Astrophysics is the domain of astronomy that uses the principles of chemistry and physics to discover the nature of the heavenly bodies. This subject does not talk about the position and motion of the heavenly bodies. Astrophysics mainly focuses on the galaxies, sun, extra solar planet, the interstellar medium etc. The emissions from these celestial bodies are examined all parts of the electromagnetic spectrum and density, luminosity, temperature and chemical composition are the properties explored. Astrophysics is a very vast subject therefore astrophysicists have to apply many disciplines of particle physics quantum mechanics, statistical mechanics, thermodynamics etc.
Astronomy is very ancient. Its different from the study of terrestrial physics. According to Aristotelian world view, the bodies in the sky are spheres whose only motion was uniform in a circle contrary to it earthly world is defined with growth and decay in which natural motion is in a straight line and ends when the moving object reaches its goal therefore it was firmly believed that matter in celestial region is fundamentally different from that found in the terrestrial sphere. The seventeenth century philosophers such as Galileo, Descartes and Newton maintained that celestial and terrestrial regions were made of similar kinds of material and subjected to the same natural laws.
The nineteenth century marked the astronomical research on majoring the positions and obtaining the motions of the astronomical objects this new astronomy began to emerge as astrophysics. William Hyde Wollaston and Joseph von Fraunhofer independently discovered that the light from the sun has many dark lines observed in its spectrum. Kirchhoff deduced that the dark lines in the solar spectrum are caused by absorption by chemical elements in the solar atmosphere. Harvard college observatory carried out a program of stellar spectral classification in 1885, the result was spectra recorded on photographic plates, by the end of nineteenth century a group of over ten thousand stars that grouped into 13 spectral types. By 1924 Harvard classification scheme was developed containing over a quarter of million stars the scheme was accepted by worldwide use. Around 1820 Edington speculated a source of stellar energy was fusion of hydrogen to helium liberating enormous energy according to Einstein’s energy equation.
Radio waves, X ray and gamma rays were a subject of study by the end of 20th century while gravitational waves are a concern in the 21st century.
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