GCSE Astronomy

Astronomers

Most of the information here is for background information rather than for the GCSE exam. You would be expected to know the discoverers of planets and be aware who Galileo and Isaac Newton were, for example.

Aristarchus   of Samos. 3rd. Century BC. Usually receives a mention as possibly the first person to seriously suggest that the Earth orbited the Sun and attempted to put it on some sort of scientific footing.

Friedrich Bessel  

Based in Königsberg, in 1838 he made the first parallax measurement of a star - 61 Cygni, which he established to be about 11 light years away (this was also the first scientific proof of the heliocentric theory).

He noted that Sirius was wobbling (as we now know, due to the effect of a White Dwarf companion). In the last two thousand years, Sirius has moved about three-quarters of a dregree and Bessel was the first to note that it was not moving in a straight line.

Tycho Brahe  Inspired to become a 'professional' astronomer by the supernova of 1572. He was actually an anti-Copernican and, with the assistance of the King of Denmark, worked initially in his own observatory on the island of Hven, in the Baltic (between 1576 and 1597). He observed a supernova in 1572 and did pioneering work on the Great Comet of 1577. He left Denmark after a 'falling-out' with the new King in Denmark, and from 1599 he worked in Prague as Imperial Mathematician to the Holy Roman Emperor, Rudolf II. He died unexpectedly in 1601, bequeathing his work to Johannes Kepler, who unfortunately used his data to promote the Copernican theory (unfortunately for Brahe's aims, that is). Tycho's catalog contained about 1,000 stars.

Annie Jump Cannon   Became an assistant to Edward Pickering at Harvard Observatory in 1896. Cannon re-jigged the Harvard classification system to produce the one we know today. Her spectral analysis of stars resulted in the completion of the Henry Draper Catalog (1918-24) classifying 225,000 stars. This was extended later.

Giovanni Cassini   first director of the Paris Observatory who discovered the main gap in Saturn's rings - the Cassini Division.

He was born in Perinaldo, near Nice, in present-day France but then Italian. At 25 he became Professor of Astronomy at the University of Bologna. Cassini established his reputation through his observations of the motions of comets and the apparent motion of the Sun. He used the most advanced telescopes of his day to observe the satellites of Jupiter and to draw up accurate tables of their movements. These theoretically allowed sailors to find their longitude (but was usually impractical) but seems to have been of genuine use to mapmakers. He discovered the seasonal changes on the planet Mars and measured the period of rotation of both Mars and Saturn. In 1669 he went to Paris to help with the setting up of the new Paris Observatory, and later became its director. There he discovered four satellites of Saturn - Iapetus (1671), Rhea (1672), Dione (1684), and Tethys (1684) and observed the gap in the planet’s ring system. He measured the distance of Mars from the Earth using observations of parallax, which enables the distances of all the planets to be more accurately calculated.

He was a late and only partial convert to the Copernican system and never accepted Newton's Theory of Universal Gravitation. He rejected the idea of the finite speed of light which his own observations of Jupiter’s satellites had revealed (and which had been calculated by one of his assistants, Olaus Romer) and he persisted with an idea of the Earth’s shape that had been proved to be incorrect. Cassini went blind in 1710 and died in Paris in 1712. Three further generations of Cassinis headed the Paris Observatory after him.

Nicolaus Copernicus   Polish astronomer from Torun who is credited with strongly pushing the idea of a Sun-Centered theory for the planetary system. His ideas were published in his book De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres), just before his death in 1543. According to the Protestant reformer Martin Luther, Copernicus was "this fool who wants to reverse the science of astronomy", although his book had been published by a Lutheran in Nürnberg (Nuremberg). Whether Luther actually said this is open to dispute (and if he did, whether he said it tongue in cheek). A preface was added to the book by Andreas Osiander to the effect that the ideas expressed in the book were a hypothetical mathematical exercise and did not represent physical reality. Giordani Bruno said that this preface "could only have been written by one fool for the benefit of other equally ignorant fools". This was just before they burnt him at the stake. The idea of describing scientific theories as 'hypothetical' still exists in parts of 21st century America.

At the time, scientific evidence in support of Copernicus was thin on the ground. The benefits of his theory were

• The planetary ordering was regular in the sense that the planet with the shortest period was closest to the Sun, and the periods of each planet increased as you went outwards from the Sun

• It provides an elegant explanation as to why Mercury and Venus are never seen too far away from the Sun

• It explained retrograde motion

• It explained why the brightness of planets varied.

