Portal:Astronomy

Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, 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 Egyptians, Babylonians, Greeks, Indians, 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.

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...)

In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of stars on and off the band are believed to indicate their physical properties, as well as their progress through several types of star life-cycles. These are the most numerous true stars in the universe and include the Sun. Color-magnitude plots are known as Hertzsprung–Russell diagrams after Ejnar Hertzsprung and Henry Norris Russell.

After condensation and ignition of a star, it generates thermal energy in its dense core region through nuclear fusion of hydrogen into helium. During this stage of the star's lifetime, it is located on the main sequence at a position determined primarily by its mass but also based on its chemical composition and age. The cores of main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. The strong dependence of the rate of energy generation on temperature and pressure helps to sustain this balance. Energy generated at the core makes its way to the surface and is radiated away at the photosphere. The energy is carried by either radiation or convection, with the latter occurring in regions with steeper temperature gradients, higher opacity, or both. (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 a profile of artist Mark Hearld said his "wrens and squirrels, field mice and owls" help a child care about the planet better than telling them it is burning?
• ... that the active galaxy 3C 120 was given the variable-star designation BW Tauri because of its variability in the visible spectrum?
• ... that one night on the planet Venus lasts just over 58 full days on Earth?
• ... 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 the Springfield Science Museum is home to the oldest operating projection planetarium in the United States?
• ... that in many works of fiction, the asteroid belt is the remnants of a destroyed planet?

Luminous blue variables (LBVs) are massive evolved stars that show unpredictable and sometimes dramatic variations in both their spectra and brightness. Luminous blue variable AG Carinae in the constellation Carina as seen by the Hubble Space Telescope.

23 June 2025 –

The Vera C. Rubin Observatory in Chile releases the first light images from its new 8.4-meter (28 ft) telescope. (Scientific American)

• 4 August 2007 – The Phoenix Mars Lander is launched from Cape Canaveral, carrying science instruments to analyze soil samples of the Martian northern polar region
• 6 August 2012 – The Mars rover Curiosity lands on the Red Planet as part of NASA's Mars Science Laboratory mission
• 7 August 1996 – Announcement of possible microfossils found in ALH84001 Martian Meteorite
• 20 August 1977 – Voyager 2 space probe is launched by NASA to study the outer planets and interstellar space beyond the Sun's heliosphere
• 21 August 2017 – NASA.gov conducts a broadcast of the total solar eclipse with more than 50 million views of the live broadcast, and almost 31 million unique views on Facebook before and after the eclipse
• 24 August 2006 – The International Astronomical Union votes to approve a new definition of "planet" that excludes Pluto
• 25 August 2003 – The Spitzer Space Telescope (SIRTF) is launched, dedicated to infrared astronomy
• 27 August 1962 – Mariner 2 launches on a journey to Venus, and is the first robotic space probe to conduct a successful planetary encounter
• 31 August 1913 – Bernard Lovell, a British physicist and radio astronomer is born