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Caroline Herschel - 18th Century Female Astronomer
Caroline Lucretia Herschel was a German-British astronomer. With the help and support of her brother, an accomplished astronomer himself, Sir William Herschel she was trained in mathematics and astronomy. His tutelage helped her achieve prestige as a woman astronomer, respected and trusted by her peers. The Herschel siblings observed and documented many objects through the telescope together, thus contributing much to our knowledge of the heavens. Caroline Herschel also made some of the most important discoveries in her time working on her own.
Caroline Herschel was the first female astronomer to discover a comet, Comet C/1786 P1 (Herschel), objects in space that pass through our solar system and can be observed from Earth as bright moving heavenly bodies with a tail. It was the first of many. In 1832, her discoveries in the field of astronomy were honored by the King of Denmark honors with a medal. On her 96th birthday in 1846, Caroline Herschel was awarded the Gold Medal for Science by the King of Prussia. She received numerous recognitions for her work in astronomy, including the Gold Medal of the Royal Astronomical Society in 1828. She was named an Honorary Member of the Royal Irish Academy in Dublin in 1838, and three years before that she was named an Honorary Member of the Royal Astronomical Society in Britain. Herschel and Mary Somerville were the first women to be accepted into this prestigious organization.
"The eyes of her who is glorified here below turned to the starry heavens." Caroline wrote these words herself, and they were eventually etched on her tombstone. She died in January 9, 1848 at the age of 97 after living a full and productive life. Here is her story.
Caroline Herschel was born on March 16, 1750 in Hanover, Germany. “Lina” was the fifth of six children. When Caroline was three years old, she has smallpox, which left her left eye disfigured. When she was ten years old, she had Typhus, which led to stunted growth and in adulthood, she only grew to a height of 4'3".
Her father, Isaac Herschel was a gardener who played the oboe in the Prussian Army. Lina’s father wanted all his children to be trained in Mathematics, French, and music. All were given equal opportunities, except for frail Lina. Her mother, Anna Ilse Moritzen disapproved of her having an education. Her mother had simple plans for her. She thought educating Caroline was unnecessary because she would never marry and would be better off serving as a house servant. Fortunately, her father gave her rudimentary education, nonetheless. However, as fate would have it, Caroline spent her young life as a scullery made.
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From Germany, Caroline Herschel moved to Bath in England in 1722 when she was 22 years old. This was a few years after her father passed away. Freidrich Wilhelm (William) Herschel took in his sister who was not married. She served as his housekeeper while William established himself to be an accomplished music teacher in Britain. Caroline received music lessons from her brother during her free time. It paid off because Caroline became a highly regarded vocalist, recognized for her talent by England’s opera houses, though she would sing only when William was the conductor.
The siblings shared an interest in astronomy as well. William made Caroline his assistant when he started observing the night sky. William taught his sister Science and Mathematics, continuing the education that was started by their late father. She tended to him and the household while she spent grueling hours grinding glass for his telescope and making observations. Caroline made the complex calculations while her brother trained his telescope at the heavens and made detailed observations. His efforts paid off when in 1781, William Herschel made a very important discovery—the seventh planet of the solar system, Uranus. Since then, William Herschel devoted himself to the study of astronomy.
The brother and sister team worked tirelessly together to catalogue deep sky objects. Aside from their work on stars, comets, and nebulae, the Herschel siblings cemented their place in the history of astronomy for their discovery of Enceladus, one of the moons of Saturn, the ring planet.
Caroline was trained as her brother’s assistant, but she also made her own observations on the telescope when he is away. She discovered a nebula on February 26, 1783, an open cluster known at present time as NGC 2360.
The comet that she discovered in August 1, 1786, C/1786 P1, was dubbed, “first lady's comet” and with it, she secured her own place in the annals of the history of astronomy. The object that she saw was slow moving and traveling across the night sky. She saw it again the following night. She immediately informed other astronomers so that they too can study its path. Caroline Herschel’s discovery also secured her future. She became financially independent when in 1787 King George III declared that she would be paid a modest fee for being her brother’s assistant. She was the first woman to be paid for services of a scientific nature.
After her employment, Caroline devoted her time to astronomy, and made many important discoveries in the next few years. William gave her a telescope for her own use. When William decided to marry in 1788, Caroline had more time for astronomy, since she was freed from doing household duties. She discovered Comet Herschel-Rigollet (35P) on December 21, 1788, Comet C/1790 A1 on January 7, 1790 and Comet C/1790 H1 on April 18 of the same year. One year afterwards, she made another discovery. On December 15, 1791, she discovered Comet C/1791 X1. In October 7, 1793, Caroline discovered Comet C/1793 S2 (Messier), named after another astronomer who sighted it first, and sighted Comet 2P/Encke on the 7th of November, 1795. Caroline made another new discovery in August 14, 1797 with Comet C/1797 P1 or Comet Bouvard-Herschel.
Two years afterward, in 1799, the Royal Society in England decided to publish the star catalog that she had made. The first Astronomer Royal of the United Kingdom, John Flamsteed compiled the catalog that she used as reference. She painstakingly cross-indexed the existing catalog and added more than 550 new stars. Caroline Herschel also discovered 14 nebulae that were all previously unidentified. One of her most prominent discoveries in this area is the companion to Andromeda Galaxy, which is NGC 205.
