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Underlined terms are entries in the glossary - double click to highlight and ctrl+f.

General Glossary

Term Definition
Space How space should be defined is debated but informally it is a spatial complex defined for the three familar linear dimensions and the medium that all astronomical bodies sit in.
Barycenter The center of mass formed by two or more objects orbiting around each other. From Ancient Greek barús (heavy) and kéntron (center).
Central Massive Object (CMO) The high-mass object or cluster of objects at the center of a body such as a galaxy or globular cluster.
Exoplanet / Extrasolar Planet A planet outside the Solar System.


Specific Astronomical Objects

Object Information
Milky Way Galaxy The galaxy that includes the Solar System.
  • The name comes from its appearance from Earth as a hazy wash of light formed from many stars that cannot be individually distinguished by the naked human eye.
  • It is estimated to have 100-400 billion stars and at least that many planets.
Galatic Center The barycenter of the Milky Way and a point on the rotational axis of the galaxy. Its CMO is the supermassive black hole Sagittarius A*.
Sagittarius A* The supermassive black hole at the Galatic Center of the Milky Way galaxy. Its mass is 4.297±0.012 million solar masses.


Units

Unit Value
Solar Mass Approximately 2 * 1030 kg or the mass of the Sun.
  • Approx. 333,000 times the mass of the Earth.
Astronomical Unit [au] 149,597,870,700 meters. Before this modern definition was adopted in 2012 it was concieved as the average distance between the Sun and the Earth.
  • Approx. 499 light-seconds.
Parsec [pc] Appox. 3.26 light-years or 206,265 AU. It is defined as the distance at which 1 AU subtends an angle of 1/3600 of a degree.
Light-year / Light Year [ly] 9,460,730,472,580.8 km. It is defined as the distance light travels in a vacuum in 365.25 days.