR MORE THAN A FEW SECONDS) AT THE SUN
Eclipse viewers are made according to international safety standards - they must block 99.997% of visible and UV radiation, and 97% of the infrared
They are safe for direct viewing of the Sun, and relatively cheap (under US50c each, excluding shipping, if bought in bulk).
They can easily be shared - people should be looking for only a few seconds at a time.
Current suppliers include:
It is also possible to buy filter material, and print+assemble your own (in bulk) - see this page
Alternative Eye Protection
A double layer of Five Roses teabag foil wrapper.
Three layers of "space blanket", used by first-aiders.
Shade 13 or 14 welding glass is quality-controlled to meet the required safety standards for eclipse viewing.
Ordinary sunglasses are not suitable
for eclipse-viewing - they block only about half the sunlight (eclipse-viewers block 99.997%).
Some commonly available foil materials have filtering properties similar to those of recommended solar filter material - they block visible, UV and infrared.
Transmission measurements of some that I made while at the Johannesburg Planetarium are available here
Obviously, these materials are not the ideal substitute for properly-regulated solar filter material. However, they are much more widely available.
A suitable material would:
- be made of some type of thin foil;
- be thin enough that a double or triple layer can be used - this is to avoid pinpricks in the material;
- not have any printed coating - this blurs the view - it must give a good clear view;
- filter out 99.997% of UV and visible radiation, and 93% of infrared - this can be tested with a very good spectrometer (e.g. Cary 500), available at some
- not be used if the image of the Sun looks uncomfortably bright;
- not be gazed through for more than about five seconds at a time (just to be perfectly safe).
In South Africa, suitable locally-available materials are:
- the foil inner-box wrapper from Five Roses teabags or Pick'n'Pay Ceylon teabags - use two layers;
- emergency "space blanket" - available from the first-aid shelf of many pharmacies - use three layers.
Anyone locating similar useful material in other countries should please contact us
so we can add yours to the list.
Pinhole Projection under Trees
Look on any sunny day in the shade under a tree for circles of light - these are "pinhole projected" Sun images. You need the right kind of tree -
trees with rounder leaves work better. During an eclipse, the circles will change into images of the eclipsed Sun. This is easier to see if you put
a sheet of white paper on the ground.
This is by far the safest way to look at the eclipse - you're not looking directly at the Sun - and it's very impressive - kids love it.
Other Pinhole Projectors
Write your name in "pinholes" - make pinhole eclipse art.
Make a small hole, with the end of a sharp pencil, in a sheet of paper. Look for the image of the Sun projected through this "pinhole" onto
a second sheet of paper below.
This is simple and safe, but not very satisfactory - the image is small compared to those seen under trees
- because the
"pinhole" is so much closer to the projected image.
However, it is:
- educational - here's a worksheet for teaching how it connects to "light travels in straight lines" (grade 8);
- fun for making "eclipse pinhole art" (and therefore keeping children busy during an eclipse).
You can make an improved pinhole projector using a long box - see instructions from The Exploratorium
Pinhole-projection art from Sirius Travel - specialists in eclipse and adventure travel
MAKE VERY SURE NO-ONE LOOKS THROUGH THE TELESCOPE AT THE SUN.
THIS WOULD CAUSE PERMANENT SEVERE EYE-DAMAGE.
Eyepiece end close to board so people can't look through it.
The wire is to stop people from looking through the eyepiece.
Half a pair of binoculars in a box, to stop people looking through the eyepiece at the Sun.
MAKE VERY SURE NO-ONE LOOKS THROUGH THE TELESCOPE AT THE SUN.
THIS WOULD CAUSE PERMANENT SEVERE EYE-DAMAGE.
A small telescope, or binoculars, will project a bright magnified image onto a piece of white paper.
It is essential that no-one looks through the eyepiece - this would likely blind them - aim the telescope by pointing it towards the Sun, and watching the
shadow of the tube on the projection paper - move the telescope until the shadow is smallest (i.e. the Sun is shining directly along the tube).
The cardboard sheet on the front end of the telescope is to create a dark patch of shade, which makes it easier to see the image.
This kind of setup must be kept under constant supervision, to make sure no-one looks through the eyepiece at the Sun.
Looking through a Telescope fitted with a Solar Filter
IF A SOLAR FILTER BREAKS OR FALLS OF WHILE THE TELESCOPE IS POINTED AT THE SUN,
Some astronomers with backyard telescopes will install sun-filters and look through the telescope directly at the Sun.
Some will take these telescopes to schools and public places, to share the view.
Before you look through one of these telescopes, make sure it is set up safely and professionally:
- the filter must be on the large end of the telescope that faces the Sun - cheap telescopes sometimes come with a "solar filter" for the other (eyepiece) end -
these are fantastically dangerous, as they concentrate heat and can crack without warning;
- the finderscope must be removed - this is a smaller telescope fitted to the body of the larger scope, used to aim the telescope; any experienced astronomer
will remove it (to avoid people looking through it) and cope without it;
- the filter should preferably not be a large sheet of silver mylar, but a smaller filter fitted to a large solid holder - less likely to tempt small children
to poke through it with their fingers;
- the telescope must be under constant and vigilant supervision (see section on children).
