Astrophysics

Astrophysics is the study of how stars, planets, and other things in the Universe work, and how we can learn about them. Astrophysicists use physics and chemistry to explain what astronomers find and see.Keeler, James E. 1897. The importance of astrophysical research and the relation of astrophysics to the other physical sciences. The Astrophysical Journal, 6 (4): 271–288, Bibcode:1897ApJ.....6..271K, doi:10.1086/140401, PMID 17796068

Astrophysics is also the study of how the Universe started and how it is changing with time. This part of astrophysics is called cosmology.

 History 

For a long time, bodies in the sky seemed to be unchanging spheres moving in a circle. But on Earth, growth and decay happened, and natural motion was in a straight line. Therefore, people thought the celestial region was made of a fundamentally different kind of matter from that found on Earth.

During the 16th and 17th centuries, natural philosophers such as Nicolaus Copernicus, Johannes Kepler, Galileo, Descartes, and Newton, began to maintain that the celestial and terrestrial regions were made of similar material and were subject to the same natural laws.Burtt, Edwin Arthur [1924] 2003. The metaphysical foundations of modern science . 2nd ed, Mineola, NY: Dover, pp. 30, 41, 241–2. 

When they were able to work out how the planets moved, the science of astrophysics was born. Sir Isaac Newton realized that the same rules of mechanics that he had found on the surface of the Earth also could be used to predict how the planets moved. He said, "As above, so below". By this, he meant that we can study how things work on this planet to find out how things work in space.

Later scientists looked at the light from stars using spectroscopy.  They were able to work out what they were made of, and how they changed with time.

 Types of astrophysics 

There are two main types of astrophysics:

Observational astrophysics. Observational astrophysicists use telescopes to study the Universe, but astrophysicists study the physics of what they see to explain the Universe.
Radio astronomy
Optical astronomy
Infrared astronomy
Ultraviolet, X-ray, and gamma-ray astronomy using space telescopes
Theoretical astrophysics uses information from astronomers, theories, and mathematics to explain how the Universe works. Cosmology is a type of theoretical astrophysics. Problems investigated include: 
Solar System: its formation and evolution
Star formation and evolution
Galaxy formation and evolution
large-scale structure of matter in the universe 
Origin of cosmic rays 
General relativity 
Evolution of the universe
Hydrodynamics is used for mathematically modelling how gases behave. Strong magnetic fields found around many bodies can drastically change how these gases behave, affecting things from star formation to the flows of gases around compact stars. 

 An example 
Cecilia Helena Payne (later Cecilia Payne-Gaposchkin) published her doctoral dissertation at Radcliffe College in 1925. She had discovered that hydrogen and helium were the main content of stars. More than that, the spectral classes relate to the temperature of stars. Despite Eddington's suggestion,Eddington correctly speculated that the source was fusion of hydrogen into helium, which gave off enormous energy according to Einstein's equation E = mc2. her discovery was so unexpected that her dissertation readers told her to modify the conclusion before publication. Later research confirmed her discovery.Payne C.H. 1925. Stellar Atmospheres; a contribution to the observational Study of high temperature in the reversing layers of stars (PhD Thesis), Cambridge, Massachusetts: Radcliffe College.Haramundanis, Katherine 2007. "Payne-Gaposchkin [Payne], Cecilia Helena", in Hockey, Thomas; Trimble, Virginia; Williams, Thomas R. (eds), Biographical Encyclopedia of Astronomers, New York: Springer, pp. 876–878, ISBN 978-0-387-30400-7, retrieved July 19, 2015

Related pages
 Astronomy
 Celestial mechanics
 Quasar

 References