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.

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.

- Observational astronomy

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Outline of space science

Provided as an overview and topical guide to space science:

A laser-guided observation of the Milky Way Galaxy at the Paranal Observatory in Chile in 2010
The diversity found in the different types and scales of astronomical objects make the field of study increasingly specialized.
A proposed timeline of the origin of space, from physical cosmology
Astronaut Piers Sellers during the third spacewalk of STS-121, a demonstration of orbiter heat shield repair techniques

Observational astronomy – Observatories on the ground as well as space observatories take measurements of celestial entities and phenomena

Infrared astronomy

Carina Nebula in infrared light captured by the Hubble Space Telescope's Wide Field Camera 3.
Hubble's ground-breaking near-infrared NICMOS
SOFIA is an infrared telescope in an aircraft, shown here in a 2009 test
High on the Chajnantor Plateau, the Atacama Large Millimeter Array provides an extraordinary place for infrared astronomy.
Hubble infrared view of the Tarantula Nebula.
Artist impression of galaxy W2246-0526, a single galaxy glowing in infrared light as intensely as 350 trillion Suns.
Atmospheric windows in the infrared.

Infrared astronomy is a sub-discipline of astronomy which specializes in the observation and analysis of astronomical objects using infrared (IR) radiation.

Astronomy

Natural science that studies celestial objects and phenomena.

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.

In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars.

Optical telescope

Telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electronic image sensors.

The Large Binocular Telescope uses two curved mirrors to gather light
Schematic of a Keplerian refracting telescope. The arrow at (4) is a (notional) representation of the original image; the arrow at (5) is the inverted image at the focal plane; the arrow at (6) is the virtual image that forms in the viewer's visual sphere. The red rays produce the midpoint of the arrow; two other sets of rays (each black) produce its head and tail.
Eight-inch refracting telescope at Chabot Space and Science Center
The Keck II telescope gathers light by using 36 segmented hexagonal mirrors to create a 10 m (33 ft) aperture primary mirror
These eyes represent a scaled figure of the human eye where 15 px = 1 mm, they have a pupil diameter of 7 mm. Figure A has an exit pupil diameter of 14 mm, which for astronomy purposes results in a 75% loss of light. Figure B has an exit pupil of 6.4 mm, which allows the full 100% of observable light to be perceived by the observer.
Two of the four Unit Telescopes that make up the ESO's VLT, on a remote mountaintop, 2600 metres above sea level in the Chilean Atacama Desert.
Comparison of nominal sizes of primary mirrors of some notable optical telescopes
Harlan J. Smith Telescope reflecting telescope at McDonald Observatory, Texas

People use optical telescopes (including monoculars and binoculars) for outdoor activities such as observational astronomy, ornithology, pilotage, hunting and reconnaissance, as well as indoor/semi-outdoor activities such as watching performance arts and spectator sports.

Gamma-ray astronomy

Survey of the sky at energies above 1 GeV, collected by the Fermi Gamma-ray Space Telescope in five years of observation (2009 to 2013).
The sky at energies above 100 MeV observed by the Energetic Gamma Ray Experiment Telescope (EGRET) of the Compton Gamma Ray Observatory (CGRO) satellite (1991–2000).
The Moon as seen by the Energetic Gamma Ray Experiment Telescope (EGRET), in gamma rays of greater than 20 MeV. These are produced by cosmic ray bombardment of its surface.
Compton released into orbit by the Space Shuttle, 1991
Concept of two gigantic gamma-ray bubbles at the heart of the Milky Way.

Gamma-ray astronomy is the astronomical observation of gamma rays, the most energetic form of electromagnetic radiation, with photon energies above 100 keV.

Theoretical astronomy

Use of analytical and computational models based on principles from physics and chemistry to describe and explain astronomical objects and astronomical phenomena.

Historical accuracy of atomic clocks from NIST.

Theoretical astronomy is built on the work of observational astronomy, astrometry, astrochemistry, and astrophysics.

Galileo Galilei

Italian astronomer, physicist and engineer, sometimes described as a polymath, from the city of Pisa, then part of the Duchy of Florence.

1636 portrait by Justus Sustermans
Galileo's elder daughter Virginia was particularly devoted to her father
Galileo's "cannocchiali" telescopes at the Museo Galileo, Florence
An illustration of the Moon from Sidereus Nuncius, published in Venice, 1610
It was on this page that Galileo first noted an observation of the moons of Jupiter. This observation upset the notion that all celestial bodies must revolve around the Earth. Galileo published a full description in Sidereus Nuncius in March 1610
The phases of Venus, observed by Galileo in 1610
Galileo Galilei, portrait by Domenico Tintoretto
Cristiano Banti's 1857 painting Galileo facing the Roman Inquisition
Portrait of Galileo Galilei by Justus Sustermans, 1636. Uffizi Museum, Florence.
Portrait, originally attributed to Murillo, of Galileo gazing at the words "E pur si muove" (And yet it moves) (not legible in this image) scratched on the wall of his prison cell. The attribution and narrative surrounding the painting have since been contested.
Tomb of Galileo, Santa Croce, Florence
Middle finger of Galileo's right hand
A replica of the earliest surviving telescope attributed to Galileo Galilei, on display at the Griffith Observatory
Galileo's geometrical and military compass, thought to have been made c. 1604 by his personal instrument-maker Marc'Antonio Mazzoleni
The earliest known pendulum clock design. Conceived by Galileo Galilei
Galileo e Viviani, 1892, Tito Lessi
Dome of the Cathedral of Pisa with the "lamp of Galileo"
Galileo showing the Doge of Venice how to use the telescope (fresco by Giuseppe Bertini)
Statue outside the Uffizi, Florence
Statue of Galileo by Pio Fedi (1815–1892) inside the Lanyon Building of the Queen's University of Belfast. Sir William Whitla (Professor of Materia Medica 1890–1919) brought the statue back from Italy and donated it to the university.

Galileo has been called the "father" of observational astronomy, modern physics, the scientific method, and modern science.

Astrometry

Branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies.

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.

In observational astronomy, astrometric techniques help identify stellar objects by their unique motions.

Double star

Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.
Artist's impression of the discs around the young stars HK Tauri A and B.

In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.

Apparent magnitude

Measure of the brightness of a star or other astronomical object observed from Earth.

Asteroid 65 Cybele and two stars, with their magnitudes labeled
Image of 30 Doradus taken by ESO's VISTA. This nebula has a visual magnitude of 8.
Graph of relative brightness versus magnitude

But in observational astronomy and popular stargazing, unqualified references to "magnitude" are understood to mean apparent magnitude.