• It was more elegant to have just the earth rotating rather than having the entire heavens rotate.

• It did away with a major defect of the Ptolomaic system which stated that the size of the Moon should vary considerably

Its disadvantages were

• The Earth was moving along at a fantastic speed about the Sun

• There was no obvious way that the Earth could also be draging the Moon along with itself

• As the Earth moved around its orbit, there should be a noticeable parallax of the stars, which didn't happen (e.g. bearings to the stars should be noticeably different when at one extreme of their orbit compared with those taken six months later when the Earth was at the opposite end of its orbital path).

• The inhabitants of Earth would be thrown off at a tangent because of the Earth's rotation, not going about their day-to-day business in blissful ignorance of how fast they are moving.

• It posed more questions than it answered

• It conflicted with straightforward common sense!

John Flamsteed

First Astronomer Royal, who established the observing program at Greenwich Observatory.

Williamina Fleming

Josef Fraunhofer

Galileo Galilei   is credited with making use of the just-invented telescope to discover

• that Jupiter had moons (the Galilean satellites)
• that the Milky Way could be resolved into individual stars
• to observe spots on the Sun.
• that Venus went thru phases analogous to the phases of the Moon.
• to observe the moon, where he saw mountains and craters.

These discoveries were announced in The Starry Messenger in 1610.

1632 saw the publication of Dialog on Two World Systems and 1638 Two New Sciences.

He was also persecuted for his beliefs, most notably the idea that the Earth revolves around the Sun, and this persecution took place when circumstanial evidence for the Copernican system was fairly well established. In 1631, at the age of 70, he was hauled before the Inquisition. In the end, Galileo did recant his beliefs rather than suffer death and/or torture and was confined to his villa in Arcetri for the rest of his life, where he was forbidden from writing any scientific publications (or making contact with Proddys). Bertolt Brecht wrote his Galileo to show the parallels between the way that people (didn't) think in Galileo's time and the way they (don't) think today.

Some sources attribute the severity of the actions against Galileo as being due to the effects of the Thirty Years War. On the other hand, the specific 'instruction' about not spreading the Copernican System, which the Inquisition claimed Galileo had defied, stemmed from 1616 - before the war started. And well before this, in 1600, Giordano Bruno had been burned at the stake for preaching Copernicism.

John Goodricke

Made the first systematic study of Algol in conjunction with his colleague Nathaniel Piggott. It appears it could have been Pigott who first suggested that Algol could be an eclipsing binary, although when the details were published, he allowed Goodricke to be the sole author. It also appears that the pair eventually rejected this explanation (although it is the true explanation) as a result of other discoveries they made. For example, β-Lyrae as well the discovery of β Aquila by Pigott followed closely by δ Cephei by Goodricke (in 1786), these two latter stars being the first Cepheid variables to be discovered. It is usually noted that Goodricke was deaf and dumb. Unfortunaterly he died very young, from the effects of the cold while observing if the usual stories are to believed.

Edmund Halley

Second Astronomer Royal. Discovered that several stars had shifted their position since the time of Ptolemy. See Halley's Comet

Thomas Harriot

Believed to have used a telescope to view sunspots and the Moon prior to Galileo, although never published his findings at the time. This would have been about 1608. His observations of 'Halley's Comet' were to prove extremely useful to Halley himself later on.

Caroline Herschel

Sister of William who seems to have been an active partner in many of William's observations in Britain. She continued working in astronomy in their hometown of Hannover, after William's death. She discovered eight comets.

John Herschel

Son of William Herschel. The first to undertake a really detailed survey of the stars in the South. From 1832 to 1838 he carried this work out at the Cape.

William Herschel

German astronomer who discovered Uranus while living in Bath. As a rsult of this discovery he was taken into the employment of King George III and moved eventually to Slough. He also discovered Titania and Oberon (moons of Uranus) and Mimas and Enceladus (moons of Saturn). His sister, Caroline, seems to have been an active partner in William's observations.

In 1803, he discovered that Castor was a binary star.

He made a systematic search of visual double stars and showed that most of them were physical pairs, rather than close together because of our line of sight.

Ejnar Hertzsprung   Qualified as a chemical engineer before convering his interest in astronomy into a full-time job. Allegedly the last person to have become a Professor of Astronomy despite no formal training in the subject. The origins of the Hertzsprung-Russel diagram date from 1905.

