ONLINE EXTRA: Don't Be Afraid of the Dark

ANGELA SPECK, director of astronomy, University of Missouri, Columbia, Missouri

On August 21 there will be a total solar eclipse visible from a vast swath of the USA. Approximately 12 million people live within the path of totality (from which the TOTAL eclipse can be seen); the entire nation gets a significant partial eclipse that day. The last time the US had a total solar eclipse was in 1991, but that was only visible from Hawaii. The last time a total solar eclipse was visible from the continental US was 1979, and then only in the northwestern-most states. This will be the first total solar eclipse to cross the entire continent since 1918 and the first to be visible from ONLY the US since before the US became a country.

The upcoming total solar eclipse provides great opportunities for engaging kids in all aspects for science, from solar physics to atmospheric science to how life responds to darkness. However, there is still much misinformation floating around about what we can see and otherwise experience, when it is safe to look and even whether it is safe to be outdoors. Here, I explore the myths about safety and danger during a total eclipse of the Sun.

Ancient cultures have many stories about the causes and dangers of eclipses. There are also modern myths; some even make it into textbooks. For instance, there is a myth about it being dangerous to view the Sun's corona (outer atmosphere), which is only visible during totality (the total phase of the eclipse, when the main bright disk of the Sun is completely blocked.). Adults from Washington State, now in their forties and fifties, even tell stories of how they were denied the opportunity to watch the total solar eclipse in 1979. Some kids hid under desks in classrooms with blackout curtains drawn, as if any sunlight on them would be damaging. This was perhaps due to the myth that the Moon can somehow focus the light of the Sun during an eclipse, making the light even more intense than usual. Fear kept people indoors and they watched the event on TV.

In truth, a solar eclipse day is not more dangerous than a normal day. The focusing of sunlight is said to be caused by the Moon's atmosphere; however, the Moon does not have an atmosphere; the Moon simply blocks the sunlight. No focusing occurs.

During a solar eclipse, the Moon is lined up in front of the Sun, blocking our view of the Sun and stopping its light from reaching a small area of the Earth's surface. The moon is no closer to Earth and no closer to the Sun than on any other day (within the normal range of variation). The Moon and the Sun are in the same direction, but just as one can block out a distant bonfire using one's thumb, there is no dangerous relationship between the Moon and the Sun at the moment of eclipse.

Temporarily blocking sunlight from reaching a fraction of the Earth's surface does have some interesting effects: it goes dark, we see stars during the day, it gets colder, air currents are generated, animals and plants react to the reduction in light, and solar power plants have reduced power generation. However, the action of the Moon blocking sunlight is not intrinsically dangerous.

Unfortunately, there are some real dangers associated with viewing an eclipse. On any normal day we know we should not stare at the Sun; we know that the Sun's light is strong enough to do damage. This is true every day. Most days, we have no incentive to stare at the Sun, but during eclipses, we actually want to look. It is not that staring at the Sun is more dangerous during an eclipse – it is just as dangerous as any other day – but, since we want to look at the Sun in an eclipse, we need to have safe methods for watching.

The only time it is completely safe to stare at Sun is during totality, to view the Sun's corona. At this time, the light emitted is only about as bright as a full moon and will not damage your eyes. Myths about the safety of viewing the corona may have originated from the fact that we cannot see the corona outside of a solar eclipse. This led to the belief that the corona is created by the eclipse, and something to be feared. However, the corona is always present, and the reason we can't usually see it is because it is very faint compared to the main bright disk of the Sun and so remains hidden except during a total solar eclipse. Although the corona is very hot (~2 million Fahrenheit!) and emits X-rays and ultraviolet light, the corona is not dangerous to life on Earth because our atmosphere protects us.

On the day of the Great American Eclipse, keep in mind that although the Sun's rays are no more intense than on any other day, the only time to safely watch the event without any special equipment is during totality.

During the partial eclipse phase, as the Moon transits across the face of the Sun and part of the main bright disk is still visible, the Sun is too bright to view without protection, just like on any other day.

So go and watch the eclipse. View it safely. And don't be afraid of the dark.