ECLIPSE VIEWING SAFETY
by Paul D. Maley
Eye safety is RING OF FIRE EXPEDITIONS’ main priority at any observational event involving the Sun. For decades I have provided safety information to people in various countries as well as appearing on TV and giving interviews to the local press prior to and during our solar eclipse expeditions. This has been a critical part of the international outreach of the NASA Johnson Space Center Astronomical Society.
Paul D. Maley and teacher-in-space astronaut Barbara Morgan providing a NASA PAO briefing just 2 weeks prior to the ill fated STS 51L Challenger mission in 1986. Paul briefed several members of the crew on proper ways to observe Halley’s Comet.
Paul D. Maley provides a guest briefing in a hotel prior to an annular solar eclipse
While it is difficult to look/stare at the full sun, the eye has no evolutionary mechanism to pull away from viewing a deep partial phase, where the sunlight is considerably weaker yet still very dangerous!
Proper eclipse observing protocols are important to provide to people in general who are not familiar with astronomy or observation of the Sun at any time. Education is a critical element and it is incumbent on eclipse organizers to bring that knowledge and disseminate it early to avoid problems including eye injury.
Even in modern times there are people in authority who will provide misinformation based on ignorance or who have political agendas. The above photo is an example of an opthamologist in Australia prior to the November 2012 Total Solar Eclipse in Cairns. This person is advising local people not to look at the Sun during totality and during the partial phases of the eclipse even with approved eclipse viewing glasses. There can be no excuse for an irresponsible recommendation like this.
Paul D. Maley outside the TV studios in Lusaka, Zambia prior to providing a presentation to Zambian viewers on how to safely observe the solar eclipse of 2001.
Paul D. Maley being interviewed in Libreville, Gabon in 1986 on how to safely watch the eclipse. The interview was in French and being translated by Jacques and Huguette Guertin.
Your eyes are precious commodities and must not only be protected from the blinding brightness of sunlight in the visual spectrum but also that from the ultraviolet and infrared. Although watching a solar eclipse or planetary transit across the Sun can be an amazing experience, you must exercise great caution to avoid retinal damage as a result or improper observation techniques. Because the eyes have no pain receptors, prolonged staring at the sun could easily result in retinal damage.
Prolonged staring (or even relatively short looking) at the sun is dangerous because the eye concentrates sunlight just like a magnifying glass does with subsequent, strong, heating focused to a point.
In addition, guidance on the type of ‘safe’ solar filter devices may vary internationally due to political, technical and/or social factors related to the country. The following information is based on decades of observational experience by RING OF FIRE EXPEDITIONS.
In the above image three different safe methods are shown. Left: telescope with solar filter mounted in front of the lens; center: observer uses a #14 welder’s glass; right: observer uses binoculars with mylar filters in front of the lenses.
While we concentrate on solar observing during eclipses, there is also similar concern when attempting to see the ‘green flash’ at sunset or sunrise (or other times) since you must ‘see’ the Sun to be sure it is in your field of view for photography. For videography and even photography, the situation is made safer in that if your camera/camcorder is securely pointed and mounted, you can use the screen to keep the camera pointed and focused, thus avoiding the need to visually look through a set of optics.
1. SAFE METHODS for observing the Sun
Observing the Sun can be inherently dangerous but there are ways that eclipse observation can be accomplished safely and without risk.
THE ONLY TIME WHEN YOU CAN SAFELY LOOK DIRECTLY AT THE SUN WITHOUT ANY FILTER PROTECTION IS DURING THE BRIEF PERIOD OF A TOTAL SOLAR ECLIPSE WHEN ALL OF THE SUN’S LIGHT IS BLOCKED. If you are unsure when this will occur, stay close to our tour escort who will signal when it is safe. This ‘free pass’ DOES NOT APPLY for an annular eclipse, partial eclipse, transit of Mercury or Venus across the sun or daily observation of the Sun when none of these phenomena are scheduled.
As a general precaution, never leave any of the following devices unsupervised especially when there are children about. This can be especially true in foreign countries where communication with locals can be problematic.
a. The first and simplest is through the use of pinhole projection, where a hole is poked into one end of a shoebox (or piece of white paper or cardboard) and the sun’s image is projected onto the other side (or onto the ground on another piece of white paper). It may leave you dissatisfied since the solar image is small; if you align the shoe box so that the sun enters the hole on one side, it is projected on the other with some degree of clarity. In the photo below you can see the very small image created by pinhole projection.
b. If you have a telescope or binoculars, either one of these (using great caution to prevent eye injury), you can also project the sun onto a screen or piece of white paper (or screen or white surface) and move it back and forth to adjust the size of the Sun’s image. Any such device should never be left unmonitored and it is advisable to cap both ends when the device is not being used for any period of time. When using binoculars there are two parallel sets of optics involved. It is best to cover one set and use the other for the Sun projection.
The following diagram shows a rather complex setting in which a refracting telescope is used to safely project the image of the Sun.