Hipparchus   Second Century BC. Originally classified all stars from first to sixth magnitude (this was formally put on a more scientific basis in 1856). Although his original star catalog has been lost, it has come down to us via Ptolemy. Using information from a solar eclipse visible in the Near East, he was able to derive an accurate measure of the distance to the Moon. He discovered precession and he also realized that a day of 365.25 days was too long for the current calendar.

Jeremiah Horrocks

See Jeremiah Horrocks.

Edwin Hubble

Trained as a lawyer and did actually work briefly in the profession. before becoming an assistant at Yerkes Observatory. After gaining a Ph.D in 1917, he served in the Army for two years before taking up a post at Mout Wilson in 1919, at the age of 30. Among the 'human-interest' aspects is the apparent fact that he was offered the possibility of turning professional as a heavyweight boxer.

In the early 20s he was able to show the existence of galaxies external to our own and by the end of the decade he had shown that the Universe was expanding (as predicted by Alexander Friedmann using Einstein's Equations, but not predicted by Einstein himself).

Milton Humason

Worked as a mule driver during the construction of Mount Wilson. From this he obtained a job as caretaker at the new observatory. In 1919, he became an assistant at the Observatory despite any formal training and worked with Hubble on his work showing the expansion of the Universe.

Christaan Huygens   Famous for inventing a successful pendulum clock, he also developed telescopes which he used to discover Titan, the main moon of Saturn, and to identify the peculiar feature of Saturn as being due to rings.

Johannes Kepler   worked under Tycho Brahe in Prague and inherited Tycho's results (and his position of Imperial Mathematician) and used these results to deduce his laws. See Kepler's Three Laws.

His first two laws appeared in 1609 in New Astronomy, so by the time of Galileo's struggle with the Church, about 100 years after Copernicus' ideas were first made known, there was a considerable amount of evidence supporting Galileo's stance. Kepler supported and confirmed Galileo's work. Galileo expressed his appreciation to Kepler: "I thank you because you were the first one, and practically the only one, to have complete faith in my assertions".

In 1611, Rudolf was overthrown and events caused Kepler to move and take up a post as mathematics teacher in Linz (although he retained his title of Imperial Mathematician). He was still charged with working on the Rudolphine Tables, even when Rudolf died in 1612. He was still required to reside in Linz though and during the Thirty Years War which started in 1618, his mother was accused of witchcraft and he took up her defense at great expense in time and money to himself.

Nevertheless, in 1619 his Epitome, defending Copernican theory, appeared and was placed on the index of forbidden books by the Catholic Church.

His third law also appeared in 1619, in Harmony of the Worlds.

In 1627 he his Rudolphine Tables finally appeared, 1000 copies being prined (compare with the 300 copies of Newton's Principia). These table allowed the first observation of a transit of Mercury, but unfortunately the year after Kepler died. Gassendi observed this transit from Paris in 1631. It is claimed by some sources that Kepler's immediate influence was less than the 'popular' sources would have us believe. Jeremiah Horrocks appears to a near-contemporary who took an interest in his results (and modified them).

Henrietta Swan Leavitt

Urban Leverrier

Theoretically predicted the existence of Neptune. Berlin Observatory, operating on his predictions, found the planet in 1846. Further information by following this link.

Simon Marius

The subject of a charge of plagiarism from Galileo for his claims concerning observations of Jupiter and its moons. in any case, the names used for the four large satellites are his. In 1612, he has also observed M31 with a telescope.

Isaac Newton Universal Law of Gravitation Reflecting Telescope presented to Royal Society in 1672

Cecilia Payne-Gaposchkin,   British-born astrophysicist. Known for her study of variable stars, she was also the first astronomer to measure by means of spectral analysis the relative abundances of chemical elements in a star. She was the first to show that more than 60 per cent of the known galactic novas in the Milky Way are concentrated in the quadrant containing the galactic centre. She joined the Harvard University Observatory in 1923 and was granted a doctorate in 1925 from Radcliffe College. In 1938 she was named Phillips Astronomer at Harvard University, and in 1956 she became Professor of Astronomy. At Harvard she developed a new method for determining stellar magnitudes from photographic plates.

Ptolemy   produced the Almagest around 150 B.C. describing the common-sense Earth-centered Universe, which held sway for centuries. Orbits are perfect circles and 'stangely-moving' objects like the planets and the Moon move on epicycles.

Ole Romer   measured the speed of light from observations of the eclipses of Jupiter's satellites by the shadow of the planet. He was made Director of Copenhagen Observatory in 1681 and invented the Transit Circle and the Meridian Circle.

Slipher receding nebulae in 1912. at Flagstaff Observatory in Arizona.

Clyde Tombaugh