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The sun is the brightest object in the skies of Earth. Like other stars, it consists of hot gases- approximately 75% hydrogen, 25% helium, and less than 1% of oxygen and other elements. The source of the sun's power is nuclear fusion. Hydrogen, with one proton and one electron, fuses into helium with two protons and two electrons. During this fusion process, they drop off a tiny amount of mass, which is metamorphosed into energy, releasing heat at around 15,000,000 degrees Celsius. Even though the sun drops off half a million tons of mass every second, it will carry on to glow for approximately five billion years.
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When Can You View the Sun Without Risk?
No risk of damage to the eye is involved when you view while the sun is very low in the sky. This is during the time when the color of the sun is yellow or orange, suggesting that the risky blue light has been dispelled out of the straight path of sunlight and the sun is observable for many moments without peril. This situation calls for some judgment and caution, but it is worth going through since there is a very big and fast alteration in the intensity of the Sun near sunset.
For instance, the least likely atmospheric disintegration constant at sea level in blue light is around 1/4 stellar scale per air mass. When the Sun is 5° over the galactic view, the atmospheric state is about 10, so the blue light is cut down by no less than 2.5 magnitudes, or a divisor of 10. This would normally not allow a threshold burn to build up in 100 seconds; if we presume the injury depends only on full exposure, then 1000 seconds is needed, presuming brightness remains fixed.
However, at short parallels, the Sun adjusts in 20 minutes or 1200 seconds after attaining an altitude of 5° and in this time, its luminance quickly decreases. This indicates that, at low lines of latitude, gazing at the Sun for the entire 20 minutes ahead of sunset may be slightly sufficient to create a threshold photochemical retinal lesion in a medium eye. Since sensitivity varies we cannot say that all eyes would inevitably be free of harm at this point.
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Risks Involved while Gazing at the Sun
The diameter of the human eye is less than 3 cm (1.2 inches); moreover the pupil is under 1 cm (roughly 0.3 inches). Thus you can imagine the relatively scarce amount of energy our eye can collect. Conversely, the Sun gives out a galactic quantity of energy.
Actually the Sun gives out approximately 64 million watts per square meter (W/m2) of energy, but as that discharge is in all directions, the quantity that arrives at the Earth is merely under 1400 W/m2, and this is known as the solar constant. Thus if you were looking straight at the Sun, the eye would gather in about 4 milliwatts. This solar energy is diffused all over the solar spectrum resulting in some wavelengths being more hazardous than others.
Consequently the Infrared wavelengths somewhat heat the retina, causing optic artifacts or eye impairment which may cause temporary to permanent blindness, depending on the length of time you were to expend gazing straight at the Sun. These impairments are induced by erythematic-like injury to the retina. The harm caused by the infrared waves can be further aggravated if a child's eyes or a person with new lens grafts, or if the Sun tilts near the celestial point.
Even though utraviolet light is quite risk-free to the retina, extended contact to UV light tends to somewhat yellow the eye lenses, making them denser with the passage of time, which ultimately heads to cataracts.
All these troubles are significantly enlarged when you use light gathering tools like binoculars and telescopes that focus the luminosity from the Sun. Many of you know how a fire is started with a magnifying glass, but the fact that a telescope can direct much more light than an magnifying glass is not known to all. Sunlight amplified by a 10-inch reflecting telescope can burn down through six levels of 1 millimeter solid cardboard within seconds. Just imagine how this would affect your eyes!
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How to view the sun safely
The best way to watch the Sun is by utilizing some sort of sun filter. There are several kinds on the market, ranging from cheaper ones to more costly ones.
In the least expensive class you have canvases of high concentration polymers. At first glance these sheets might be mistaken to be aluminum foil, but they are very diverse, since they obstruct not only seeable light, but also infrared light. The setback with these polymers is that they mortify rather quickly and are very delicate, so be careful not to utilize them for a lengthy time. A similar result can be attained with some kinds of soldering glasses. Nevertheless, to gaze at the Sun safely, welding glasses must be no less than #14, and also remember not to use them with light gathering tools like telescopes.
Even though the inexpensive version of concentrated polymers can be utilized in telescopes, typically telescope filters are like mirrors. They also mirror nearly all the brightness that glows in them, but always only a very minute fraction of light enters through a mirror. Thus when you gaze at the Sun, it is precisely that small amount that is not dangerous to watch. I would like to caution you here please not use your bathroom mirror to gaze at the sun since it is not expressly contrived for solar watching.
Yet another type of filter, which can be utilized to watch specific wavelengths of sunlight, as the H-alpha filter. The reason these work is that tthey obstruct sunlight by passing only a narrow frequency range.
As a final point say that you do not desire to expend any money, then you can use a safe but indirect watching technique with the help of a pinhole optical instrument known as a projector. Similar in operation and theory to a pinhole camera, this projector has a tiny opening that helps in forming a picture of the Sun on a surface located almost a meter away at the rear of the opening.
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Conclusion and references
I would like to conclude this article by a word of caution; do now use any kinds of tricks which some urban legends talk about to observe the sun. Do not specifically use the following:
- Uncovered pictorial film
- Fumed glass
- Medical X-ray pictures
- Floppy magnetic disks
Even if the above mentioned tools appear to obstruct an adequate amount of the Sun's luminosity, they either do not guard your eyes from UV or infrared light, resulting in some kind of damage to your eyes.
Science Daily - Spotting the Sun Spots
Beginners Guide - how-can-i-observe-the-sun-safely
Sherwood Harrington - The Nearest Stars: A Guided Tour
Andrew T. Young - Galileo, solar observing and eye safety