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Famous
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Aristarchus of Samos (c. 300- 250BC):
A Greek astronomer and mathematician who live from 310 BC to 230BC, was said
to have first proposed the heliocentric (the sun being at the centre of the
solar system) theory of the universe. The only writing of his that remains,
‘The Sizes and Distances of the Sun and Moon' followed highly original
procedures, however his calculation of the Moon’s distance was incorrect due
to the lack of accurate instruments, but had a more correct value of the
solar year. The writing does not mention his conclusion that the Earth moves
around the sun and that the sun is stationary, but statements by Archimedes
and Copernicus indicate that he held this theory. Another theory of his is
that the Sun is larger than the Earth, that the Earth rotates upon its axis
causing day and night and that the ecliptic axis of the Earth causes the
change of the seasons.
Hipparchus (c. 190-120 BC):
 Hipparchus lived from 190BC to 120BC and was the most important Greek
astronomer of his time. Born in Nicaea, Bithynia (modern day Iznik, Turkey),
Hipparchus was extremely accurate in his research, which is recorded in the
Almagest the scientific treatise by the astronomer Ptolemy who was greatly
influenced by Hipparchus. By comparing his studies with that of Earlier
astronomers, Hipparchus discovered the precession of the equinoxes
(elliptical orbit). His calculation of the tropical year (the length of the
year determined by the seasons) was within 6.5 minutes of modern
measurements. Hipparchus invented a method of locating geographical
positions by using latitudes and longitudes and also catalogued, charted and
calculated the brightness of up to 1000 stars. Hipparchus also compiled a
table of trigonometric chords that became the bases for modern trigonometry.
Nicholas Copernicus (1473-1543):
 Nicholas Copernicus was a Polish astronomer who set the foundation of
modern astronomy based on his system, the Copernican system. The Copernican
system was the first modern European theory of planetary motion that places
the sun at the centre of the solar system with all of the planets revolving
around it in perfect circles, as opposed to traditional Ptolemaic system
which stated that all of the planets and the sun revolved around the Earth.
This system was developed in the sixteenth century from the analysis of
ancient astronomical record however this particular theory of Copernicus,
was not received well in the church at all and so was suppressed after an
ecclesiastical trial. However, there still remained many followers of the
Copernicus system which gradually took over the original theory that the sun
and other planets revolved around the Earth.
Galileo Galilei (1564-1642):
 Italian astronomer, mathematician and physicist Galileo Galilei
contributed greatly to astronomy. With his construction of astronomical
telescope he enlarged the vision of human kind and enabled a new
understanding of universe. The astronomical telescope was constructed after
he heard a magnifying instrument being put together in Holland in 1609. With
this new instrument Galileo discovered that the surface of the moon is not
smooth but indeed an uneven, mountainous surface and that the Milky Way is
made up of numerous separate stars. The four largest satellites of Jupiter
were discovered in 1610, which were first satellites of the other planets
(excluding the moon and the Earth) to be detected. Due to his adherence of
the Copernicus system, he was forced to stand trial in the Vatican, publicly
renounce his views and spent the rest of his life under house arrest.
Johannes Kepler (1571-1630):
 Kepler’s laws were three mathematical statements created by the German
astronomer Johannes Kepler. His laws explain the revolution of planets
around the sun. The first law expresses that the orbit shape of the planets
is eclipse and the distance from the sun of each planet differs from another
as it shift through one orbit. The second law of Kelper states that as the
planets distance themselves away from the sun their speed decreases. The
third law conveys a relationship between the average distance of the planet
from the sun and the time to finish one revolution around the sun. Kepler's
first and second laws were published in 1609 in ‘Commentaries on the Motions
of Mars? The third law appeared in 1619 in ‘Harmony of the Worlds?
Sir Isaac Newton (1642-1727):
 Sir Isaac Newton could be considered as one of the greatest scientists
that ever lived. He formulated the theory of gravitation (as commonly
depicted after an apple fell on his head), and the discovery that white
light consists of multiple colour spectrums. These breakthroughs are
considered as significant contributions to astronomy and science as a whole.
His discoveries in terrestrial and celestial mechanics in his ‘Philosophiae
naturalis principia mathematica' published in 168 are one of the
fundamental highlights in science. The first part of principia is dedicated
to dynamics and his famous laws of motions.
Edmond Halley (1656-1752):
 Edmond Halley was an English astronomer and mathematician born in London
and educated in the University of Oxford. He was fascinated by the theories
of Isaac Newton and encouraged him to write the famous ‘principia' and also
published it at his own expense. Halley’s most important scientific work was
the ‘Astromiae Cometica Synopsis' which was published in 1705. This book
used Newton’s Law of motion to mathematically demonstrate that comets move
in elliptic orbits around the sun. He is famous for the prediction of the
return of a comet in 1758, now known as Halley’s Comet which validated his
theory that comets are a part of the solar system.
Sir James Hopwood Jeans (1877-1946):
 James Jean was an English mathematician, physicist and astronomer who lived
from 1887 to 1946, a professor of applied mathematics at Princeton
University (1905-1909), later lecturing at Cambridge and Oxford being
knitted in 1928. Devoting himself to mathematical physics he was involved in
the dynamical theory of astrophysics and cosmogony, later solving the
problem of the behaviour of certain nebulae, the origins of binary stars and
the evolution of gaseous stars (Problems of Cosmogony and Stellar Dynamics).
With Harold A. Jeffreys he developed a hypothesis of the origin of the
Earth. In 1929 Jeans abandoned research and became an outstanding
populariser of science and the philosophy of science, writing many works
including The universe around us (1929), The Mysterious Universe (1930) and
The Growth of Physical Science (1947).
Tycho Brahe (1546-1601):
 Danish astronomer, Tycho Brahe, was an
outstanding astronomer in the late sixteenth century. His improvement of
instruments and his nearly precise location of planets and stars made the
approach easier for future discoveries in that Kepler’s laws were developed
from Tycho Brahe’s observation of the planets. The various accomplishments
of Tycho Brahe include the first observation of supernova in the
constellation Cassiopeia in 1572 and the discoveries of the inclination of
the lunar orbits. Also in 1572 he was given funds by the Danish King
Frederick II to build a castle, Uranienborg (‘fortress of the heavens), and
an observatory, Stjarneborg, on the island of Hven. Frederick’s successor,
Christian IV withdrew Brahe’s benefits in 1688. Even so, in 1597 Brahe was
invited by to Bohemia by the Holy Roman Emperor; Rudolf II, who have him a
pension of 3000 ducats as well as an estate near Prague where a new
observatory could be built, however Brahe died in 1601 before his
observatory could be completed. Brahe never fully accepted the Copernican
system of the universe although he combined it with the old Ptolomeic System
as a compromise. In Brahe’s system, the five planets revolved around the
sun, which, with the planets, circled the Earth each year.
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