On Sunday, millions of people around the world will be treated to an amazing sight: an annular solar eclipse in which the moon will cover as much as 94 percent of the sun, leaving a glowing ring of fire.
In the US, the eclipse will begin around 5:30 pm PDT and last around two hours. The greatest coverage will be at around 6:30 pm PDT. The last such eclipse to be seen in the US took place in 1994, and the next will be in 2023.
Because some of the sun is always exposed during the eclipse, the amount of daylight fall dramatically - but looking at the ground beneath leafy trees will reveal crescent-shaped sunbeams and rings of light.
The 'path of annularity' where the ring of fire can be seen is only about 200 miles wide, covers a swathe of the southern US - southwest Oregon, Northern California, central Nevada, southern Utah, northern Arizona, New Mexico and the Texas Panhandle. The effect should last for around four and a half minutes.
Outside this band, other areas will see a partial eclipse.
"The ring of sunlight during annularity is blindingly bright," cautions NASA's leading eclipse expert Fred Espenak of the Goddard Space Flight Center.
"Even though most of the sun's disk will be covered, you still need to use a solar filter or some type of projection technique. A #14 welder's glass is a good choice. There are also many commercially-available solar filters."
If you buy one, you'll get another chance to use it two weeks later when Venus makes a transit of the sun.