The Astronomy Portal
Astronomy (from Greek: ἀστρονομία) is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates outside Earth's atmosphere. Cosmology is a branch of astronomy. It studies the Universe as a whole.
Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Babylonians, Greeks, Indians, Egyptians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars. Nowadays, professional astronomy is often said to be the same as astrophysics.
Professional astronomy is split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results.
Amateurs play an active role in astronomy. It is one of the few sciences in which this is the case. This is especially true for the discovery and observation of transient events. Amateur astronomers have helped with many important discoveries, such as finding new comets.
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Image of Sirius
A and Sirius B taken by the Hubble Space Telescope
. Sirius B, which is a white dwarf, can be seen as a faint point of light to the lower left of the much brighter Sirius A.
A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. A white dwarf's faint luminosity comes from the emission of stored thermal energy; no fusion takes place in a white dwarf. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name white dwarf was coined by Willem Luyten in 1922.
White dwarfs are thought to be the final evolutionary state
of stars whose mass is not high enough to become a neutron star
, that of about 10 solar masses
. This includes over 97% of the other stars in the Milky Way
. After the hydrogen
period of a main-sequence star
of low or medium mass ends, such a star will expand to a red giant
during which it fuses helium
in its core by the triple-alpha process
. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon (around 1 billion K), an inert mass of carbon and oxygen will build up at its center. After such a star sheds its outer layers and forms a planetary nebula
, it will leave behind a core, which is the remnant white dwarf. Usually, white dwarfs are composed of carbon and oxygen. If the mass of the progenitor is between 8 and 10.5 solar masses
), the core temperature will be sufficient to fuse carbon but not neon
, in which case an oxygen–neon–magnesium
white dwarf may form. Stars of very low mass will not be able to fuse helium, hence, a helium white dwarf may form by mass loss in binary systems. Read more...
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- 20 April 2020 –
- New data from the Atacama Large Millimeter Array and Hubble Space Telescope, published in the Nature Astronomy journal, suggests interstellar comet 2I/Borisov contains large amounts of carbon monoxide and hydrogen cyanide. The new findings suggest the object was formed in the cold outer region of its planetary system. (BBC)
- 7 April 2020 –
- Astronomers report, via The Astronomer's Telegram, that comet C/2019 Y4 (ATLAS) appears to have disintegrated. (The Independent)
- 13 March 2020 – Planets beyond Neptune
- Astronomers discover 139 new "minor planets" in the Solar System that are beyond the orbit of Neptune, which helps boost odds of finding Planet Nine. (NBC News)
- 28 February 2020 –
- A meteor explodes over Croatia. The Croatian Astronomical Union say the meteor disintegrated at an altitude of at least 30 kilometers above sea level. The meteor was likely roughly 2 meters across. (Xinhuanet) (The Dubrovnik Times) (JPL)
- 27 February 2020 –
- Astronomers discover the largest known explosion ever in the history of the Universe, which occurred in the Ophiuchus galaxy cluster. It replaces MS 0735.6+7421. As space and ground telescopes that study radio emissions improve (which are better than X-ray observations for detecting these), more similar explosions, or "giant radio fossils", may be found. (Phys) (CNN) (Astrophysics via arXiv at Cornell University)
- 26 February 2020 –
- Astronomers at the Catalina Sky Survey in Arizona, United States, say an object known as 2020 CD3 has been captured by Earth's gravitational field and has been in orbit since 2017, becoming a temporary natural satellite of Earth. The Minor Planet Center confirms the findings and says "no link to a known artificial object has been found", implying the object is an asteroid. (New Scientist)
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