Astrophysics
<p>Astronomy is one of the oldest sciences. Prehistoric cultures left behind astronomical artifacts such as the <a href="http://en.wikipedia.org/wiki/Egyptian_astronomy" title="Egyptian astronomy" >Egyptian monuments</a>, <a href="http://en.wikipedia.org/wiki/Nubian_pyramids" title="Nubian pyramids" >Nubian monuments</a> and <a href="http://en.wikipedia.org/wiki/Stonehenge" title="Stonehenge" >Stonehenge</a>, and early civilizations such as the <a href="http://en.wikipedia.org/wiki/Babylonian_astronomy" title="Babylonian astronomy" >Babylonians</a>, <a href="http://en.wikipedia.org/wiki/Greek_astronomy" title="Greek astronomy" >Greeks</a>, <a href="http://en.wikipedia.org/wiki/Chinese_astronomy" title="Chinese astronomy" >Chinese</a>, <a href="http://en.wikipedia.org/wiki/Indian_astronomy" title="Indian astronomy" >Indians</a>, <a href="http://en.wikipedia.org/wiki/Iranian_peoples" title="Iranian peoples" >Iranians</a> and <a href="http://en.wikipedia.org/wiki/Maya_civilization" title="Maya civilization" >Maya</a> performed methodical observations of the <a href="http://en.wikipedia.org/wiki/Night_sky" title="Night sky" >night sky</a>. However, the invention of the <a href="http://en.wikipedia.org/wiki/Telescope" title="Telescope" >telescope</a> was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as <a href="http://en.wikipedia.org/wiki/Astrometry" title="Astrometry" >astrometry</a>, <a href="http://en.wikipedia.org/wiki/Celestial_navigation" title="Celestial navigation" >celestial navigation</a>, observational astronomy, the making of<a href="http://en.wikipedia.org/wiki/Calendar" title="Calendar" >calendars</a>, and <a href="http://en.wikipedia.org/wiki/Astrology" title="Astrology" >astrology</a>, but professional astronomy is nowadays often considered to be synonymous with <a href="http://en.wikipedia.org/wiki/Astrophysics" title="Astrophysics" >astrophysics</a>.</p>
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<b >Astrophysics</b> (Greek: <i >Astro</i> - meaning "star", and Greek: <i >physis</i> – <i >φύσις</i> - meaning "nature") is the branch of <a href="http://en.wikipedia.org/wiki/Astronomy" title="Astronomy" >astronomy</a> that deals with the <a href="http://en.wikipedia.org/wiki/Physics" title="Physics" >physics</a> of the <a href="http://en.wikipedia.org/wiki/Universe" title="Universe" >universe</a>, including the physical properties of <a href="http://en.wikipedia.org/wiki/Astronomical_object" title="Astronomical object" >celestial objects</a>, as well as their interactions and behavior.<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Astrophysics#cite_note-0" >[1]</a></sup>
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Among the objects studied are <a href="http://en.wikipedia.org/wiki/Galaxy" title="Galaxy" >galaxies</a>, <a href="http://en.wikipedia.org/wiki/Star" title="Star" >stars</a>, <a href="http://en.wikipedia.org/wiki/Planet" title="Planet" >planets</a>, <a href="http://en.wikipedia.org/wiki/Exoplanet" title="Exoplanet" class="mw-redirect" >exoplanets</a>, the <a href="http://en.wikipedia.org/wiki/Interstellar_medium" title="Interstellar medium" >interstellar medium</a> and the <a href="http://en.wikipedia.org/wiki/Cosmic_microwave_background" title="Cosmic microwave background" class="mw-redirect" >cosmic microwave background</a>. Their emissions are examined across all parts of the <a href="http://en.wikipedia.org/wiki/Electromagnetic_spectrum" title="Electromagnetic spectrum" >electromagnetic spectrum</a>, and the properties examined include<a href="http://en.wikipedia.org/wiki/Luminosity" title="Luminosity" >luminosity</a>, <a href="http://en.wikipedia.org/wiki/Density" title="Density" >density</a>, <a href="http://en.wikipedia.org/wiki/Temperature" title="Temperature" >temperature</a>, and <a href="http://en.wikipedia.org/wiki/Chemistry" title="Chemistry" >chemical</a> composition. Because astrophysics is a very broad subject, <i >astrophysicists</i> typically apply many disciplines of physics, including<a href="http://en.wikipedia.org/wiki/Mechanics" title="Mechanics" >mechanics</a>, <a href="http://en.wikipedia.org/wiki/Electromagnetism" title="Electromagnetism" >electromagnetism</a>, <a href="http://en.wikipedia.org/wiki/Statistical_mechanics" title="Statistical mechanics" >statistical mechanics</a>, <a href="http://en.wikipedia.org/wiki/Thermodynamics" title="Thermodynamics" >thermodynamics</a>, <a href="http://en.wikipedia.org/wiki/Quantum_mechanics" title="Quantum mechanics" >quantum mechanics</a>, <a href="http://en.wikipedia.org/wiki/Theory_of_relativity" title="Theory of relativity" >relativity</a>, <a href="http://en.wikipedia.org/wiki/Nuclear_physics" title="Nuclear physics" >nuclear</a> and <a href="http://en.wikipedia.org/wiki/Particle_physics" title="Particle physics" >particle physics</a>, and <a href="http://en.wikipedia.org/wiki/Atomic,molecular,and_optical_physics" title="Atomic, molecular, and optical physics" >atomic and molecular physics</a>. In practice, modern astronomical research involves a substantial amount of physics. The name of a university's department ("astrophysics" or "astronomy") often has to do more with the department's history than with the contents of the programs. Astrophysics can be studied at the <a href="http://en.wikipedia.org/wiki/Bachelor%27s_degree" title="Bachelor's degree" >bachelors</a>, <a href="http://en.wikipedia.org/wiki/Master%27s_degree" title="Master's degree" >masters</a>, and <a href="http://en.wikipedia.org/wiki/Doctor_of_Philosophy" title="Doctor of Philosophy" >Ph.D.</a> levels in <a href="http://en.wikipedia.org/wiki/Aerospace_engineering" title="Aerospace engineering" >aerospace engineering</a>, physics, or astronomy departments at many <a href="http://en.wikipedia.org/wiki/University" title="University" >universities</a>.</p>