611 articles
Water on Mars
Water on Mars refers to water now on Mars, mostly ice, hydrated minerals, and vapor, plus strong evidence that rivers and lakes existed over 3 billion years ago.
Water vapor plumes on Europa
Water vapor plumes on Europa are putative eruptions of water vapor from Jupiter's moon Europa, first reported in 2012, whose existence a 2026 reanalysis called into question.
Wide-field Infrared Survey Explorer
The Wide-field Infrared Survey Explorer (WISE) was a NASA infrared space telescope launched in 2009 that mapped the entire sky, then hunted asteroids as NEOWISE until 2024.
Winter solstice
The winter solstice, also called midwinter's day, is when a hemisphere is tilted farthest from the Sun, giving the shortest day and least daylight of the year.
Wolf number
The Wolf number, also called the relative sunspot number, is a daily index of solar activity computed from sunspot counts, devised by Rudolf Wolf in 1848.
Yarkovsky effect
The Yarkovsky effect, also called the Yarkovsky force, is a tiny thermal recoil force on rotating, Sun-heated bodies such as asteroids that slowly shifts their orbits.
Year of the Solar System
The Year of the Solar System (YSS) was a NASA public engagement initiative from October 2010 to August 2012, celebrating an unprecedented rate of planetary missions.
Yondu
Yondu Udonta, usually called Yondu, is a Marvel Comics character: a blue-skinned archer from Alpha Centauri IV created by Arnold Drake and Gene Colan in 1969, a founding member of the original Guardians of the Galaxy.
YORP effect
The YORP effect (Yarkovsky–O'Keefe–Radzievskii–Paddack effect) is a torque from reflected and re-radiated sunlight that changes how fast irregularly shaped asteroids spin and how their spin axes point.
Zenithal hourly rate
The zenithal hourly rate (ZHR) is the standard measure of a meteor shower's activity, the number of meteors one observer would see per hour with the radiant at the zenith under ideal dark skies.
Zodiacal light
Zodiacal light, also called the zodiac band, is a faint cone of glow along the ecliptic caused by sunlight scattered off interplanetary dust, nicknamed the false dawn.