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Astrophotography, also known as astronomical imaging, is
photography Photography is the art Art is a diverse range of (products of) human activities Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and int ...

photography
of
astronomical object In astronomy, an astronomical object or celestial object is a naturally occurring physical object, physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
s,
celestial event A celestial event is an astronomical Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies celestial objects and phenomena. It uses mathematics ...
s, and areas of the
night sky The term night sky, usually associated with astronomy from Earth, refers to the nighttime appearance of astronomical object, celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when ...

night sky
. The first photograph of an astronomical object (the
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

Moon
) was taken in 1840, but it was not until the late 19th century that advances in technology allowed for detailed stellar photography. Besides being able to record the details of extended objects such as the Moon,
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
, and
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
s, astrophotography has the ability to image objects invisible to the human eye such as dim
star A star is an astronomical object consisting of a luminous spheroid of plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark ...

star
s,
nebula A nebula (Latin for 'cloud' or 'fog'; pl. nebulae, nebulæ or nebulas) is a distinct body of interstellar clouds (which can consist of cosmic dust, hydrogen, helium, molecular clouds; possibly as Plasma (physics), ionized gases). Originally, th ...

nebula
e, and
galaxies A galaxy is a gravitationally bound system of star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to ...

galaxies
. This is done by long time exposure since both film and digital cameras can accumulate and sum light
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

photon
s over these long periods of time. Photography using extended exposure-times revolutionized the field of professional astronomical research, recording hundreds of thousands of new stars and nebulae invisible to the human eye. Specialized and ever-larger
optical telescopes An optical telescope is a telescope that gathers and Focus (optics), focuses light, mainly from the Visible spectrum, visible part of the electromagnetic spectrum, to create a magnification, magnified image for direct view, or to make a photograp ...
were constructed as essentially big cameras to record images on
photographic plate Photographic plates preceded photographic film Photographic film is a strip or sheet of transparent film baseA film base is a transparent substrate which acts as a support medium for the photosensitive emulsion An emulsion is a mixtu ...
s. Astrophotography had an early role in sky surveys and star classification but over time it has given way to more sophisticated equipment and techniques designed for specific fields of scientific research, with
image sensor An image sensor or imager is a sensor A sensor is a device that produces an output signal for the purpose of sensing of a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects e ...
s becoming just one of many forms of
sensor A sensor is a device that produces an output signal for the purpose of sensing of a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and s ...

sensor
. Today, astrophotography is mostly a subdiscipline in
amateur astronomy Image:Astronomy Amateur 3 V2.jpg, 250px, Amateur astronomers watch the night sky during the Perseids, Perseid meteor shower. Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the Naked e ...
, usually seeking aesthetically pleasing images rather than scientific data. Amateurs use a wide range of special equipment and techniques.


Overview

With a few exceptions, astronomical photography employs long exposures since both film and digital imaging devices can accumulate light
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

photon
s over long periods of time. The amount of light hitting the film or detector is also increased by increasing the diameter of the primary optics (the
objective Objective may refer to: * Objective (optics), an element in a camera or microscope * ''The Objective'', a 2008 science fiction horror film * Objective pronoun, a personal pronoun that is used as a grammatical object * Objective Productions, a Briti ...
) being used. Urban areas produce
light pollution Light pollution is the presence of unwanted, inappropriate, or excessive artificial lighting Lighting or illumination is the deliberate use of light Light or visible light is electromagnetic radiation within the portion of the elec ...

light pollution
so equipment and observatories doing astronomical imaging are often located in remote locations to allow long exposures without the film or detectors being swamped with stray light. Since the Earth is constantly rotating, telescopes and equipment are rotated in the opposite direction to follow the apparent motion of the stars overhead (called
diurnal motion Diurnal motion ( la, diurnus, lit=daily, from ''dies'', lit. "day") is an astronomical term referring to the apparent motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in w ...
). This is accomplished by using either
equatorial
equatorial
or computer-controlled altazimuth telescope mounts to keep celestial objects centered while the earth rotates. All
telescope mount , Merate (LC), Italy. (South support) A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope and allow for accurate pointing of the instrument. Many sorts of moun ...
systems suffer from induced tracking errors due to imperfect motor drives, the mechanical sag of the telescope, and atmospheric refraction. Tracking errors are corrected by keeping a selected aiming point, usually a ''
guide star In astronomy, a guide star is a reference star used to accurately maintain the tracking by a telescope of a heavenly body, whose motion across the sky is primarily due to the rotation of the Earth. Accurate telescope pointing and tracking is crit ...
'', centered during the entire exposure. Sometimes (as in the case of
comet A comet is an icy, small Solar System body A small Solar System body (SSSB) is an object in the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astr ...

