This is a story of a young man named John Goodricke who is credited with the introduction of a new branch of astronomy – the astronomy of variable stars. What are variable stars? We see hundreds of stars twinkling in the night sky. But what is not noticed is that these stars periodically change in brightness or magnitude. In 1783, Goodricke observed that the brightness of a star called Algol varies. Until this time, astronomers had busied themselves only in the study of the sun, the moon, planets, the moons of the planet Jupiter and the comets. Though a few astronomers had spent time in recording the exact position of stars in the sky, stellar astronomy or the study of stars was still in its infancy.
John Goodricke was born on September 17, 1764, in Groningen, the Netherlands. His father Henry, was a diplomat and his mother was the daughter of a wealthy Belgian merchant. When he was only five years old, John suffered from scarlet fever and lost his hearing ability. This was the time in England when the deaf and dumb people were derided by society. But the Goodrickes were an intellectual and educated family. Some of them also were well-placed in the Court of the King. Hence, John was sent to a renowned school for the deaf and dumb in Edinburgh. Here John learned the three ‘r’s of education – reading, writing and arithmetic. He also overcame his disability and learnt to speak and lip-read. Having conquered his handicap, he joined the Warrington Academy in 1778 which was a prominent educational institution known for its emphasis on the study of ‘natural philosophy’ or today’s science and mathematics. Here John’s interest in astronomy developed and he started night sky observation at the age of fifteen.
Young John’s neighbor in York, Nathaniel Pigott was an astronomer and had built a private observatory. It was one of the finest observatories of those times. Nathaniel’s son, Edward, too had a keen interest in astronomy and even though he was eleven years older than John, both became good friends.
In 1778, during his study of the stars, Edward noticed that the positions of stars and their brightness varied from one star catalogue to the other. He could attribute the change in the position to an error in observation or calculations but the difference in the brightness of these stars was to his mind an observation that required further study. Four years later, John and Edward decided to do collaborative research on the observations of stars which are variable or are perceived to be so.
The first star on their list was the second brightest star in the Perseus constellation Beta Perse, also known as Algol. Their studies revealed that Italian astronomer Geminiano Montanari, in 1672, had recorded that the star had changed its brightness. The name Algol is derived from its original Arabic name raʾs al-ghūl : or head (raʾs) of the ogre (al-ghūl) and it is believed that ancient Arabic astronomers attributed the changing brightness of this star to an act of a demon.
On 12 November 1782, John Goodricke recorded in his journal, “This night I looked at Beta Persei (Algol), and was much amazed to find its brightness altered … I observed diligently for about an hour – I hardly believed that it changed its brightness because I never heard of any star varying so quickly in its brightness.” As a true scientist, he first thought that this could be due to any of the three reasons – an optical illusion, a defect in his own eyes or even bad weather conditions.
He continued observing the star on every clear night and by April 1783, he could determine that the star’s brightness changed periodically in 2 days and 21 hours. He reported his observations to Anthony Shepherd, professor of astronomy at Cambridge. His friend Edward, in turn, notified it to Nevil Maskelyne, the Astronomer Royal and to William Herschel. The observations were quickly confirmed by Herschel.
John Goodricke also made a theoretical interpretation of the periodic variations of the star, Algol. He suggested that a ‘larger body’ possibly a planet revolved around Algol. It was observed that every time this body came between the earth and the star, it diminished the brightness of the star. Another interpretation could also be that the star had a region with cooler temperatures on its surface and every time this region faced the earth, the brightness was reduced.
This was a sensational scientific discovery of the time for which John was awarded the coveted Copley Medal of the Royal Society of London in August 1783. It was also proposed to elect him as a member of the Royal Society. Unfortunately, John was only nineteen years old at that time and could not be made member of the Society, for as per the rule of the society he had to be twenty one years of age. He was eventually elected member on 6 April 1786. But sadly, before the news could reach him at York, he had died of pneumonia on 20 April.
Edward Pigott remained John’s friend till the end and even though he never received any recognition for the work he carried out with John, he had no resentment. It is known from the journals of both Edward and John that they held each other in high esteem. After the star Algol, the duo together discovered a few more variable stars.
Modern observations have confirmed that Algol is actually a two-star system. When the cooler and less brighter star comes between the earth and the brighter star, we observe a drop in its brightness. Algol is favorably placed for observations during November every year.
Today, the study and observation of variable stars and the interpretation of the cause of these variations in their brightness is the most popular branch of astronomy among professional and amateur astronomers.
Visit these links for observing Algol 1. Minima of Algol 2, Beginner’s guide to estimate magnitude of Algol
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