A partial solar eclipse will be visible across the UK just before sunset as the moon appears to take a "bite" out of the sun.
The phenomenon will last roughly 40 minutes, with the mid-point occurring at different times around the country.
For observers in Edinburgh, the peak of the eclipse will be at 7.58pm and for those in Cardiff at 8.05pm.
The movement of the moon between the Earth and sun will produce a much more dramatic event in the US, where a total eclipse will turn day to night for two minutes.
Millions of Americans are gathering along a stretch from Oregon to South Carolina to watch the spectacle - the first total solar eclipse to sweep coast-to-coast across the US in 99 years.
Southern-most Illinois will see the most darkness at two minutes and 44 seconds.
It is expected to be the most observed and most photographed eclipse in history.
Up to five solar eclipses occur each year, but each one is visible only within a limited band across the Earth's surface where the moon's shadow happens to fall.
The Royal Astronomical Society warned anyone hoping to catch the phenomenon not to look directly at the sun.