This Date in Science: Baily's Beads Discovered

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May 15, 1836. On this date, Francis Baily, an English astronomer, saw beads of sunlight shining along the edge of the moon’s silhouette during an eclipse of the sun.

It was an annular eclipse – nowadays often called a ring of fire eclipse – meaning that the moon was too far away in its monthly orbit around Earth to appear large enough in our sky to cover the sun completely. At mid-eclipse, Baily saw beads of light shining around the darkened moon. They resembled beads on a string. Later, it was realized that these beads of light appeared due to the presence of mountains, crater walls and other topographic features extending above the limb, or edge, of the moon as seen from Earth.

This phenomenon, which can be seen during both annular and total eclipses, is now known as Baily’s Beads.