Skywatchers in the United States are preparing for a spectacular eclipse that is without precedent in their country’s 241-year history.
A total solar eclipse will sweep across the nation on Monday, from Oregon on the west coast to South Carolina on the eastern seaboard.
It is the first such eclipse to make landfall exclusively in the US since the country’s independence in 1776.
Total solar eclipses see the Moon slip between the Earth and the Sun.
The Moon’s diameter appears to be the same size as that of our star and so blocks out its light.
A giant shadow cast by this occultation then races across the surface of the Earth, plunging locations into darkness for a couple of minutes or more.
Those not directly under the Moon’s shadow get to experience a partial eclipse which on this occasion will encompass all of North America and northern parts of South America.
There are even parts of western Europe, including the UK and Ireland, that will snatch a sight of the Moon’s disc taking a bite out of the Sun just as it sets.
Wherever people watch the drama unfold, they are urged to take care. Looking directly at the Sun with the naked eye can be dangerous.
The 21 August eclipse is the first since 1918 where the path of totality crosses both the Pacific and Atlantic coasts of the US.
Many commentators believe it will prove to be the most observed, most photographed, and best documented such event in human history.
It will certainly challenge the numbers that saw the 2009 eclipse that swept across India and China.
The US, of course, has excellent transport connections, and this will help many people get into a good position.
As it is, more than 12 million people live on the path of deepest shadow (“totality”). Nearly four times that many live within a two-hour’s drive, and over 200 million live within a day’s drive.