Milky Way

galaxyMilky Way Galaxyour galaxy
Maps of artificial night sky brightness show that more than one-third of Earth's population cannot see the Milky Way from their homes due to light pollution. As viewed from Earth, the visible region of the Milky Way's galactic plane occupies an area of the sky that includes 30 constellations. The Galactic Center lies in the direction of Sagittarius, where the Milky Way is brightest. From Sagittarius, the hazy band of white light appears to pass around to the galactic anticenter in Auriga. The band then continues the rest of the way around the sky, back to Sagittarius, dividing the sky into two roughly equal hemispheres.

Astronomical object

celestial bodiescelestial bodycelestial object
Depending on the initial mass of the star and the presence or absence of a companion, a star may spend the last part of its life as a compact object; either a white dwarf, neutron star, or black hole. The table below lists the general categories of bodies and objects by their location or structure. * Monthly skymaps for every location on Earth List of light sources. List of Solar System objects. Lists of astronomical objects.

Alpha Centauri

α CentauriAlphaα Centauri A
Tolimân is Golius' latinisation of the Arabic name الظلمان al-Ẓulmān "the ostriches", the name of an asterism of which Alpha Centauri formed the main star. During the 19th century, the northern amateur popularist Elijah H. Burritt used the now-obscure name Bungula, possibly coined from "β" and the Latin ungula ("hoof"). Together, Alpha and Beta Centauri form the "Southern Pointers" or "The Pointers", as they point towards the Southern Cross, the asterism of the constellation of Crux. In Standard Mandarin Chinese, 南門 Nán Mén, meaning Southern Gate, refers to an asterism consisting of α Centauri and ε Centauri.


Lat.Latin languagelat
Several states of the United States have Latin mottos: such as Connecticut's motto Qui transtulit sustinet ("He who transplanted sustains"); Kansas's Ad astra per aspera ("To the stars through hardships"); Michigan's Si quaeris peninsulam amoenam, circumspice ("If you seek a pleasant peninsula, look about you"); Missouri's Salus populi suprema lex esto ("The health of the people should be the highest law"); North Carolina's Esse quam videri ("To be rather than to seem"); Virginia's Sic semper tyrannis ("Thus always to tyrants"); and West Virginia's Montani semper liberi ("Mountaineers are always free").


luminousbolometric luminosityluminosities
Some such as the UBV or Johnson system are defined against photometric standard stars, while others such as the AB system are defined in terms of a spectral flux density. A star's luminosity can be determined from two stellar characteristics: size and effective temperature. The former is typically represented in terms of solar radii, R ⊙, while the latter is represented in kelvins, but in most cases neither can be measured directly. To determine a star's radius, two other metrics are needed: the star's angular diameter and its distance from Earth, often calculated using parallax.

Open cluster

open star clusterstar clusteropen clusters
When a Hertzsprung-Russell diagram is plotted for an open cluster, most stars lie on the main sequence. The most massive stars have begun to evolve away from the main sequence and are becoming red giants; the position of the turn-off from the main sequence can be used to estimate the age of the cluster. Because the stars in an open cluster are all at roughly the same distance from Earth, and were born at roughly the same time from the same raw material, the differences in apparent brightness among cluster members is due only to their mass.

Star catalogue

star catalogNLTTLTT
For his Spiritual Constitution of the Universe (靈憲, Ling Xian) of 120 AD, the astronomer Zhang Heng (78–139 AD) compiled a star catalogue comprising 124 constellations. Chinese constellation names were later adopted by the Koreans and Japanese. A large number of star catalogues were published by Muslim astronomers in the medieval Islamic world. These were mainly Zij treatises, including Arzachel's Tables of Toledo (1087), the Maragheh observatory's Zij-i Ilkhani (1272) and Ulugh Beg's Zij-i-Sultani (1437).

SN 1054

supernova of 10541054 Supernovaa 3-week long supernova in 1054
The asterisms (or "constellations") of Chinese astronomy were catalogued around the 2nd century BC. The asterisms with the brightest stars in the sky were compiled in a work called Shi Shi, which also includes Tianguan. Identification of Tianguan is comparatively easy, as it is indicated that it is located at the foot of the Five Chariots asterism, the nature of which is left in hardly any doubt by representation on maps of the Chinese sky: it consists of a large pentagon containing the bright stars of the Auriga.

Zeta Ophiuchi

ζ Ophiuchiζ Oph*zet Oph
Zeta Ophiuchi (ζ Oph, ζ Ophiuchi) is a star located in the constellation of Ophiuchus. It has an apparent visual magnitude of 2.57, making it the third-brightest star in the constellation. Parallax measurements give an estimated distance of roughly 366 ly from the Earth. ζ Ophiuchi is an enormous star with more than 19 times the Sun's mass and eight times its radius. The stellar classification of this star is O9.5 V, with the luminosity class of V indicating that it is generating energy in its core by the nuclear fusion of hydrogen. This energy is being emitted from the outer envelope at an effective temperature of 34,000K, giving the star the blue hue of an O-type star.

