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The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,265 astronomical units (AU), i.e. 30.9 trillion kilometres (19.2 trillion miles ). [a] The parsec unit is obtained by the use of parallax and trigonometry, and is ...
The Milky Way [c] is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.
The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy.
The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane parallel to an approximation of the galactic plane but offset to its north.
The first aspect of the Fermi paradox is a function of the scale or the large numbers involved: there are an estimated 200–400 billion stars in the Milky Way (2–4 × 10 11) and 70 sextillion (7×10 22) in the observable universe.
Stellar parallax is the apparent shift of position ( parallax) of any nearby star (or other object) against the background of distant stars. By extension, it is a method for determining the distance to the star through trigonometry, the stellar parallax method. Created by the different orbital positions of Earth, the extremely small observed ...
Highly luminous objects can have negative absolute magnitudes: for example, the Milky Way galaxy has an absolute B magnitude of about −20.8.
Milky Way: 1.6 × 10 42 kg: 2.4 × 10 15 m (0.25 ly) 5 × 10 20 m (52 900 ly) 0.000 029 kg/m 3: SMBH in Phoenix A (one of the largest known black holes) 2 × 10 41 kg: 3 × 10 14 m (~2000 AU) 0.0018 kg/m 3: Ton 618: 1.3 × 10 41 kg: 1.9 × 10 14 m (~1300 AU) 0.0045 kg/m 3: SMBH in NGC 4889: 4.2 × 10 40 kg: 6.2 × 10 13 m (~410 AU) 0.042 kg/m 3 ...
Usually the Sun (or Moon for nocturnal species) is the only light source and flying that way will result in a practically straight line. The arms of spiral galaxies. The Milky Way galaxy has several spiral arms, each of which is roughly a logarithmic spiral with pitch of about 12 degrees.
A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. [1] Several distinct components of a galaxy comprise its halo: [2] [3] the stellar halo. the galactic corona (hot gas, i.e. a plasma) the dark matter halo. The distinction between the halo and the main body of the galaxy is ...