The Astronomy Portal

Introduction

A man sitting on a chair mounted to a moving platform, staring through a large telescope.

Astronomy (from Greek: ἀστρονομία) 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 outside Earth's atmosphere. Cosmology is a branch of astronomy. It 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, Nubians, Iranians, 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.

Amateurs play an active role in astronomy. It is one of the few sciences in which this is the case. 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.

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Triton moon mosaic Voyager 2 (large).jpg

Triton is the largest natural satellite of the planet Neptune, and the first Neptunian moon to be discovered. The discovery was made on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the direction opposite to its planet's rotation. At 2,710 kilometres (1,680 mi) in diameter, it is the seventh-largest moon in the Solar System, the only satellite of Neptune massive enough to be in hydrostatic equilibrium and the second-largest planetary moon in relation to its primary, after Earth's Moon. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been a dwarf planet captured from the Kuiper belt.

Triton has a surface of mostly frozen nitrogen, a mostly water-ice crust, an icy mantle and a substantial core of rock and metal. The core makes up two-thirds of its total mass. The mean density is 2.061 g/cm3, reflecting a composition of approximately 15–35% water ice. Read more...

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Mimas Cassini.jpg
Credit: NASA / JPL-Caltech / Space Science Institute

Mimas is a moon of Saturn. It was discovered in 1789 by William Herschel, after whom the large crater in the image is named. It is the twentieth-largest moon in the Solar System, and the smallest astronomical body that is known to be rounded in shape because of self-gravitation. This photograph of Mimas was taken by the unmanned spacecraft Cassini in 2010.

Astronomy News

7 October 2019 –
Astronomers announce the discovery of 20 new moons around Saturn, adding to the 62 previously known. The new moons comprise 17 retrograde moons in the Norse group and three prograde moons, two of which belong to the Inuit group. (Phys.org)
12 September 2019 – Interstellar objects
C/2019 Q4 (Borisov), a second interstellar comet after ʻOumuamua in 2017, is discovered by an amateur astronomer. (BBC)
19 August 2019 –
Astronomers led by a team from McGill University in Montreal announce the detection of eight new repeating fast radio bursts (FRBs) using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope. The astronomers report they also found complex morphologies and downward-drifting sub-bursts in some of the eight new FRBs. (Phys.org)
1 August 2019 – List of nearest exoplanets
Astronomers from the Max Planck Institute for Astronomy announce the discovery of red dwarf star GJ 357 and its three confirmed exoplanets in the Hydra constellation, one of which (GJ 357 d) is highly likely to be a super-Earth planet located in the system's circumstellar habitable zone where life can exist. The discovery was made using NASA's Transiting Exoplanet Survey Satellite (TESS). (The Independent)
17 July 2019 –
Astronomers rule out the chances of ~30-meter asteroid 2006 QV89's impacting Earth in September 2019 by eliminating the possibility of its passing through an area where it would have to be if it were on an impacting orbit. Prior to this, the asteroid had been given a one-in-7,000 chance of impacting Earth. (phys.org)
31 January 2019 –
Astronomers announce, through the Monthly Notices of the Royal Astronomical Society journal, the accidental discovery of dwarf spheroidal galaxy Bedin I in the Pavo constellation in September 2018. (Space Telescope)

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Astronomical events

All times UT unless otherwise specified.

2 January, 01:32 Moon at apogee
4 January, 09:00 Quadrantids peak
5 January, 07:48 Earth at perihelion
10 January, 15:18 Mercury at superior conjunction
10 January, 19:21 Full moon and penumbral lunar eclipse
13 January Pluto at conjunction
13 January, 15:00 Saturn at conjunction, occultation
13 January, 20:29 Moon at perigee
23 January, 02:41 Moon occults Jupiter
24 January, 00:06 Moon occults Pluto
24 January, 21:42 New moon
29 January, 21:33 Moon at apogee

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