comet
s) the object to be imaged is moving, so the telescope has to be kept constantly centered on that object. This guiding is done through a second co-mounted telescope called a "''guide scope''" or via some type of "''off-axis guider''", a device with a prism or optical
beam splitter A beam splitter (or beamsplitter) is an optical device Optics is the branch of physics that studies the behaviour and properties of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spect ...

beam splitter
that allows the observer to view the same image in the telescope that is taking the picture. Guiding was formerly done manually throughout the exposure with an observer standing at (or riding inside) the telescope making corrections to keep a
cross hair scope of a Russian Dragunov sniper rifle, SVD designated marksman rifle. A reticle, or reticule (), also known as a graticule (), is a pattern of fine lines or markings built into the eyepiece of a sighting device, such as a telescopic sight in ...
on the guide star. Since the advent of computer-controlled systems, this is accomplished by an automated system in professional and even amateur equipment. Astronomical photography was one of the earliest types of scientific photography and almost from its inception it diversified into subdisciplines that each have a specific goal including
star cartography Celestial cartography, uranography, astrography or star cartography is the aspect of astronomy and branch of cartography concerned with mapping stars, galaxies, and other astronomical objects on the celestial sphere. Measuring the position ...
,
astrometry in the optical wavelength range to determine precise positions of stars. ''Courtesy NASA/JPL-Caltech'' Astrometry is the branch of astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of ...
,
stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectr ...
,
photometryPhotometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electroma ...
,
spectroscopy Spectroscopy is the study of the interaction Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way ...

spectroscopy
,
polarimetry Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic wave Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interac ...

polarimetry
, and the discovery of astronomical objects such as
asteroids An asteroid is a minor planet A minor planet is an astronomical object in direct orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet around a star or a ...

asteroids
,
meteor A meteoroid () is a small rocky or metallic body in outer space Outer space, commonly shortened to space, is the expanse that exists beyond Earth Earth is the third planet from the Sun and the only astronomical object known to h ...

meteor
s,
comet A comet is an icy, small Solar System body A small Solar System body (SSSB) is an object in the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astr ...

comet
s,
variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either: ...
s,
nova A nova (plural novae or novas) is a transient astronomical eventA transient astronomical event, often shortened by astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field out ...

nova
e, and even unknown
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
s. These often require specialized equipment such as telescopes designed for precise imaging, for wide field of view (such as
Schmidt camera Optical ray paths inside a Schmidt camera A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope A telescope is an optical instrument using lenses, curved mirrors, or a combination of both ...
s), or for work at specific wavelengths of light. Astronomical CCD cameras may cool the sensor to reduce
thermal noise A thermal column (or thermal) is a column of rising air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of the ...
and to allow the detector to record images in other spectra such as in
infrared astronomy Infrared astronomy is a sub-discipline of astronomy which specializes in the astronomical observation, observation and analysis of astronomical objects using infrared (IR) radiation. The wavelength of infrared light ranges from 0.75 to 300 micro ...
. Specialized
filters Filter, filtering or filters may refer to: Science and technology Device * Filter (chemistry), a device which separates solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass ** Filter (aquarium), critical ...
are also used to record images in specific wavelengths.


