total solar eclipse
Photography enthusiasts can take a picture of the historic event using both digital cameras and their smartphonesBeawiharta/Reuters

A total solar eclipse will occur on 21 August, when America will have the rare opportunity to see the sun completely disappear behind the moon. Dubbed the Great American Eclipse, the astronomical event will darken American skies, causing temperatures to rapidly drop, as it passes through 14 US states from Oregon to South Carolina.

Although eclipses aren't considered to be a rare event, an event like the upcoming total solar eclipse has not occurred in the US since 1979. However, there are some dangers involved with witnessing this event, such as looking directly at the sun, which can damage the human eye and even cause blindness. Fortunately, Nasa and other experts have released information about how, when and where people can watch the Great American Eclipse safely.

What is a total solar eclipse?

According to Nasa, a total solar eclipse is caused when the moon and the sun are at the same angular size. Although the sun is 400 times the size of the moon, it is also 400 times far away, which during special circumstance, can make the two heavenly bodies appear as if they are of the same size.

During a total solar eclipse, the shadow of the moon is cloaked in twilight and observes can see this shadow moving towards and away from them, just prior to and after the totality of the eclipse.

"It brings people to tears," Rick Fienberg, a spokesperson for the American Astronomical Society (AAS), told Space.com, commenting on the experience. "It makes people's jaw drop."

When will the total solar eclipse occur and how long will it last?

Although it will take the moon around two hours to completely cover the sun, the duration of the eclipse will depend on the viewer's location. For instance, in Madras, Oregon, the eclipse begins at 9.06am PDT and ends at 11.41am, with totality occurring between 10.19 and 10.21am. However, across the nation, in Columbia, South Carolina, the eclipse will begin at 1.03pm EDT and end at 4.06pm, with totality occurring between 241 and 2.44pm.

Where can you watch the eclipse?

The eclipse will occur on 21 August and will pass through Oregon, Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and South Carolina. Click here to see an animated map of the eclipse's path created by Nasa.

Below are a list of the public parks where you can go to watch the event with friends and family.

Nasa will also live-stream the event. Click here to see how to watch the total solar eclipse live online.

How to photograph the total solar eclipse

Photography enthusiasts can take a picture of the historic event using both digital cameras and their smartphones. According to Nasa, the eclipse can be photographed using a smartphone. However, you will need to put a filter over the lens in your phones as well as cameras when capturing the event. If you're only taking a picture during totality, however, there's no need for a filter.

"Most digital cameras with telephoto lenses of 100 mm or larger will show a disk for the eclipse that will show some detail. As a trial, photograph the full moon at night. Unless you have a telephoto lens for your smartphone, you will only be able to take unmagnified images of the eclipse in your sky," Nasa said. "These photos can be very exciting because the field-of-view is large enough that you can compose the shot with your friends and local scenery in the shot, at the same time a recognizable, eclipsed sun during totality hangs dramatically in the darkened sky."

If you're thinking of using a telephoto lens on your smartphone, Nasa suggests you avoid the "clip on" kind "because they constantly slip and have to be precisely lined up on the camera lens to work." Instead, invest in a lens 12x and above, some of which come with their own smartphone mounting bracket.

"At these magnifications, a tripod is essential because of camera jitter. A decent 12x lens and tripod adapter will cost you about $30.00, but you can also use this system for great 'close up' shots in sport and nature settings too! The telephoto lens will give you enough magnification that you will clearly see some of the details in the bright corona," Nasa said.

US total solar eclipse glasses
Are your solar eclipse glasses safe?Reuters

How to watch safely – what equipment/glasses are needed

The only way to safely look at the sun directly is through solar filters. Nasa advised that viewers stick to using glasses or handheld solar viewers that are not older than three years. However, you can watch the sun directly, without filters only during totality, when the sun is completely hidden from view behind the moon. However, even if a sliver of the sun is noticeable, watching without filters can harm the naked human eye.

"Even when 99% of the Sun's surface (the photosphere) is obscured during the partial phases of a solar eclipse, the remaining crescent Sun is still intense enough to cause a retinal burn," Nasa said. "Note, there are no pain receptors in the retina so your retina can be damaged even before you realize it, and by then it is too late to save your vision!"

Nasa suggests that viewers purchase eclipse glasses and hand-held solar viewers from three companies — Rainbow Symphony, American Paper Optics, and Thousand Oaks Optical — all of who have certified that their products meet the ISO 12312-2 international standard for such products.

"Also, Nasa is partnering with Google and making arrangements to distribute viewing glasses to many institutions and groups along the path of totality."