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A man sitting on a chair mounted to a moving platform, staring through a large telescope.
Percival Lowell observing Venus from the Lowell Observatory telescope in 1914

Astronomy 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, meteoroid, asteroid, 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...)

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View of trailing hemisphere in natural color

Enceladus is the sixth-largest moon of Saturn (19th largest in the Solar System). It is about 500 kilometers (310 miles) in diameter, about a tenth of that of Saturn's largest moon, Titan. It is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only −198 °C (75.1 K; −324.4 °F), far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide range of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrain.

Enceladus was discovered on August 28, 1789 by William Herschel, but little was known about it until the two Voyager spacecraft, Voyager 1 and Voyager 2, flew by Saturn in 1980 and 1981. In 2005, the spacecraft Cassini started multiple close flybys of Enceladus, revealing its surface and environment in greater detail. In particular, Cassini discovered water-rich plumes venting from the south polar region. Cryovolcanoes near the south pole shoot geyser-like jets of water vapor, molecular hydrogen, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totaling about 200 kilograms (440 pounds) per second. More than 100 geysers have been identified. Some of the water vapor falls back as "snow"; the rest escapes and supplies most of the material making up Saturn's E ring. According to NASA scientists, the plumes are similar in composition to comets. In 2014, NASA reported that Cassini had found evidence for a large south polar subsurface ocean of liquid water with a thickness of around 10 km (6 mi). The existence of Enceladus' subsurface ocean has since been mathematically modelled and replicated. (Full article...)

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Credit: NASA

Geodynamics of Venus as seen from a global radar view of the surface from Magellan probe radar imaging between 1990 and 1994. The age of Venus was revealed by the observation of over 900 impact craters on the surface of the planet.

Astronomy News

14 June 2023 –
Astronomers report that the presence of phosphates on Enceladus, moon of the planet Saturn, has been detected, completing the discovery of all the basic chemical ingredients for life on the moon. (New York Times)
12 June 2023 – Discoveries of exoplanets
Astronomers announce in the journal Nature Astronomy the discovery of BEBOP-1c, an exoplanet orbiting the binary star system, TOI-1338. The system is the second discovered to have more than one circumbinary planet. (Space.com)
5 April 2023 – Discoveries of exoplanets
Scientists discover bursts of radiation in radio wavelengths on the exoplanet YZ Ceti b, which is part of the YZ Ceti system. The studies are published in the Nature Astronomy journal. (The Jerusalem Post)

September anniversaries

Space-related Portals

Astronomical events

All times UT unless otherwise specified.

6 September, 11:03 Mercury at inferior conjunction
12 September, 15:42 Moon at apogee
15 September, 01:40 New moon
19 September, 09:54 Neptune at opposition
22 September, 12:59 Mercury at greatest western elongation
23 September, 06:50 Earth southward equinox
28 September, 01:05 Moon at perigee
29 September, 09:57 Full moon



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