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[Portal] Astronomy

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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, 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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The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometers (864,000 miles), or 109 times that of Earth, and its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System. Roughly three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.

The Sun is a G-type main-sequence star (G2V) based on its spectral class. As such, it is informally and not completely accurately referred to as a yellow dwarf (its light is closer to white than yellow). It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is thought that almost all stars form by this process. Read more...

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A large sunspot group
Credit: NASA

Sunspots are temporary phenomena on the surface of the Sun (the photosphere) that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature. Although they are at temperatures of roughly 3,000–4,500 K (4,940–7,640 °F), the contrast with the surrounding material at about 5,780 K leaves them clearly visible as dark spots, as the intensity of a heated black body (closely approximated by the photosphere) is a function of T (temperature) to the fourth power.

Astronomy News

28 February 2020 –
A meteor explodes over Croatia. The Croatian Astronomical Union say the meteor disintegrated at an altitude of at least 30 kilometers above sea level. The meteor was likely roughly 2 meters across. (Xinhuanet) (The Dubrovnik Times) (JPL)
27 February 2020 –
Astronomers discover the largest known explosion ever in the history of the Universe, which occurred in the Ophiuchus galaxy cluster. It replaces MS 0735.6+7421. As space and ground telescopes that study radio emissions improve (which are better than X-ray observations for detecting these), more similar explosions, or "giant radio fossils", may be found. (Phys) (CNN) (Astrophysics via arXiv at Cornell University)
26 February 2020 –
Astronomers at the Catalina Sky Survey in Arizona, United States, say an object known as 2020 CD3 has been captured by Earth's gravitational field and has been in orbit since 2017, becoming a temporary natural satellite of Earth. The Minor Planet Center confirms the findings and says "no link to a known artificial object has been found", implying the object is an asteroid. (New Scientist)
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)

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All times UT unless otherwise specified.

8 March Neptune at conjunction
9 March, 17:48 Full moon
10 March, 06:36 Moon at perigee
18 March, 08:18 Moon occults Mars
18 March, 14:34 Moon occults Pluto
20 March, 03:50 Earth at northward equinox
24 March, 02:06 Mercury at greatest western elongation
24 March, 09:28 New moon
24 March, 15:40 Moon at apogee
24 March, 22:12 Venus at greatest eastern elongation

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This page was last updated at 2021-05-21 10:05, update this pageView original page

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