The Astronomy Portal


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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Known objects in the Kuiper belt beyond the orbit of Neptune. (Scale in AU; epoch as of January 2015.)
  Jupiter trojans
  Giant planets:
  Neptune trojans
  Resonant Kuiper belt
  Classical Kuiper belt
  Scattered disc
Distances but not sizes are to scale. The yellow disk is about the size of Mars' orbit.
Source: Minor Planet Center, and others

The Kuiper belt (/ˈkpər/ KY-pər) is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times as wide and 20–200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed. While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia, and water. The Kuiper belt is home to most of the objects that astronomers generally accept as dwarf planets: Orcus, Pluto, Haumea, Quaoar, and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, may have originated in the region.

The Kuiper belt is named in honor of Dutch astronomer Gerard Kuiper, who conjectured the existence of a similar belt in 1951. However, it was not until 1980 that astronomer Julio Angel Fernandez published a paper suggesting the existence of a comet belt beyond Neptune, which could serve as a source for short-period comets. Although the Kuiper belt is named after Gerard Kuiper, Fernandez was the researcher who first predicted its existence. (Full article...)

More Did you know (auto generated)

  • ... that Mariner 1, the United States' first interplanetary probe, was lost in 1962 due to the miscoding of a single character in its software?
  • ... 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 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 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 Nandivada Rathnasree, who ran Delhi's planetarium, proposed that astronomers could be taught using India's stone-built observatories?
  • ... that it took five years of observations to find the planet orbiting the star HD 175167?


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Credit: Nathan Smith (University of California, Berkeley) / NASA

Gamma-ray burst progenitors are the types of celestial objects that can emit gamma-ray bursts (GRBs). GRBs show an extraordinary degree of diversity. They can last anywhere from a fraction of a second to many minutes. Image is Eta Carinae, in the constellation of Carina, one of the nearer candidates for a hypernova.

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. (
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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