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.
I have already indicated how good an observer Edward Pigott
was, here is an example of his patient watching of the skies. On September 10th,
1784, he would discover a new variable star, on the same night John Goodricke
would also discover new variable star. Two new variable stars in one night,
this certainly was a night to remember in York. Up until now astronomers only
knew of 5 other variable stars.
I would like to concentrate on Pigott’s discovery. Since
July 17th, 1783, Pigott had been observing the star we now call eta
Aquila. Interestingly it was not always in the constellation of Aquila the
Eagle.
The constellation of Antinous had been known since ancient
times when the Greeks saw it as Ganymede a youth bought to his lover Zeus by
the eagle Aquila. The Romans then changed it to represent a friend of the Roman
emperor Hadrian.
The constellation of Antinous was represented by stars immediately below Altair the brightest star in the constellation of Aquila the Eagle. Eta marked the head the rest of the outline are represented by the star’s sigma, theta, iota, kappa, lambda, nu and delta.
The star that Pigott was observing was eta Antinous, now it
is eta Aquila as the stars that made up Antinous were by the later part of the
19th century incorporated in the constellation of Aquila.
The idea of using Greek letters to identify stars in a
constellation was introduced by the German astronomer Johann Bayer in 1603. In
theory alpha is brightest then beta all the way down to omega which is the 24th
and last letter of the Greek alphabet. Sometimes this works and sometimes it
does not. If you look at the brightness of star in a constellation alpha is not
always the brightest star.
Pigott saw that it varied in a regular fashion rather like
Algol in Perseus. With eta around every 7 days the stars faded and then
returned to its normal brightness. Also,
like Algol the changes in brightness could be observed with the naked eye, no
telescope was needed. He continued to observe the star until December 1784.
In concluding that eta Antinous was like Algol, Pigott was
wrong. However, we can hardly blame him for concluding what he did. They simply
did not know what was going on inside stars. Both Pigott and Goodrick were
taking the view that any star that changed in brightness in a regular way must
have an unseen companion going around it.
Today we know that eta Aquila to give its modern designation
is a variable star that varies in a very regular way. This is due not to some
unseen companion orbiting it but to an internal mechanism. Astronomers have
classified eta Aquila as a cepheid variable, these are stars that are used by
astronomers to measure distances in space. The first cepheid variable delta
Cepheus was discovered in October 1784 by you guessed it, John Goodricke.
This would be Edward Pigott’s last major astronomical
discovery in York. In 1785 with his father Nathaniel, they planned to be away
for around two years going back to France.
One area that Pigott did want to concentrate on was looking at stars
that he called suspect variables. These were stars that needed more
observations to confirm if they really did vary in brightness.
His next major contribution would be in 1795 after the death
of John Goodricke who died on 1786 and this observation would be made not from
York but from the city of Bath.
www.theramblingastronomer.co.uk
No comments:
Post a Comment