From a historical point of view, astronomy is one of the oldest natural and exact sciences, with observations and scientific explanations by various cultures dating back to early Antiquity.
Spherical or observational astronomy is the oldest branch of astronomy. Observations of celestial objects have been important for religious and astrological purposes, and for timekeeping and navigation.
Celestial Navigation has been used in position fixing and navigation by observing the positions of celestial bodies, including the sun, moon, planets and stars. Instruments such as sextants have been used since medieval times for measuring the positions of stars and the angular distances between celestial objects.
In short, what is known as the scientific revolution essentially started in the 16th century with the publication by Nicolaus Copernicus of his work about heliocentric astronomy in 1543. This was followed by the works, observations and ideas of other scientists and astronomers such as Tycho Brahe, Galileo Galilei, and Johannes Kepler, culminating with Isaac Newton’s work entitled Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), first published in 1687, which expounded his laws of motion and the law of universal gravitation, and established the discipline of classical mechanics.
Newton’s Principia historically had an indirect, albeit significant, influence on the progress of navigation and on related topics such as tide analysis and prediction.
Newton’s theory of gravitation first enabled an explanation of why there were generally two tides a day, not one, and gave hope for a detailed understanding of tidal forces and behavior.
Newton presented in the Principia his mathematical theory concerning tides and lunar motion, and it is known that sea travel was essential for trade to the British and other navigators, who needed to have a good knowledge of tidal cycles and patterns and how they affect navigation and the determination of longitudes.
In the 17th century, the creation of learned societies like the Royal Society in England under the patronage of the king and with the help of some known personalities, and the French academy of sciences by Louis XIV and his minister Colbert, was helpful in advancing the interest in scientific and astronomical research.
During the 18th and 19th centuries, the study of the three-body problem by Euler, Clairaut, and d’Alembert led to more accurate predictions about the motions of the Moon and planets. This work was further refined by Joseph-Louis Lagrange and Pierre Simon Laplace, allowing the masses of the planets and moons to be estimated from their perturbations.
The scientists and astronomers who came after Newton and continued or developed his work made additional contributions to the theory of tides. As an example, in 1776, Laplace formulated a set of linear partial differential equations, for tidal flow described as a barotropic two-dimensional sheet flow (this is a flow whose density is a function of pressure only). Laplace obtained these equations by simplifying the fluid dynamic equations.
Nathaniel Bowditch, regarded as the founder or one of the founders of modern maritime navigation, read Newton’s Principia as a young man, and then translated Laplace’s Mécanique céleste (Celestial Mechanics), a work that extended and completed Newton’s Principia and Newton’s theories.
Sometimes scientists and astronomers were helped or supported by the state, and sometimes they were helped by influential personalities. In addition to his contributions to mathematics, Carl Friedrich Gauss is also known for his contributions to astronomy and planetary theory, having among other things published a book or work entitled Theoria motus corporum coelestium in sectionibus conicis solem ambientum (Theory of motion of the celestial bodies moving in conic sections around the Sun). Gauss was financially supported during his years of study by the Duke of Brunswick.
Larger and more powerful telescopes were developed and built during the 18th and 19th centuries, contributing to the progress in observational and theoretical astronomy. One of the famous applications of astronomical theories and celestial mechanics around the middle of the 19th century was the prediction of the existence and position of planet Neptune, mainly by Urbain Leverrier, using only mathematics and astronomical observations of planet Uranus. Telescopic observations confirming the existence of a major planet (subsequently called or named Neptune) were made on September 1846 at the Berlin Observatory.
William Thomson (Lord Kelvin) applied Fourier analysis to the determination of tidal motion and to explain tidal phenomena in relation to harmonic analysis. As a practical application of the astronomical theory of tides and lunar theory (i.e. the theory of the moon’s motion as deduced from the law of gravitation with its perturbations), at the end of the 19th century Thomson and others conceived tide-predicting machines, which were special-purpose mechanical analog computers constructed and set up to predict the ebb and flow of sea tides and the irregular variations in their heights – which change in mixtures of rhythms, that never (in the aggregate) repeat themselves exactly. Their purpose was to shorten the difficult and error-prone computations of tide prediction. These machines provided predictions valid from hour to hour and day to day for a year or more ahead. They were widely used for constructing official tidal predictions for general marine navigation, and were viewed as of strategic military importance until the second half of the 20th century.
The image below shows the tide predicting machine by Sir William Thomson in 1876. This machine combined ten tidal components, one pulley for each component. It could trace the heights of the tides for one year in about four hours.
(Image source: https://en.m.wikipedia.org/wiki/File:DSCN1739-thomson-tide-machine.jpg )
Tide-predicting machines became generally used for constructing official tidal predictions for general marine navigation, and were viewed as of strategic military importance until the second half of the 20th century.
Important advances were made in astronomy during the 18th and 19th centuries due to observations as well as theoretical investigations and publications. These advances were accompanied or followed by applications related to navigation and nautical astronomy, sometimes stimulated or supported by societal and commercial interests or needs.
Progess in astronomical theory, research and applications continued during the 20th century in several directions.
In the late 19th century and most of the 20th century, astronomical images were made using photographic equipment. Modern images are obtained using digital detectors, particularly using charge-coupled devices (CCDs) and recorded on modern media.
Radio astronomy flourished mostly after the second half of the 20th century
The discovery of the cosmic microwave background radiation, regarded as evidence for the Big Bang theory, was made through radio astronomy.
Radio astronomy uses large radio antennas known as radio telescopes, that are either used singularly, or with multiple linked telescopes utilizing the techniques of radio interferometry and aperture synthesis.
Other observational branches of astronomy include infrared astronomy, x-ray astronomy, and ultraviolet astronomy.
Related fields or subfields of astronomy that were developed during the 20th century include astrophysics, astrochemistry, stellar astronomy, galactic astronomy, physical cosmology, astrobiology, …
Theoretical astronomy in the 20th century studied the existence of objects such as black holes and neutron stars, which have been used to explain such observed phenomena as quasars, pulsars, blazars, and radio galaxies. Physical cosmology made advances during the 20th century. In the early 1900s the model of the Big Bang theory was formulated, supported by cosmic microwave background radiation, Hubble’s law, and the cosmological abundances of elements.
Space telescopes have enabled measurements in parts of the electromagnetic spectrum normally blocked or blurred by the atmosphere.
Operational space telescopes orbiting Earth outside the atmosphere avoid light pollution from artificial light sources on Earth. Their angular resolution is often much higher than a ground-based telescope with a similar aperture.
The image below shows the Hubble Space Telescope, which was launched into low Earth orbit in 1990, and remains in operation in 2023:
(Image source: https://en.m.wikipedia.org/wiki/File:HST-SM4.jpeg )
During the 1990s, the measurement of the stellar wobble (or Doppler spectroscopy) of nearby stars was used to detect large extrasolar planets orbiting those stars.
Human missions and crewed spaceflights have been sent to explore outer space (until now mostly in the vicinity of planet Earth and to the Moon) since after the second half of the 20th century.
Interplanetary space probes have flown to all the observed planets in the Solar System as well as to dwarf planets Pluto and Ceres, and several asteroids. Orbiters and landers usually return more information than fly-by missions.
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