History

The development of astrophotography as a scientific tool was pioneered in the mid-19th century for the most part by experimenters and
amateur astronomers Image:Astronomy Amateur 3 V2.jpg, 250px, Amateur astronomers watch the night sky during the Perseids, Perseid meteor shower. Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the Naked e ...
, or so-called "
gentleman scientist An independent scientist (historically also known as gentleman scientist) is a financially independent scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, area o ...
s" (although, as in other scientific fields, these were not always men). Because of the very long exposures needed to capture relatively faint astronomical objects, many technological problems had to be overcome. These included making telescopes rigid enough so they would not sag out of focus during the exposure, building clock drives that could rotate the telescope mount at a constant rate, and developing ways to accurately keep a telescope aimed at a fixed point over a long period of time. Early photographic processes also had limitations. The
daguerreotype Daguerreotype (; french: daguerréotype) was the first publicly available photographic Photography is the art, application, and practice of creating durable image An SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on ...
process was far too slow to record anything but the brightest objects, and the wet plate
collodionCollodion is a flammable, syrupy solution of nitrocellulose in Diethyl ether, ether and alcohol. There are two basic types: flexible and non-flexible. The flexible type is often used as a surgical dressing or to hold dressings in place. When painted ...
process limited exposures to the time the plate could stay wet. The first known attempt at astronomical photography was by
Louis Jacques Mandé Daguerre Louis-Jacques-Mandé Daguerre (; ; ; 18 November 1787 – 10 July 1851), better known as Louis Daguerre, was a French artist and photographer, recognized for his invention of the daguerreotype The daguerreotype (; ; french: daguerréotype) ...

Louis Jacques Mandé Daguerre
, inventor of the daguerreotype process which bears his name, who attempted in 1839 to photograph the
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

Moon
. Tracking errors in guiding the telescope during the long exposure meant the photograph came out as an indistinct fuzzy spot.
John William Draper John William Draper (May 5, 1811 – January 4, 1882) was an English-born American scientist, philosopher, physician, chemist, historian and photographer. He is credited with producing the first clear photograph of a female face (1839–40) and ...

John William Draper
, New York University Professor of Chemistry, physician and scientific experimenter managed to make the first successful photograph of the moon a year later on March 23, 1840, taking a 20-minute-long
daguerreotype Daguerreotype (; french: daguerréotype) was the first publicly available photographic Photography is the art, application, and practice of creating durable image An SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on ...
image using a
reflecting telescope A reflecting telescope (also called a reflector) is a telescope A telescope is an optical instrument An optical instrument (or "optic" for short) is a device that processes light waves (or photons), either to enhance an image for viewing ...
. The Sun may have been first photographed in an 1845 daguerreotype by the French physicists
Léon Foucault Jean Bernard Léon Foucault ( , , ; 18 September 1819 – 11 February 1868) was a French physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of ...
and
Hippolyte Fizeau Armand Hippolyte Louis Fizeau FRS FRSE MIF (23 September 181918 September 1896) was a French physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branch ...

Hippolyte Fizeau
. A failed attempt to obtain a photograph of a Total Eclipse of the Sun was made by the Italian physicist, Gian Alessandro Majocchi during an eclipse of the Sun that took place in his home city of Milan, on July 8, 1842. He later gave an account of his attempt and the Daguerreotype photographs he obtained, in which he wrote: The Sun's solar corona was first successfully imaged during the Solar eclipse of July 28, 1851. Dr. August Ludwig Busch, the Director of the Königsberg Observatory gave instructions for a local daguerreotypist named Johann Julius Friedrich Berkowski to image the eclipse. Busch himself was not present at
Königsberg Königsberg (, , ) was the name for the historic Prussian city that is now Kaliningrad, Russia. Königsberg was founded in 1255 on the site of the ancient Old Prussian settlement ''Twangste'' by the Teutonic Knights during the Northern Crusade ...

Königsberg
(now
Kaliningrad Kaliningrad ( ; rus, Калининград, p=kəlʲɪnʲɪnˈɡrat, links=y), until 1946 known as Königsberg (, ), is the largest city and the administrative centreAn administrative centre is a seat of regional administration or local gover ...

Kaliningrad
, Russia), but preferred to observe the eclipse from nearby Rixhoft. The telescope used by Berkowski was attached to Königsberg
heliometer A heliometer (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...
and had an aperture of only , and a focal length of . Commencing immediately after the beginning of totality, Berkowski exposed a daguerreotype plate for 84 seconds in the focus of the telescope, and on developing an image of the corona was obtained. He also exposed a second plate for about 40 to 45 seconds but was spoiled when the sun broke out from behind the moon. More detailed photographic studies of the Sun were made by the British astronomer starting in 1861. The first photograph of a star was a daguerreotype of the star
Vega Vega is the brightest star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun ...

