An eclipse results from the precise alignment of the Sun, Earth, and Moon in space. A solar eclipse occurs when the Moon passes between the Sun and Earth, casting its shadow upon our planet and obscuring the Sun’s bright disk. A lunar eclipse happens when the Earth passes between the Sun and Moon, enveloping the Moon in Earth’s shadow. Witnessing these astronomical phenomena requires preparation to ensure the experience is both memorable and safe.
Essential Eye Safety
The most important consideration when viewing a solar eclipse is the danger posed by the Sun’s radiation. Looking directly at the uneclipsed or partially eclipsed Sun, even for a few seconds, can result in a permanent eye injury known as solar retinopathy. This damage is caused by the intense visible light, along with high-energy infrared and ultraviolet (UV) radiation, which focuses onto the retina and can cause a thermal burn to the photoreceptor cells. The retina lacks pain receptors, meaning this serious injury can occur without any immediate warning of discomfort.
Protection is mandatory during all partial phases of a solar eclipse, which can last for over an hour before and after totality. The danger persists because even a tiny sliver of the Sun’s visible surface emits enough radiation to cause retinal damage. Standard sunglasses, regardless of their darkness or price, are not adequate to block the harmful rays and must never be used for solar viewing. Household items like smoked glass, exposed photographic film, polarizing filters, or compact discs are also ineffective and should be avoided, as they do not meet safety standards for filtering solar radiation.
Never attempt to view the Sun through an unfiltered camera, telescope, or pair of binoculars, even while wearing eclipse glasses. The concentrated solar rays passing through the optics will instantly destroy the protective filter and cause eye injury. Children are particularly susceptible to this damage because their pupils transmit more light to the retina than adult eyes. Therefore, constant supervision and strict adherence to certified safety methods are imperative throughout the partial eclipse.
Approved Methods for Direct Viewing
Safe, direct observation of the solar disk requires specialized equipment manufactured to meet an international safety standard. This equipment includes certified eclipse glasses and handheld solar viewers that comply with the ISO 12312-2 standard. This designation confirms that the filter material reduces the transmission of visible sunlight to safe levels and effectively blocks harmful UV and infrared radiation. These specialized filters are thousands of times darker than regular sunglasses.
Before using any certified viewer, inspect the filter material for any signs of damage, such as scratches, tears, pinholes, or separation from the frame. Any damaged viewer must be discarded, as even a small imperfection can compromise eye safety. The proper technique for using eclipse glasses involves putting them on before looking up at the Sun. Conversely, viewers should look away from the Sun before removing the glasses to prevent accidental exposure to direct sunlight.
For those using optical devices such as telescopes, binoculars, or cameras, a certified solar filter must be securely fastened over the front aperture of the equipment. This placement is necessary to block the Sun’s energy before it enters and concentrates within the optical system. Using certified filters in this manner allows for a magnified, safe view of the solar eclipse’s progression.
Indirect Viewing Techniques
Indirect viewing uses projection to display an image of the Sun. This technique allows viewers to observe the event without ever looking directly at the Sun or needing specialized eye protection. A simple pinhole projector can be constructed using two pieces of sturdy white paper or cardboard.
A small, clean hole is made in one piece of material, often using a pin or thumbtack, to act as the aperture. Holding the paper with the pinhole up to the Sun, with your back to the light source, allows the sunlight to pass through the opening. The second piece of paper is held a short distance away to serve as a screen, where a small, inverted image of the Sun is projected. The longer the distance between the pinhole and the screen, the larger the projected image of the partially eclipsed Sun will appear.
Natural objects can also function as pinhole projectors. The small gaps between the leaves of a tree, for instance, create apertures. During the eclipse, the light passing through these spaces projects numerous crescent-shaped images of the partially covered Sun onto the ground or a nearby wall. Items with small perforations, like a colander or a straw hat, can similarly be used to create a pattern of projected solar crescents.
Viewing Lunar Eclipses
Unlike solar eclipses, a lunar eclipse is safe to view with the unaided eye and requires no eye protection. This is because the celestial event involves viewing the Moon as it passes into the Earth’s shadow, meaning the light reaching the viewer is merely reflected sunlight off the Moon’s surface. The Moon’s brightness during an eclipse is comparable to a normal full moon, posing no risk of eye damage.
Viewers can use binoculars or telescopes to enhance their view of the lunar surface details without the need for solar filters. During a total lunar eclipse, the Moon frequently takes on a reddish or coppery hue, often referred to as a “blood moon.” This coloration occurs because some sunlight is refracted by Earth’s atmosphere, scattering blue light away and bending the longer-wavelength red light onto the Moon’s surface. The best viewing conditions occur under clear, dark skies, away from light pollution, allowing the subtle color shifts and the contrast of the Earth’s shadow to be appreciated.