Kepler and his Remarkable Contributions to Astronomy in the 17th-century

-written by Radha Mittal, edited by Muskan Aggarwal

Born in December 1571, Johannes Kepler was a German astronomer, mathematician, astrologer, natural philosopher, and musician. He is a crucial figure in the 17th-century scientific revolution and is best known for his laws of planetary motion and his books Astronomia nova, Harmonice Mundi, and Epitome Astronomiae Copernicanae. This work also provided one of the foundations of Newton’s universal gravitational theory.

1610 Portrait of Johannes Kepler

He also taught mathematics in Linz and served as an advisor to General Wallenstein. In addition, he did essential work in the field of optics, invented an improved version of the refracting telescope (or Kepler) telescope, and was mentioned in his discovery of the modern Galileo Galilei telescope.

Kepler was the first person to publish a defence of the heliocentric model of Copernicus.

Johannes Kepler’s first major astronomical work, Mysterium Cosmology, was published in 1596. This study was primarily aimed at justifying the distance from the Sun in terms of six known planets and five regulars polyhedral. Mysterium was the first published defence of the Copernicus system. Copernicus proposed a heliocentric model in his famous work, De Revolutionibus orbium coelestium but relied on Ptolemy’s tools to explain changes in planetary orbital speeds, using the centre of the Earth as the reference for orbit. Mysterium is considered an essential task in astronomy because it has removed the remaining flaws in Ptolemy’s theory from the Copernicus system, despite the mistakes of its primary dissertation.

Kepler's Platonic solid model of the Solar System, from Mysterium Cosmographicum (1596)

His work Astronomia nova is considered one of the most essential books in astronomy. Kep1er presented a decade of research on the movement of Mars in his most famous work, Astronomia Nova. Apart from incorporating the first two of the three principles now known as Kepler’s Law of Planetary Motion, it insisted on the heliocentric theory. The idea that a planet moves in an elliptical orbit and its velocity changes with distance from the Sun was completely revolutionary at the time. Kep1er also discussed the gravitational pull of the Earth as well as magnetism. He thought this attraction interacted and was proportional to the body’s mass. However, he believed that gravity had a finite range and did not know how that force would change with distance. Thus, Kepler’s idea was quite different from the concept of gravity after Newton. Astronomia nova is a highly influential piece of the scientific revolution and is considered one of the most essential books in the history of astronomy.

Representation of the inverse-square law governing the intensity of light with S as light source

Johannes Kepler began studying the laws of optics in 1600, and in 1604 his work Astronomiae Pars Optica (the optical part of astronomy) was published. The book contains, among other things, the formulation of Kepler’s law that light intensity decreases with the square of the distance. A description of reflections from the plane and curved mirrors. The astronomical meaning of optical systems such as parallax, astronomical refraction, and the apparent size of celestial bodies. Astronomiae Pars Optica is considered the basis of modern optics. Another influential piece of optics by Kep1er, Dioptris, was published in 1611.

Camera obscura is a natural optical phenomenon that reverses when a light beam passes through a small aperture, and the inverted image is displayed on the screen opposite the opening. That is the principle that a pinhole camera works. Johannes Kepler first used the term “camera obscura” in his work Astronomiae Pars Optica in 1604.

He discovered that this is the principle behind the mechanism of pinhole cameras. Kep1er extended his work to the human eye and noticed that the image was flipped through the lens of the eye. His findings later helped explain physical phenomena such as central vision, visual field, dark adaptation, and refractive error.

Diagram of image formation in a human eye
Another important contribution by Kepler includes the three laws of planetary motions,

Kepler’s laws of planetary motion usually revolve around cycles, orbits, and regions of the planet and the Sun. Therefore, this principle shows that planets in the solar system centred on the Sun orbit the Sun in an elliptical orbit with the Sun at one focal point.

Based on this assessment of planetary movement, Kep1er introduced a set of laws commonly known today as Kep1er’s three laws. Kepler’s three laws describe the behaviour of a planet as a function of its orbit through the universe. The first two Kepler’s laws were published in The New Astronomy in 1609. Their discovery turned out to be a serious approach to the development of modern science.

First law

Known as the law of ellipses, this law explains that planets rotate around the Sun in orbit described as an ellipse. The first law of this Kepler is commonly known as the law of rotation. The law suggests that the trajectory of each planet with the Sun is an ellipse and that the Sun is in one of the two focal points of the ellipse. According to Kep1er, there is no doubt that the earth will rotate around the Sun, but not in a circular orbit, it revolves around the ellipse. The ellipse has two focal points. The Sun is one of the focal points of the ellipse.

Second law

Known as the law of equal area, this law defines the speed at which a particular planet rotates as it orbits the Sun. The speed at which planets rotate in space is constantly changing. Planets rotate fastest when they are closest to the Sun and slowest when they are farthest from the Sun.

Third law

Kepler’s third law, called the Law of Harmony, compares one planet’s orbital period and radius with that of another. Unlike Kepler’s first and second laws, which describe the kinetic attributes of a single world, the third law compares the kinetic properties of different planets.




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