Bright flashes of light from around the rim of the moon are a moving spectacle during Totality
The Moon is not flat. It’s covered in mountains, valleys, and craters, and consequently, sunlight travels through them irregularly.
And it gives us one of the best sights of all during an eclipse, Baily’s Beads.
As the eclipse edges towards Second Contact – the moment when Totality begins – the sun’s light is almost completely blocked by the Moon. All that’s left are small, receding points of light that around the irregular shape of the Moon’s disk. These are known as Baily’s Beads.
Look at any 99% full Moon (preferably with binoculars or a telescope) any month of the year and you can see long shadows being thrown across the lunar surface. The poles are also dotted with mountains and valleys, which are what produce the beads of light.
Finding Baily’s Beads during a Total Solar Eclipse
As these beads shrink, a beautiful Diamond Ring effect is created; a circle around the Moon with an apparent ‘jewel’ of sunlight. Then they disappear as Totality begins. Just before Totality ends the beads return, this time growing to crate another Diamond Ring that culminates in a huge flash of sunlight – and the eclipse is over.
No one ‘discovered’ these beads of sunlight, but the first astronomer to describe them was English astronomer Sir Francis Baily, who witnessed them during an annular eclipse on May 15, 1836. However, there is evidence that another English astronomer, Edmund Halley – the first to calculate the orbit of a comet (Halley’s Comet) – saw them in the UK during an eclipse on April 22, 1715.
Photo credit: Nick Glover