The Sun should not be projected through this method for any longer than 30 to 60 seconds or so to avoid the ocular [that is, eyepiece(s)] from experiencing severe heating; also you should take care that nobody pick up the telescope or binoculars and look directly at the Sun with them, since they have no sun filter protection.
c. Less complicated perhaps is the use of ‘eclipse glasses’ or ‘eclipse shades’ as they are sometimes called. These are inexpensive cardboard rimmed ‘glasses’ that contain mylar inserts that block the harmful radiation from the Sun when you slip them on. They are NOT sunglasses and the use of sunglasses to look at the Sun should never be attempted as they provide no protection from direct radiation. Before using them or giving them away, be sure to inspect your pair of eclipse glasses to be sure they do not have cuts or pinholes through which light can pass!
In an emergency, you can safely use eclipse glasses on the front of optics. Just be sure that the glasses are securely attached and won’t fall off.
d. A number 14 welder’s glass is also safe to use. It usually produces a greenish image and provides no magnification, but you can follow the progress of a partial eclipse. It is generally not useful for photography.
e. Viewing with or photographing through a telescope or telephoto camera lens is another safe method; Neutral Density #5 (abbreviated as ND5) solar filters can be bought for these devices as optional accessories and such filters are ALWAYS placed in front of the objective lens. A solar filter is never to be attached to the telescope eyepiece!
Before you select such a filter for photography be sure you know how that filter will reveal the Sun. Depending on the filter your sun images may appear blue, green, orange, yellow, or white.
An adjunct to this is viewing the partial or annular eclipse using a digital camera attached to the back of a telescope, where a solar filter has been attached to the front of the telescope. Photography, without a filter, of a very low elevation sun (near or at sunset) can be relatively safe for quick glances (less than ½ s) or by looking at the LCD imaging display/screen on the camera (not through an optical finder). However, if the sun is higher up, a nonfiltered optic can heat up and be damaged and even shatter. If at that moment you are looking through the optics, you can permanently burn your retina resulting in partial or total blindness!
f. mylar or thermal blanket (which is folded in such a way that the overall image of the sun is not very bright). This medium is poor for photography although some specially made mylar filters can be used for this purpose. Keep the foil is flat as possible. If the image of the Sun appears too bright, do not use it.
g. projection also includes looking at the ground for crescent images projected through certain types of leaf patterns on trees (not during the total phase of a total solar eclipse)
h. projection may also include interlacing fingers and looking at the ground as small out of focus crescent suns are projected (not during the total phase of a total solar eclipse)
i. Baader solar film. This is an ideal product developed for the solar eclipse of 1999 in Europe that has received rave reviews.
j. Sun funnel. This is a projection device that can be constructed and attached to a telescope eyepiece. See: http://transitofvenus.nl/wp/observing/build-a-sun-funnel/
For those interested in more serious photos or videos, this can be accomplished with a digital camera/telephoto combination of 600mm fl or longer or a digital camera back attached to a high quality apochromatic refractor (for example) or off-the-shelf camcorders. Again, you must have proper ND5 filtration in front of any camera lens during the entire portion of the annular eclipse and during the partial phases of a total solar eclipse. Remember that it is only safe to view the totally eclipsed sun without a filter during the short time period identified by our tour escort. Prior to the expedition we provide a photo guide to help you determine the proper exposures.
This can be a rather bulky device to transport but is excellent for showing people the progress of a sun eclipse.
By far the safest method (and least direct) is to look at the eclipse on television or by live streaming on the internet. This technique certainly protects viewers eyes but eliminates all enjoyment of the grand spectacle that can be a solar eclipse.
2. UNSAFE METHODS to view the sun
Paul D. Maley providing a briefing on unsafe methods which are just as critical as knowing how to safely watch the eclipse.
The following methods you must avoid since they pose a significant hazard to your eyes or to those of someone who might wander up to your instrument. Some of these methods may appear safe at first use but they are not!
a. direct viewing of the sun with binoculars or telescope or any devices with lenses that do not have a neutral density 5 filter IN FRONT of the optics. Remember that if your telescope has a finder scope, it must either have a filter or be covered when not in supervised use.
b. direct viewing of the sun through a CD or DVD
c. looking at the reflected image of the sun in a pail of water, mirror or other reflecting medium
d. direct viewing of the sun with any type of sunglasses or polarizing glasses
e. attaching a screw-in solar filter to the end of a telescope eyepiece, then looking at the sun with the telescope. These are sometimes called solar eyepieces or sun filters and may be in the box when you buy certain inexpensive telescopes.
f. viewing with special “eclipse glasses” that have cuts or pinholes through which sunlight can pass
g. use of x-ray film (exposed or otherwise)
h. prolonged viewing of the sun without proper filters through cloud. If thick clouds are present, only quick glances (less than ½ s) are safe.
i. direct viewing of the sun through cloth mesh (as was reported in Ghana in 2006)
j. smoked glass
k. use of color or black and white film (exposed or otherwise). The example below shows what should NOT be done. At our international venues we attempt to provide safe observing instructions to local people whenever possible.
l. Other things to avoid include placing objects in front of your eyes such as a giant pizza. This ad appeared in 1997.