Sun

::{{otheruses}} For the astrological significance of the Sun, see Solar system in astrology.

Sun and eye damage

Sunlight is very bright, and looking directly at the Sun is painful to the eyes. Looking directly at the Sun when it is high in the sky causes temporary bleaching of the photosensitive pigments in the retina, which makes phosphene visual artifacts and may cause temporary partial blindness. Direct viewing of the Sun with the naked eye delivers about 4 milliwatts of sunlight to the retina that is in the solar image, heating it up and potentially (though not normally) damaging it. Brief viewing of the direct Sun with the naked eye is unpleasant but generally safe. Long-term exposure of the eyes to direct sunlight contributes to the normal UV-induced yellowing of the lens and cornea over periods of decades, and could play a part in the formation of cataracts.

Related Topics:
Bleaching - Retina - Phosphene - Naked eye - UV - Cornea - Cataracts

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Viewing the Sun through light-concentrating optics such as binoculars is hazardous without an attenuating (ND) filter to dim the sunlight. Suitable filters are available at welding supply shops and camera stores. Viewing the Sun through unfiltered 7x50 mm binoculars can deliver as much as 2.5 watts of sunlight into each eye, over 300 times more power than naked eye viewing. Even brief glances at the midday Sun through binoculars can cause permanent blindness.

Related Topics:
Optics - Attenuating (ND) filter - Welding

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

During partial eclipses of the Sun, another hazardous condition exists because of the way that the eye responds to bright light. The pupil is controlled by the total amount of light in the visual field, not by the brightest object in the field. During partial eclipses, most sunlight is blocked by the Moon passing directly in front of the Sun, but the uncovered parts of the photosphere have the same surface brightness as during a normal day. In the dim overall light, the pupil tends to dilate from about 2 mm to perhaps 6 mm diameter, increasing the eye's collecting area by a factor of nearly 10. Each retinal cell that is exposed to the partially-eclipsed solar image thus receives about ten times as much light as it would looking at the normal, non-eclipsed Sun. Viewing the partially eclipsed Sun with the naked eye can cause permanent localized damage to the retina, resulting in small, permanent blind spots for the viewer. This is an especially insidious hazard for inexperienced observers and for children, because there is no immediate perception of pain and it is tempting to stare at the spectacle of the eclipsing Sun, compounding any damage.

Related Topics:
Partial eclipses - Pupil - Surface brightness

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

During sunrise and sunset, sunlight is attenuated by a particularly long passage through Earth's atmosphere, and the direct Sun is sometimes faint enough to be viewed directly without discomfort. Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation. However, it is still very dangerous to view the Sun with binoculars at such times, as ultraviolet light is much less affected by haze and dust, and so its capacity to damage the retina is not reduced.

Related Topics:
Sunrise - Sunset - Atmosphere - Ultraviolet

~ ~ ~ ~ ~ ~ ~ ~ ~ ~