Astronomy (from Ancient Greek ἀστρονομία (astronomía) 'science that studies the laws of the stars') 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 beyond Earth's atmosphere. Cosmology is a branch of astronomy that 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.

Astronomy is one of the few sciences in which amateurs play an active role. 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. ( Full article...)

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A stamp of Zhang Heng issued by China Post in 1955

Zhang Heng ( Chinese: 張 衡; AD 78–139), formerly romanized as Chang Heng, was a Chinese polymathic scientist and statesman who lived during the Han dynasty. Educated in the capital cities of Luoyang and Chang'an, he achieved success as an astronomer, mathematician, seismologist, hydraulic engineer, inventor, geographer, cartographer, ethnographer, artist, poet, philosopher, politician, and literary scholar.

Zhang Heng began his career as a minor civil servant in Nanyang. Eventually, he became Chief Astronomer, Prefect of the Majors for Official Carriages, and then Palace Attendant at the imperial court. His uncompromising stance on historical and calendrical issues led to his becoming a controversial figure, preventing him from rising to the status of Grand Historian. His political rivalry with the palace eunuchs during the reign of Emperor Shun (r. 125–144) led to his decision to retire from the central court to serve as an administrator of Hejian Kingdom in present-day Hebei. Zhang returned home to Nanyang for a short time, before being recalled to serve in the capital once more in 138. He died there a year later, in 139. ( Full article...)

• ... that the asteroid 2011 XC2 missed the Earth by less than 1 lunar distance on 3 December 2011?
• ... that the mass-luminosity relation, first derived by Arthur Eddington in 1924, helps astronomers find the distances to binary star systems?
• ... that the planetary nebula Abell 39 is unusually spherical, yet its central star is offset from the center?
• ... that data from Mariner 10 led to the discovery of Mercury's magnetic field in 1974?
• ... that the Toronto Magnetic Observatory had to be moved as the University of Toronto's electric lighting was interfering with observations?

• ... that The City in the Middle of the Night, a 2019 climate-fiction novel by Charlie Jane Anders, is set on a tidally locked planet?
• ... that fictional depictions of Jupiter have portrayed human habitation on the planet and its moons both by altering the environment to suit humans and altering humans to be suited to the environment?
• ... that pushbacks of migrants in the Aegean Sea have been described as "a human rights violation that encapsulates a will to eliminate a person's presence on the face of the planet"?
• ... that King Gizzard & the Lizard Wizard's " cli-fi" thrash metal album addresses a mix of current ecological threats and attempts to find another planet to live on?
• ... that by naming her album Planet Her, Doja Cat was "just trying to be cute" and was not promoting a feminist agenda nor a planet exclusively for women?
• ... that it took five years of observations to find the planet orbiting the star HD 175167?

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Credit: Yerkes Observatory

The 40-inch (1.02 m) refractor telescope backdrops Albert Einstein's visit to the Yerkes Observatory in May 1921. The 40-inch refractor telescope was modernized in the late 1960s with electronics of the period.

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• 7 March 2009 – The space observatory Kepler is launched by NASA to discover Earth-like planets orbiting other stars
• 13 March 1781 – William Herschel observes Uranus, which he initially believes to be a comet, eventually leading to Uranus being identified as a planet
• 14 March 1986 – The European robotic spacecraft Giotto becomes the first satellite to observe a comet up close when it flies through and photographs Halley's Comet
• 16 March 1926 – Using a mixture of gasoline and liquid oxygen, Robert H. Goddard launches the first liquid-fueled rocket
• 18 March 2011 – MESSENGER becomes the first spacecraft to orbit around the planet Mercury
• 23 March 1912 – Wernher von Braun, a German-American aerospace engineer and space architect is born