Though only people along the narrow path of totality will see the total eclipse, millions more will see some degree of a partial solar eclipse in Asia and the Pacific, including Hawaii, Guam and parts of Alaska.
A partial eclipse will also be visible along the path of totality for over an hour before and after the total eclipse.
As the Moon passes precisely between the Sun and Earth — a relatively rare occurrence that happens only about once a year because of the fact that the Moon and the Sun do not orbit in the exact same plane — it will block the Sun’s bright face, showing the tenuous and comparatively faint solar atmosphere, the corona.
“You notice something off about the sunlight as you reach totality,” said Sarah Jaeggli, a space scientist at NASA’s Goddard Space Flight Centre in US.
“Your surroundings take on a twilight cast, even though it’s daytime and the sky is still blue,” Jaeggli said.
Totality will last for anywhere from one and a half to just over four minutes at each location, though more than three hours will pass between the time the westernmost location sees the eclipse begin and when the easternmost location sees the eclipse end, according to NASA.
People along the path of totality — which is over 14,162 kilometres long, but only 156 kilometres wide at the widest point — will have the opportunity to see the solar corona only while the Sun’s face is totally covered by the Moon.
“The Moon blocks the light of the Sun’s surface very, very precisely,” said Jaeggli.
“You can see all the way down to the roots of the corona, where the atmosphere meets the Sun’s surface,” she said.
Total solar eclipses like this are possible because of very precise planetary geometry. The Sun is 400 times wider than the Moon, but it is also a little more than 400 times farther from Earth than the Moon during total solar eclipses, so to our eyes they appear the same size in the sky.
This means the Moon can block the entirety of the Sun’s face while obscuring only a tiny portion of the inner corona.