Edward Pigott and the discovery of R Corona Borealis in 1795

This year is the 200th anniversary of the death of Edward Pigott one of the ‘Fathers of Variable Star Astronomy’ this was a title I gave him and the deaf astronomer John Goodricke who between 1781-1786 would make incredible advances in the discovery and study of the branch of astronomy we know of today as variable stars.

 Pigott was born in Whitton, west London in 1753 and died on June 27th, 1825. His life would make an incredible soap opera story, but much more of that later.

Edward Pigott

Here is another of a series of highlights from his incredible career.

Following the death of his friend and colleague John Goodricke in York in 1786, Edward Pigott finally decided to leave York and move to the city of Bath in1793. He would soon start looking for variable stars.

One of the stars he was following was in the constellation of Corona Borealis the Northern Crown. This star which we recognise today as the star R Corona Borealis (RcB) is the prototype star of a group of only about 150 stars of this type. 

Pigott started observing the star from July 1783 while he was in York, by the spring of 1795 he was able to confirm that it varies in brightness. He would continue to monitor the star through 1796. When at its maximum brightness it was of the 6^th magnitude just about visible to the naked eye under the very best of condition but when at its faintest it was invisible in Pigott’s telescope. Pigott identifies this period of light variation taking around ten and a half months.

Pigott stated that although it was not in the catalogue of John Flamsteed of 1725 it  was listed in the star atlas of Johann Bayer from 1603 as being of the 6^th magnitude. This would suggest that it was at its brightest when Bayer produced his star atlas.

Pigott noted that when R CrB was either fading or brightening it did so at an uneven rate. This was different to the stars Algol and eta Aquila that he had observed, the light curve on a graph of Algol and eta Aquila were very smooth while that of R CrB was more jagged. He was very curious to the fact that it disappeared for a period before re appearing. He believed that further observations would be needed to confirm the period of ten and a half months for this star was correct or not.

Today astronomers know that the star will remain at it brightest for many months or even years before fading in brightness. It will then return over a long of time period to its brightest. Pigott was wrong in his calculation that R CrB varied over a period of about ten and a half months. This was simply since he was not able to observe the star for a long enough period to see how irregular the light variations were.

As I mentioned R CrB is the prototype star for this small group of stars. The cooling is caused by a cloud of soot which forms around the star from the condensation of carbon rich dust in the star. As the dust cloud forms the star is masked by this cloud of dust, the brightness of the star is affected, and we see the star fade in brightness. Then when the cloud of soot clears R CrB returns to normal brightness.

R CrB is an old star and is only one of two stars in this class that can be seen with the naked eye the other is RY Sagittarius. All the other stars in this class need telescopes to follow their cycles.

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