Outline of astronomy

Variable star. Star systems. Binary star. Contact binary. Common envelope. Multiple star. Accretion disc. Planetary system. Earth's Solar System. Earth-centric observation of stars. Pole star. Circumpolar star. Magnitude. Apparent magnitude. Photographic magnitude. color-color diagram. Radial velocity. Proper motion. Parallax#Stellar parallax. Photometric-standard star. Lists of stars. List of proper names of stars. List of Arabic star names. Traditional Chinese star names. List of most massive stars. List of least massive stars. List of largest known stars. List of brightest stars. Historical brightest stars. List of most luminous stars. List of nearest stars. List of nearest bright stars.

The Great Dipper (album)

The Great Dipper
I began writing the song after being impressed by the fact that we get to see the asterism wherever on Earth stars are visible. (However,) it was actually the Orion's Belt rather than the Big Dipper." He added that "Not only exactly for romance or love, I hope the song becomes a direction for those who are pinched with cold, worried, or disoriented." "The Great Dipper" peaked at number 30 on the Gaon Digital Chart, having sold nearly 308,000 digital copies domestically as of the first half of 2016. On December 3, 2015, a day prior to the album's release, Kim held a comeback showcase at Understage, Yongsan-gu in Seoul.

Cosmic dust

interstellar dustdustspace dust
Thousands of tons of cosmic dust are estimated to reach the Earth's surface every year, with each grain having a mass between 10 −16 kg (0.1 pg) and 10 −4 kg (100 mg). The density of the dust cloud through which the Earth is traveling is approximately 10 −6 /m 3. Cosmic dust contains some complex organic compounds (amorphous organic solids with a mixed aromatic–aliphatic structure) that could be created naturally, and rapidly, by stars. A smaller fraction of dust in space is "stardust" consisting of larger refractory minerals that condensed as matter left by stars. Interstellar dust particles were collected by the Stardust spacecraft and samples were returned to Earth in 2006.


solarSolThe Sun
The Apex of the Sun's Way, or the solar apex, is the direction that the Sun travels relative to other nearby stars. This motion is towards a point in the constellation Hercules, near the star Vega. Of the 50 nearest stellar systems within 17 light-years from Earth (the closest being the red dwarf Proxima Centauri at approximately 4.2 light-years), the Sun ranks fourth in mass. The Sun orbits the center of the Milky Way, and it is presently moving in the direction of the constellation of Cygnus.


planetsFormer classification of planetsplanetary-mass object
Terrestrials: Planets that are similar to Earth, with bodies largely composed of rock: Mercury, Venus, Earth and Mars. At 0.055 Earth masses, Mercury is the smallest terrestrial planet (and smallest planet) in the Solar System. Earth is the largest terrestrial planet. Giant planets (Jovians): Massive planets significantly more massive than the terrestrials: Jupiter, Saturn, Uranus, Neptune. Gas giants, Jupiter and Saturn, are giant planets primarily composed of hydrogen and helium and are the most massive planets in the Solar System. Jupiter, at 318 Earth masses, is the largest planet in the Solar System, and Saturn is one third as massive, at 95 Earth masses.


lunarthe MoonLuna
If the Earth were a water world (one with no continents) it would produce a tide of only one meter, and that tide would be very predictable, but the ocean tides are greatly modified by other effects: the frictional coupling of water to Earth's rotation through the ocean floors, the inertia of water's movement, ocean basins that grow shallower near land, the sloshing of water between different ocean basins. As a result, the timing of the tides at most points on the Earth is a product of observations that are explained, incidentally, by theory.


livinglife on Earthbiota
Beyond the Solar System, the region around another main-sequence star that could support Earth-like life on an Earth-like planet is known as the habitable zone. The inner and outer radii of this zone vary with the luminosity of the star, as does the time interval during which the zone survives. Stars more massive than the Sun have a larger habitable zone, but remain on the Sun-like "main sequence" of stellar evolution for a shorter time interval. Small red dwarfs have the opposite problem, with a smaller habitable zone that is subject to higher levels of magnetic activity and the effects of tidal locking from close orbits.

Stellar evolution

A star with an initial mass above about will be able to reach temperatures high enough to fuse helium, and these "mid-sized" stars go on to further stages of evolution beyond the red giant branch. Stars of roughly become red giants, which are large non-main-sequence stars of stellar classification K or M. Red giants lie along the right edge of the Hertzsprung–Russell diagram due to their red color and large luminosity. Examples include Aldebaran in the constellation Taurus and Arcturus in the constellation of Boötes.