Solar eclipse 2017: Nasa issues safety guide to people waiting for the sun to disappear

The spectacle over the US is set to be the most viewed eclipse ever. And potentially the most dangerous

Picture taken on February 26, 2017 showing the moon moving to cover the sun for an annular solar eclipse (ALEJANDRO PAGNI/AFP/Getty Images)

A total solar eclipse is set to sweep over America. But making sure that everyone there can enjoy it is important work.

It is one of the most stunning sights that can ever be seen in the sky, and the opportunity to do so only emerges rarely. The whole of North America will get that chance on 21 August, when a total solar eclipse will make its way across the continent, turning day into night.

But it is also highly dangerous, and viewing it wrong can damage people's eyes and the equipment used to do so. That's why Nasa has published a guide to watching the eclipse safely and happily.

The central problem with the eclipse is that the star of the show is the sun. Even though it will be sliding behind the moon and out of proper view, all the normal caution must apply, since looking straight at it can cause such damage.

As such, Nasa says that anyone looking to observe the eclipse must not do so directly. Instead, you can either use eclipse glasses, which work like very intense sunglasses, or an indirect method.

Those filters are the only safe way to look right at the sun as the eclipse is moving into place. Nasa warns that anyone doing so must be careful to ensure their eclipse glasses – which should be available for purchase in most places – are safe.

That means that they shouldn't have scratched, damaged or wrinkled lenses, or be more than three years old. They should include the manufacturer's name and address – which can be checked online – and guarantee that they confirm with the ISO standard.

To use them, stand still and put on your sunglasses while not looking up at the sun, and then look towards it. Make sure to do the same when you remove them.

The only time it's safe to look right at the eclipse is when it reaches totality, and the sun passes behind the moon and turns day into night. That will last for about two minutes and 40 seconds, after which you'll need to put them back on.

If you're not using eclipse glasses, then there are other indirect methods you can use. Those include pinhole cameras – instructions for making one can be found here – or using a projecting telescope to show the image. Of course, all of those methods can be used in conjunction with glasses, letting you see the eclipse in a number of different ways.

Perhaps the best method of all is to search out your local observatory or astronomy group, and meet up with them. Organisations across the continent will be holding events to allow people to look safely at the eclipse, as well as running other activities too.