Astrophysics

Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. The study of cosmology is theoretical astrophysics at the largest scales.

History

Although astronomy is as old as recorded history, it was long separated from the study of physics. In the Aristotelian worldview, the celestial pertained to perfection—bodies in the sky being perfect spheres moving in perfectly circular orbits—while the earthly pertained to imperfection; these two realms were seen as unrelated.

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For centuries, the apparently common-sense view that the Sun and other planets went round the Earth went unquestioned, until Nicolaus Copernicus suggested in the 16th century that the Earth and all the other planets in the Solar System orbited the Sun. Galileo Galilei made quantitative measurements central to physics, but in astronomy his observation did not have astrophysical significance.

Related Topics:
Sun - Planet - Earth - Nicolaus Copernicus - 16th century - Solar System - Galileo Galilei

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The availability of accurate observational data led to research into theoretical explanations for the observed behavior. At first, only ad-hoc rules were discovered, such as Kepler's laws of planetary motion, discovered at the start of the 17th century. Later that century, Isaac Newton, bridged the gap between Kepler's laws and Galileo's dynamics, discovering that the same laws that rule the dynamics of objects on earth rules the motion of planets and the moon. Celestial mechanics, the application of Newtonian gravity and Newton's laws to explain Kepler's laws of planetary motion, was the first unification of astronomy and physics.

Related Topics:
Kepler's laws of planetary motion - 17th century - Isaac Newton - Celestial mechanics - Gravity

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After Isaac Newton published his Principia, maritime navigation was transformed. Starting around 1670, the entire world was measured using essentially modern latitude instruments and the best available clocks. The needs of navigation provided a drive for progressively more accurate astronomical observations and instruments, providing a background for ever more available data for scientists.

Related Topics:
Principia - Navigation - Latitude - Clock

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At the end of the 19th century it was discovered that, when

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decomposing the light from the Sun, a multitude of spectral lines were observed (regions where there was less or no light). Experiments with hot gases showed that the same lines could be observed in the spectra of gases, specific lines corresponding to unique chemical elements. In this way it was proved that the chemical elements found in the Sun (chiefly hydrogen) were also found on Earth. Indeed, the element helium was first discovered in the spectrum of the sun and only later on earth, hence its name. During the 20th century, spectrometry (the study of these spectral lines) advanced, particularly as a result of the advent of quantum physics that was necessary to understand the astronomical and experimental observations.

Related Topics:
Spectral line - Chemical element - Hydrogen - Helium - Hence - 20th century - Spectrometry - Quantum physics

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See also:

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• Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure
• Timeline of white dwarfs, neutron stars, and supernovae
• Timeline of black hole physics
• Timeline of gravitational physics and relativity