THE PERSON LOOKING THROUGH IT
WILL SUFFER SERIOUS AND PERMANENT EYE-DAMAGE..
Children and Eclipses
Viewers can be shared ...
... under controlled conditions!
Children are more susceptible to eye-damage from UV radiation than adults; although UV is more of a long-term-exposure worry than a (brief look) eclipse problem, they should if possible
use proper eclipse-viewers for eclipse-viewing.
Children (and many adults) cannot hear the message "if you do that it will severely injure you
". Do not just warn them not to look at the eclipse
with binoculars - lock the binoculars away
. Do the same with telescopes, and with cameras that involve view-finders.
Children have fantastic recall of the message "if you do that it will severely injure you
" in certain circumstances - if you prevent them from watching the
eclipse, and they find out later that millions of people watched without being harmed, they may justifiably be less likely to pay attention when we warn them about real
dangers such as drug-abuse. Make sure they watch safely, but please let them watch.
Realistically, the view of the Sun through eclipse viewers is tiny, the eclipse progresses slowly, and they can get bored. Organise related activities such
as pinhole-projection art
, and encourage them to photograph the art with their phones.
Photographing the Eclipse
It is perfectly safe to photograph projected images of the Sun.
It is perfectly safe to photograph the actual Sun with a camera that does not involve you looking through a viewfinder - you can safely take photographs
with an ordinary cellphone camera. Put some filter material (e.g. an eclipse viewer) in front of the camera, or you may damage the camera. Don't look at the
Sun while aiming the camera - look at the image on the phone screen.
Expect the results to be disappointing - the Sun is actually very small. You will get a better result with a zoomable camera (including video) - again, don't
look through the viewfinder, and don't look at the Sun while aiming.
It's actually much more fun to photograph pinhole-projected eclipsed Suns - either under a tree or created with pinhole-projection art.
Serious photographers should google "eclipse photography" for professional advice; you will need a filter for your camera.
Facts about Eclipse Eye Damage
The generally-accepted facts about eclipse eye safety are:
* Note: "unaided" in this context means "without using a telescope or binoculars or similar"; "protected" means "protected with eclipse-viewers (or similar)"
- unprotected* gazing at the Sun at any time damages the retina of your eye - whether or not the Sun is in eclipse; the only time it is safe to do this is during the
(rare) couple of minutes of a total eclipse;
- you only have one pair of eyes, and solar radiation damage to them cannot be fixed;
- while you will probably not go permanently completely blind from unaided* unprotected Sun-gazing, the damage is crippling and unfixable;
- even small telescopes (and binoculars) amplify the amount of light reaching your eye (and thus the damage caused) by a factor of around a thousand;
do not look through them at the Sun unless you are a skilled solar astronomer with a proper solar filter (fitted to the objective end);
- the radiation to worry about (because our atmosphere doesn't protect us from it) is UVB (290 to 315nm), UVA (315 to 380nm), visible (380 to 780nm) and
infrared (780 to 1400nm);
- infrared is heat - it literally "cooks" your eye; this won't happen during unaided unprotected Sun-gazing, but it will certainly happen if you look at the Sun
through binoculars or a telescope;
- do not think of looking through a telescope (or binoculars) while wearing eclipse-viewers - the heat will burn a hole in the viewers;
- long-term UV "environmental exposure" is more of a concern than UV from a few seconds of Sun-gazing - it causes cataracts; the cornea and lens in your eye
block much of the UV, so people who have had the lens of their eye removed should be sure to use proper eclipse viewers for Sun-gazing;
- the eyes of children are more susceptible to UV damage - their lenses are less able to block UV - they should use proper eclipse viewers, although
day-to-day environmental exposure is more of a worry - they probably get more UV eye-damage from a day playing on the beach than a few seconds of (protected)
- the huge danger from unaided unprotected Sun-gazing is visible light - this causes photochemical damage to the retina, which causes loss of vision;
- visible light is what you "see" - UV and infrared is invisible to humans; if it's uncomfortable to look, you're damaging your eyes - stop looking;
- photochemical damage from visible light can result from just a few of seconds of unaided unprotected Sun-gazing if the Sun is high and the sky clear;
- photochemical damage is mainly caused by the blue component of visible sunlight - which is why you won't notice any significant damage from unaided
unprotected viewing of the (red) setting Sun;
- the retina has no pain receptors, so you may not notice the damage until much later;
- photochemical retina damage is not 100% understood, the damage will vary from one situation to another - don't take risks; google "solar retinopathy" for
- protective eclipse viewers should be certified as meeting the requirements of either the EN 1836 or the ISO 12312-2 standard on filters for direct observation of the Sun.
The above information was extracted from ISO 12312-2 (safety standards for "Filters for direct observation of the sun"), available (at a price) from
An (older) open-access article by eclipse eye-safety expert Prof B. Ralph Chou, published by NASA, is available here.