Astronomy

The Paranal Observatory of European Southern Observatory is shooting a laser guide star to the Galactic Center
Astronomical Observatory, New South Wales, Australia 1873
19th-century Quito Astronomical Observatory is located 12 minutes south of the Equator in Quito, Ecuador.
A celestial map from the 17th century, by the Dutch cartographer Frederik de Wit
The Suryaprajnaptisūtra, a 6th-century BC astronomy text of Jains at The Schoyen Collection, London. Above: its manuscript from c. 1500 AD.
Greek equatorial sundial, Alexandria on the Oxus, present-day Afghanistan 3rd–2nd century BC
Galileo's sketches and observations of the Moon revealed that the surface was mountainous.
An astronomical chart from an early scientific manuscript, c. 1000
The Very Large Array in New Mexico, an example of a radio telescope
ALMA Observatory is one of the highest observatory sites on Earth. Atacama, Chile.
The Subaru Telescope (left) and Keck Observatory (center) on Mauna Kea, both examples of an observatory that operates at near-infrared and visible wavelengths. The NASA Infrared Telescope Facility (right) is an example of a telescope that operates only at near-infrared wavelengths.
X-ray jet made from a supermassive black hole found by NASA's Chandra X-ray Observatory, made visible by light from the early Universe
Star cluster Pismis 24 with a nebula
Astrophysics applies physics and chemistry to understand the measurements made by astronomy. Representation of the Observable Universe that includes images from Hubble and other telescopes.
Hubble Extreme Deep Field
This image shows several blue, loop-shaped objects that are multiple images of the same galaxy, duplicated by the gravitational lens effect of the cluster of yellow galaxies near the middle of the photograph. The lens is produced by the cluster's gravitational field that bends light to magnify and distort the image of a more distant object.
Observed structure of the Milky Way's spiral arms
Mz 3, often referred to as the Ant planetary nebula. Ejecting gas from the dying central star shows symmetrical patterns unlike the chaotic patterns of ordinary explosions.
An ultraviolet image of the Sun's active photosphere as viewed by the TRACE space telescope. NASA photo
Solar observatory Lomnický štít (Slovakia) built in 1962
The black spot at the top is a dust devil climbing a crater wall on Mars. This moving, swirling column of Martian atmosphere (comparable to a terrestrial tornado) created the long, dark streak.
Amateur astronomers can build their own equipment, and hold star parties and gatherings, such as Stellafane.

Natural science that studies celestial objects and phenomena.

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Cosmology

Branch of metaphysics dealing with the nature of the universe.

The Hubble eXtreme Deep Field (XDF) was completed in September 2012 and shows the farthest galaxies ever photographed. Except for the few stars in the foreground (which are bright and easily recognizable because only they have diffraction spikes), every speck of light in the photo is an individual galaxy, some of them as old as 13.2 billion years; the observable universe is estimated to contain more than 2 trillion galaxies.
Representation of the observable universe on a logarithmic scale.

In the science of astronomy it is concerned with the study of the chronology of the universe.

Astrometry

Illustration of the use of interferometry in the optical wavelength range to determine precise positions of stars. Courtesy NASA/JPL-Caltech
Concept art for the TAU spacecraft, a 1980s era study which would have used an interstellar precursor probe to expand the baseline for calculating stellar parallax in support of Astrometry
Diagram showing how a smaller object (such as an extrasolar planet) orbiting a larger object (such as a star) could produce changes in position and velocity of the latter as they orbit their common center of mass (red cross).
Motion of barycenter of solar system relative to the Sun.

Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies.

Astronomical object

Naturally occurring physical entity, association, or structure that exists in the observable universe.

Composite image showing the round dwarf planet Ceres; the slightly smaller, mostly round Vesta; and the much smaller, much lumpier Eros

In astronomy, the terms object and body are often used interchangeably.

Indian astronomy

A page from the Hindu calendar 1871–72.
Jantar Mantar (Jaipur) observatory.
Yantra Mandir (completed by 1743 CE), Delhi.
Astronomical instrument with graduated scale and notation in Hindu-Arabic numerals.
Detail of an instrument in the Jaipur observatory.
Greek equatorial sun dial, Ai-Khanoum, Afghanistan 3rd–2nd century BCE.
Division of hours, minutes and seconds

Astronomy has long history in Indian subcontinent stretching from pre-historic to modern times.

Chemistry

Scientific study of the properties and behavior of matter.

