Baily’s Beads – Brilliant String of Sun Diamonds

The year 1836. The place, Inch Bonney in southern Scotland. This was the first good opportunity to observe a total or annular solar eclipse in his lifetime and he was determined not to miss it. Our protagonist, Francis Baily.

Francis Baily did well, amassing a small fortune in the financial arena and retiring at age 51. In those days, men of means and time frequently found a serious hobby, like astronomy. Baily went all in. His interest was mainly in star catalog development – that’s serious! He went on to become a founding member of England’s Royal Astronomical Society, getting elected president 4 times. Not too shabby.

After years of cataloging stars – I just can’t find that interesting but that’s me, Baily changed his focus to solar eclipses. OK, that was perhaps a challenge he had not anticipated, because there weren’t eclipses happening, so he waited patiently. When finally the time came, he was prepared with his 2.6-inch f/15 (think department store telescope, really) refractor and some accessories. Off he went to Scotland.

From other astronomer’s descriptions, an annular or total solar eclipse has two very special and surprising events. The events happen as the dark, curved limb of the Moon gets nestled into the Sun’s limb, with just the tiniest sliver of sunlight showing. Then something magical happens. Baily couldn’t wait!

The partial phase of this solar eclipse was as expected. When the Moon’s trailing limb had just made it past the bright Sun’s limb, now only minutes until annularity, it happened. At the limb sunlight shown like a necklace of brilliant diamonds sparkling along the Moon’s dark edge. The brilliance of these diamonds was variable. Between the numerous diamonds were black spaces of different lengths and unevenly spaced. As Baily continued his observation, the black spaces between the brilliant light elongated into parallel lines, seeming to communicate with the Sun’s disk.

Then boom, gone. The sideshow finished and now the main event was on full display. Annularity, with its thin “ring of fire” surrounding a seeming black hole. The Moon’s limb slowly crept toward the Sun’s other side and as they were just about merge it happened again – the string of diamonds. Baily was astounded and pleased to have witnessed this event. He went on to document and report on his observations.

Interestingly, Francis Baily wasn’t the first to observe and document a string of diamonds forming when the limb of the Moon and Sun are just about to merge. In 1715 Sir Edmond Halley wrote about seeing them in his observations log. See what happens when you don’t publish or otherwise disseminate information like this? You don’t get your name associated with it.

Both Halley and Baily correctly described this phenomenon as the Sun’s photosphere shining between lunar mountains and along valleys. Of course, Baily’s report got published and this phenomenon is called Baily’s Beads, not Halley’s Beads.

What’s in the Sky?

I hope you enjoy a safe and beautiful annular eclipse.