The Famous ‘Five’ in Modern Astronomy

Nicholos Copernicus

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The foundations of Modern Astronomy were laid by Copernicus, Tycho Brahe, Kepler, Galileo and Newton.

Nicholos Copernicus

Nicholos Copernicus (1473 – 1543 A.D.) inaugurated a new era in astronomy by discarding the old belief in the geocentric motion of the sun and the planets. In his book ‘Revolution of the celestial bodies’, he explained the motion of the earth and other planets around the sun in circular orbits with the sun at the centre and also that of the moon around the earth in a similar orbit. He assumed that earth revolves around the sun once a year and rotates about an axis through its centre once a day from west to east.

Tycho Brahe

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Tycho Brahe

Tycho Brahe (1546 – 1601 A.D.) of Prague was a famous Swedish astronomer. He gave Tychonic system with stationary earth, the sun and moon moving around the earth and the planets moving around the sun. He could not see the different phases of Venus and Mercury. So he did not believe in the Copernican Theory of heliocentric motion. But he left behind him a collection of his observations which helped his successor Kepler for his excellent discoveries.

Johannes Kepler

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Johannes Kepler

Johannes Kepler (1571 – 1630) was the greatest German astronomer. He joined Tycho Brahe in 1600 and succeeded him as the Imperial Mathematician. After studying for two decades, he formulated his famous three laws of planetary motion. Kepler accepted Copernican theory of heliocentric motion of planets and established elliptical orbit of the planets around the sun. He tried one hypothesis after another to fit the observational data of his predecessor and finally arrived at his laws in 1618. Next year he published the three laws in his ‘Harmonics’.

Galileo Galilei

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Galileo Galilei

Galileo Galilei (1564 – 1642 A.D.) was the great Italian astronomer. He disproved the statement made by Aristotle 2000 years before that heavier body falls more quickly. He proved by dropping two bodies of different weights from the leaning tower of Pisa. Galileo believed in the Copernican Theory of heliocentric motion of planets. He was the pioneer of the telescope. With his telescope, he saw the planet Jupiter and its satellites and also the phases of Venus. He established the rotation of earth by experiments. He wrote a book ‘Dialogues on the Ptolemic and Copernican systems’ in which he supported Copernicus and challenged the ideas of Aristotle and Ptolemy. He was considered as enemy of the Church and was humiliated.

Sir Isaac Newton

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Sir Isaac Newton

Sir Isaac Newton (1642 – 1727) was the chief architect of Modern Astronomy. He was the pioneer of Dynamics and Calculus. He contributed a lot to Mathematics and Astronomy. Newton introduced his theory of universal gravitation. Every particle of matter in the universe attracts every other particle with a force that varies directly as the product of their masses and inversely as the square of the distance between them. This was a very brilliant idea and it explained how the sun pulls the planets and causes them all to orbit around it and how the earth pulls the moon and keeps it in its orbit. He explained his principle of universal gravitation and other Mathematical findings in his book ‘Principia Mathematica’.

Hats off to these great people.

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Comments 10 comments

Peter L. Griffiths 5 years ago

The main motive for Kepler's discoveries was to adjust the recorded observations to take account of Copernicus's discovery that the Earth as the observation point was not stationary but orbited round the Sun.


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Rubanraj 5 years ago from South India Author

Several astronomers tested Kepler's theory against astronomical observations. For instance, Pierre Gassendi observed the transit of Mercury in 1631 and confirmed Kepler's prediction. Thank You, Peter.


Peter L. Griffiths 5 years ago

Further to my previous comment, two of Kepler's laws are stated in the Introduction to Astronomia Nova(1609), these are that the velocity of the planets is inversely related to their distance from the Sun, and that planetary orbits are elliptical. Greater mathematical precision was given to these discoveries in Kepler's later works and also the important concept of the foci.


Peter L. Griffiths 5 years ago

Further to my previous comments, Galileo's law of falling bodies v^2=d can be reconciled with Kepler's inverse square law v^2=1/r as

v^2=d=1/r, let L indicate a small change then we have

v^2+Lv^2=d+Ld=1/(r-Ld). This is the usual method of measuring velocity. For the reciprocal method of measuring the same velocity we have

v^2+Lv^2=r+Lr=1/(d-Lr). The same velocity can be measured as distance per unit time or time per unit distance, one method is the reciprocal of the other. There are only three variables, distance, time and velocity. d+r equals the major axis of the elliptical orbit.


Rubanraj profile image

Rubanraj 5 years ago from South India Author

Thank you Peter for adding more comments.


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andrebreynolds 5 years ago

They are all the BIGGEST names I've ever known when talking about astronomy.


Peter L. Griffiths 4 years ago

Kepler's area law for time taken can be initially compared with the area of a right angle isosceles triangle t=rXrX(1/2). Let the (1/2) become a power and we have t=rXr^(1/2) which is Kepler's distance law v=r/t=1/r^(1/2) which applies throughout the whole universe.


Peter L. Griffiths 3 years ago

Further to my previous comments, the connection between Galileo's v^2=d at the empty focus end of the elliptical orbit and Kepler's v^2=(1/r) at the Sun focus is mathematically very interesting and not at all straight forward. Kepler's version can be adapted for further research purposes by including the constant V being the maximum velocity, then the variable velocities can be expressed as V/#r where # is my notation for square root. In this way the same velocity arises on both the accelerating side as well as on the decelerating side, but in opposite directions. As one of the properties of all perfect ellipses d is the distance from the curve to the empty focus, and r is the distance from the curve to the Sun focus, d+r equals the major axis of the elliptical orbit.


Peter L. Griffiths 2 years ago

There is a little known paper by Kepler Concerning Conic Sections included in his book on Optics published in 1604. This paper is full of mistakes originating from the works of Apollonius of Perga and Eutocius of Ascalon who were trying to unify the theory of the 5 conic sections, the straight line, the circle, the ellipse, the parabola and the hyperbola. Kepler thought that his newly discovered concept of the focus would help in this, particularly his recognition that pins and thread applied to foci might help in constructing the conic sections. It was not until 1618 that Kepler recognised that the location of the Sun was at a common focus for the orbits of the planets.


Peter L. Griffiths 2 years ago

Isaac Newton's Inverse square law is Newton's unsuccessful attempt to divide Kepler's Distance Law v^2 =1/r by Galileo's Law of Falling bodies v^2 = r to obtain the centripetal force of F =1/r^2. Unfortunately Newton fails to recognise that in Kepler's distance law, the distance r is the distance from the Sun focus, whereas in Galileo's law of falling bodies the distance r is distance from the Empty focus, so that the quotient should be F =1, not 1/r^2.

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