An oil painting of a chemist (Ana Kansky, painted by Henrika Šantel in 1932)
Laboratory, Institute of Biochemistry, University of Cologne in Germany.
Solutions of substances in reagent bottles, including ammonium hydroxide and nitric acid, illuminated in different colors
A diagram of an atom based on the Bohr model
Standard form of the periodic table of chemical elements. The colors represent different categories of elements
Carbon dioxide (CO2), an example of a chemical compound
A ball-and-stick representation of the caffeine molecule (C8H10N4O2).
A 2-D structural formula of a benzene molecule (C6H6)
Diagram showing relationships among the phases and the terms used to describe phase changes.
An animation of the process of ionic bonding between sodium (Na) and chlorine (Cl) to form sodium chloride, or common table salt. Ionic bonding involves one atom taking valence electrons from another (as opposed to sharing, which occurs in covalent bonding)
In the methane molecule (CH4), the carbon atom shares a pair of valence electrons with each of the four hydrogen atoms. Thus, the octet rule is satisfied for C-atom (it has eight electrons in its valence shell) and the duet rule is satisfied for the H-atoms (they have two electrons in their valence shells).
Emission spectrum of iron
During chemical reactions, bonds between atoms break and form, resulting in different substances with different properties. In a blast furnace, iron oxide, a compound, reacts with carbon monoxide to form iron, one of the chemical elements, and carbon dioxide.
The crystal lattice structure of potassium chloride (KCl), a salt which is formed due to the attraction of K+ cations and Cl− anions. Note how the overall charge of the ionic compound is zero.
Hydrogen bromide exists in the gas phase as a diatomic molecule
Democritus' atomist philosophy was later adopted by Epicurus (341–270 BCE).
15th-century artistic impression of Jābir ibn Hayyān (Geber), a Perso-Arab alchemist and pioneer in organic chemistry.
Antoine-Laurent de Lavoisier is considered the "Father of Modern Chemistry".
In his periodic table, Dmitri Mendeleev predicted the existence of 7 new elements, and placed all 60 elements known at the time in their correct places.
Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. 
Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated charge.

The word chemistry comes from a modification of the word alchemy, which referred to an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism and medicine.

Observational astronomy

Mayall telescope at Kitt Peak National Observatory
An assembly in Estonia to observe meteors
The Crab Nebula as seen in various wavelengths
Ultra HD photography taken at La Silla Observatory.
ALMA is the world's most powerful telescope for studying the Universe at submillimeter and millimeter wavelengths.
Fully-steerable radio telescope in Green Bank, West Virginia.
Skalnaté pleso observatory, Slovakia.
One of the Oldest Observatories in South America is the Quito Astronomical Observatory, founded in 1873 and located 12 minutes south of the Equator in Quito, Ecuador. The Quito Astronomical Observatory is the National Observatory of Ecuador and is located in the Historic Center of Quito and is managed by the National Polytechnic School.
An amateur astrophotography setup with an automated guide system connected to a laptop.
50 cm refracting telescope at Nice Observatory.
The main platform at La Silla hosts a huge range of telescopes with which astronomers can explore the Universe.

Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical models.

Astronomer

The Astronomer, 1668, by Johannes Vermeer
Galileo is often referred to as the Father of modern astronomy, portrait by Justus Sustermans
Portrait of the Flemish astronomer Ferdinand Verbiest who became Head of the Mathematical Board and Director of the Observatory of the Chinese emperor in 1669

An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth.

Observatory

Location used for observing terrestrial, marine, or celestial events.

The Sphinx Observatory on a mountain top in the Swiss Alps at 3,571 m
The Hubble Space Telescope in Earth's orbit
SOFIA on board a Boeing 747SP

Astronomy, climatology/meteorology, geophysical, oceanography and volcanology are examples of disciplines for which observatories have been constructed.

Ancient Greek astronomy

The Antikythera Mechanism was an analog computer from 150–100 BC designed to calculate the positions of astronomical objects.
Anaximander
Renaissance woodcut illustrating the two-sphere model.
Aristarchus's 3rd-century BCE calculations on the relative sizes of (from left) the Sun, Earth and Moon, from a 10th-century CE Greek copy
Greek equatorial sun dial, Ai-Khanoum, Afghanistan 3rd-2nd century BC.

Greek astronomy is astronomy written in the Greek language in classical antiquity.

Geocentric model

Figure of the heavenly bodies — An illustration of the Ptolemaic geocentric system by Portuguese cosmographer and cartographer Bartolomeu Velho, 1568 (Bibliothèque Nationale, Paris)
Illustration of Anaximander's models of the universe. On the left, summer; on the right, winter.
The basic elements of Ptolemaic astronomy, showing a planet on an epicycle with an eccentric deferent and an equant point. The Green shaded area is the celestial sphere which the planet occupies.
Pages from 1550 Annotazione on Sacrobosco's De sphaera mundi, showing the Ptolemaic system.
This drawing from an Icelandic manuscript dated around 1750 illustrates the geocentric model.
Phases of Venus
In this depiction of the Tychonic system, the objects on blue orbits (the Moon and the Sun) revolve around the Earth. The objects on orange orbits (Mercury, Venus, Mars, Jupiter, and Saturn) revolve around the Sun. Around all is a sphere of stars, which rotates.

In astronomy, the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded description of the Universe with Earth at the center.