In 1822, William died and Caroline decided to return to the country of her birth—Germany. She continued working on her catalogs, two of which are still being used by modern astronomers today.
Comet C/1786 P1 (Herschel)
The first discovery made by Herschel happened when the sky conditions were poor. Thus, the first observation could not be ascertained, and so confirmation was needed the following night. The comet was discovered at a magnitude of around 7.5 on the eve of August 1, 1786. The comet was first seen by the naked eye on the August 7, and observations continued to be possible until the month of October. Based on calculations made it was estimated that the perihelion (the point in a comet’s orbit where it is at closest approach to the Sun occurred earlier on July 8 at 0.41 AU.
This discovery occurred two years after Caroline’s first comet. It was near Beta Lyrae, with a parabolic orbit. Calculations showed Comet 35P/Herschel-Rigollet was as perihelion a month earlier on November 21 at 0.75 AU. One hundred and fifty-one years later, a comet was discovered on July 28, 1939 by Roger Rigollet of France. It was later confirmed from orbital calculations made by another astronomer that this was not a new comet, but rather the same one that was identified by Caroline Herschel on December 21, 1788. The name 35P refers to the the comet being the 35th periodic comet to be seen returning to perihelion. This new system was introduced in the year 1995.
Comet C/1790 A1 (Herschel)
On January 7, 1790, Caroline discovered another comet—her third. This new comet was not as observable as the other comets that she previously discovered, and few details were determined about it, except for its brightness of seventh magnitude. Perihelion was estimated to be at a distance of 0.76 AU on January 15.
Comet C/1790 H1 (Herschel)
The year 1790 was a fortuitous one for Caroline Herschel. After her discovery in January, she identified another comet on April 8. At first, its tail was not visible and only became evident by the month of May. Perihelion occurred on May 21, 1790 at 0.8 AU and nearest Earth approach happened in the early days of June at 0.7 AU.
Comet C/1791 X1 (Herschel)
The next comet that Caroline Herschel discovered broke a 20-month hiatus during which time not one new comet was identified. According to Caroline, the comet she discovered on December 15, 1791 was a telescopic comet that is “pretty large,” as Herschel described it. It was last seen on January 28, and perihelion occurred on January 14.
Comet C/1793 S2 (Messier)
A fifth magnitude comet discovered a comet on October 7, 1793, which was sighted earlier by astronomer Charles Messier on September 24. The comet was thus named after Messier. Perihelion occurred at rather close 0.4 AU on the fifth of November.
Caroline Herschel saw another comet on November 7, 1795, which was visible to the naked eye. Its perihelion occurred on December 21 and it was observable for three weeks. Many astronomers trained their telescopes at the comet and its orbit was calculated, although no definitive results came about. It was eventually determined that the comet was the same object that was observed in 1786 by Pierre Mechain. After the 1795 sighting, the comet was seen again on October 19, 1805. German astronomer Johann Encke was the person who made the calculations and determined that these comets were the same phenomenon. Encke’s declaration that the comet was a periodic comet was proven when it returned on 1822 just as he predicted. Because of this, the comet was named after him. It was the second comet in the history of astronomy the return of which was accurately predicted. Edmond Halley accomplished the first correct prediction of a comet’s return with the comet that now bears his name.
Comet C/1797 P1 (Bouvard-Herschel)
The last comet on Caroline Herschel’s impressive list of accomplishments was discovered on August 14, 1797. The comet was named after Herschel and Eugene Bouvard, the two astronomers that spotted it first. Two astronomers discovered a third magnitude comet independently and within just a few hours. The next night, it was visible to the entire community of night watchers—a bright object in the night sky. Two days after its discovery, the comet passed very near to earth, at only 0.0879 AU. When it was discovered by Herschel and Bouvard, it was passing at a distance of 0.17 AU. The comet was significant for being ranked 13th in terms of the distance of its orbit from the Earth. By comparison, the closest approach is credited to Comet Lexell, which reportedly passed the Earth at only 0.0094 AU in 1491. Calculations there were more reliable and accurate were made on July 1770, which pegged the distance
Caroline Herschel lives on
In recognition for her tremendous contributions to astronomy, both as an assistant to her brother, and as an astronomer in her own right, the scientific community honors Caroline Herschel by immortalizing her name. Aside from the comets that bear her name, there is a crater on the moon called “C.Herschel” and an asteroid (Asteroid 281) discovered in 1888 that is named, “Lucretia.”
Caroline Herschel was a pioneer. Deprived of a formal education and limited by poor health in her early life, she accepted the role that her mother assigned to her, but she took the opportunity to better herself when she was given the chance. She was ahead of her time, making discoveries about heavenly objects, detailed observations, and producing painstakingly complex mathematical calculations by hand. For hundreds of years she was an inspiration for female astronomers, and held the record for having the most comet discoveries until Carolyn Shoemaker usurped her in the 1980s. We can take inspiration from the amazing journey and long productive life of this strong woman and accomplished astronomer.
Lemonick, Michael. The Georgian Star: How William and Caroline Herschel Revolutionized Our Understanding of the Cosmos. W.W. Norton & Company. 2009.