611 articles
Asteroid impact prediction
Asteroid impact prediction is the process of computing near-Earth object orbits and estimating collision probabilities with Earth, carried out continuously by NASA's Sentry and ESA's Aegis monitoring systems.
Asteroid mining
Asteroid mining is the proposed extraction of water, metals, and other materials from asteroids, targeted chiefly at water for rocket propellant; no commercial extraction has taken place yet.
Asteroid occultation
An asteroid occultation is the passage of an asteroid, centaur, or trans-Neptunian object in front of a distant star, briefly blocking its light as the shadow crosses Earth.
Asteroid spectral types
Asteroid spectral types are classes assigned from an asteroid's reflectance spectrum, whose shape indicates surface minerals; several taxonomies exist, with the Bus–DeMeo system of 25 classes most widely used.
Asteroid Terrestrial-impact Last Alert System
The Asteroid Terrestrial-impact Last Alert System (ATLAS) is a NASA-funded network of robotic telescopes in Hawaii, Chile, and South Africa that scans the sky nightly for incoming asteroids.
Astrological aspect
An astrological aspect, also called a planetary aspect, is an angle between two planets on the zodiac circle that astrologers read as meaningful, classified as harmonious or tense.
Astrological symbols
Astrological symbols, also called glyphs, are graphic signs for the Sun, Moon, planets, and zodiac signs, used in astrology and formerly in astronomy and now encoded in Unicode.
Astronomical chronology
Astronomical chronology, also known as astronomical dating, dates historical events by matching recorded eclipses with calculated positions of the Sun and Moon, fixing events like Babylon's fall in 539 BC.
Astronomical naming conventions
Astronomical naming conventions, or astronomical nomenclature, are the rules by which stars, planets, minor planets, and comets receive designations and proper names, standardized since 1919 by the International Astronomical Union.
Astronomical symbols
Astronomical symbols are graphic signs, such as ☿ for Mercury, representing the Sun, Moon, and planets in astronomy and astrology. The International Astronomical Union discourages their use in scientific publications.
Astronomy on Mars
Astronomy on Mars is the observation of celestial phenomena from the Martian surface, where the moons Phobos and Deimos cause frequent partial solar eclipses and rovers have photographed them since 2004.
Atmosphere of Io
The atmosphere of Io is the extremely thin, sulfur dioxide atmosphere of Jupiter's moon Io, supplied by volcanic outgassing and sublimating frost, collapsing nightly in Jupiter's shadow.
Atmosphere of Jupiter
The atmosphere of Jupiter (Jovian atmosphere) is an enormous envelope of hydrogen and helium with belts, zones, and the centuries-old Great Red Spot, twice as wide as Earth.
Atmosphere of Mars
The atmosphere of Mars, also called the Martian atmosphere, is a thin, carbon dioxide-dominated envelope of gas; its surface pressure is under one hundredth of Earth's sea-level pressure.
Atmosphere of Mercury
Mercury's atmosphere is a thin surface-bounded exosphere, the only planet without a substantial atmosphere, made of atoms blasted off its surface by solar wind and meteoroids.
Atmosphere of Neptune
Neptune's atmosphere, mostly hydrogen and helium with methane, is the most active of the giant planets, with winds up to 1,200 mph and storms like the Great Dark Spot.
Atmosphere of Pluto
The atmosphere of Pluto, also called Pluto's atmosphere, is a tenuous envelope of mostly nitrogen gas about 10 microbars in pressure, capped by a blue haze.
Atmosphere of Titan
The atmosphere of Titan is a dense envelope of nitrogen and methane surrounding Saturn's largest moon, the only moon in the solar system with a substantial atmosphere.
Atmosphere of Venus
The atmosphere of Venus is a dense carbon dioxide envelope with 92 bars of surface pressure and a 467 °C surface kept hot by a runaway greenhouse effect.
Atmospheric escape on Mars
Atmospheric escape on Mars is the ongoing loss of Martian atmosphere to space, driven by solar wind and photochemical processes; escape has removed at least 50% of the atmosphere.
Aurora
An aurora, also called polar lights or aurora borealis, is light in the upper atmosphere when charged particles from the magnetosphere excite atoms 100 to 400 km up.
Axial precession
Axial precession, also called the precession of the equinoxes, is the slow conical wobble of the Earth's rotation axis, completing a circle in about 26,000 years.
Axial tilt
Axial tilt, also called obliquity, is the angle between a planet's rotational axis and its orbital plane; Earth's tilt of about 23.5 degrees causes the seasons.
Ayló'chaxnim
Ayló'chaxnim is a red, roughly 2-kilometer asteroid, the first ever found orbiting entirely inside Venus's orbit, discovered by the Zwicky Transient Facility at Palomar Observatory on 2020 January 4.
Baily's beads
Baily's beads are bright pinpoints of sunlight that shine through valleys on the Moon's irregular edge in the seconds around totality during a solar eclipse.
Blue moon
A blue moon is an extra full moon, either the second in a calendar month or the third in a season of four; it rarely looks blue.
Bolide
A bolide is an exceptionally bright meteor, generally classified as a fireball; some definitions reserve the term for fireballs that explode or fragment in Earth's atmosphere.
Bond albedo
The Bond albedo, also called the spherical albedo, is the fraction of total incoming radiation, at all wavelengths and angles, that a body reflects back into space.
Bright spots on Ceres
The bright spots on Ceres are unusually reflective deposits, called faculae, made mostly of sodium carbonate left by evaporating salty brine, first seen by Hubble in 2004.
Budha (बुध)
Budha (बुध) is the Hindu planetary deity of Mercury in the Navagraha, son of the Moon and father of the lunar dynasty, ruling intellect and commerce.