Vega
by astronomer and daguerreotype photographer and experimenter John Adams Whipple, on July 16 and 17, 1850 with
Harvard College Observatory The Harvard College Observatory (HCO) is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Harvard University is a Private university, private Ivy League research ...
's 15 inch
Great refractor Great refractor refers to a large telescope with a lens, usually the largest refractor at an observatory with an equatorial mount. The preeminence and success of this style in observational astronomy defines an era in modern telescopy in the 19th ...
. In 1863 the English chemist
William Allen Miller William Allen Miller FRS (17 December 1817 – 30 September 1870) was a British scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, area of interest. In c ...
and English amateur astronomer Sir
William Huggins Sir William Huggins (7 February 1824 – 12 May 1910) was an English astronomer best known for his pioneering work in astronomical spectroscopy together with his wife Margaret Lindsay Huggins. Biography William Huggins was born at Cornhill, ...

William Huggins
used the wet collodion plate process to obtain the first ever photographic
spectrogram A spectrogram is a visual representation of the spectral density, spectrum of frequencies of a signal as it varies with time. When applied to an audio signal, spectrograms are sometimes called sonographs, voiceprints, or voicegrams. When the d ...

spectrogram
of a star,
Sirius Sirius () is the list of brightest stars, brightest star in the night sky. Its name is derived from the Ancient Greek language, Greek word (, 'glowing' or 'scorching'). The star is designated α Canis Majoris, Latinisation of name ...

Sirius
and
Capella Capella , designated α Aurigae (Latinisation of names, Latinized to Alpha Aurigae, abbreviated Alpha Aur, α Aur), is the brightest star in the constellation of Auriga (constellation), Auriga, the list of brightest stars, sixth-brigh ...
.Spectrometers, ASTROLab of Mont-Mégantic National Park
/ref> In 1872 American physician
Henry Draper Henry Draper (March 7, 1837 – November 20, 1882) was an American doctor and amateur astronomer 250px, Amateur astronomers watch the night sky during the Perseid meteor shower. Amateur astronomy is a hobby A hobby is considered to be ...

Henry Draper
, the son of John William Draper, recorded the first spectrogram of a star (Vega) to show
absorption lines A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency range, c ...
. Astronomical photography did not become a serious research tool until the late 19th century, with the introduction of
dry plate Dry plate, also known as gelatin process, is an improved type of photographic plate photographic plates, 1880 Image:Femme-au-chien neg.jpg, Negative plate Photographic plates preceded photographic film Photographic film is a strip or sheet ...
photography. It was first used by Sir William Huggins and his wife
Margaret Lindsay Huggins Margaret Lindsay, Lady Huggins (14 August 1848 in Dublin – 24 March 1915 in London), born Margaret Lindsay Murray, was an Irish-English scientific investigator and astronomer. With her husband William Huggins she was a pioneer in the field of s ...
, in 1876, in their work to record the spectra of astronomical objects. In 1880 Henry Draper used the new dry plate process with photographically corrected
refracting telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens (optics), lens as its objective (optics), objective to form an image (also referred to a dioptrics, dioptric telescope). The refracting telescope de ...
made by
Alvan Clark Alvan Clark (March 8, 1804 – August 19, 1887), born in Ashfield, Massachusetts, the descendant of a Cape Cod whaling family of English ancestry, was an American astronomy, astronomer and telescope maker. He started as a portrait painter and engr ...
to make a 51-minute exposure of the
Orion Nebula The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the Orion (constellation), constellation of Orion. It is one of the brightest nebulae, and is visible to t ...

Orion Nebula
, the first photograph of a nebula ever made. A breakthrough in astronomical photography came in 1883, when amateur astronomer
Andrew Ainslie Common Andrew Ainslie Common Fellow of the Royal Society, FRS (1841–1903) was an English amateur astronomer best known for his pioneering work in astrophotography. Biography Common was born in Newcastle Upon Tyne on 7 August 1841. His father, Thomas ...
used the dry plate process to record several images of the same nebula in exposures up to 60 minutes with a reflecting telescope that he constructed in the backyard of his home in Ealing, outside London. These images for the first time showed stars too faint to be seen by the human eye. The first all-sky photographic
astrometry in the optical wavelength range to determine precise positions of stars. ''Courtesy NASA/JPL-Caltech'' Astrometry is the branch of astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of ...
project, Astrographic Catalogue and Carte du Ciel, was started in 1887. It was conducted by 20 observatories all using special photographic telescopes with a uniform design called ''normal
astrograph observatory. File:Astrograph in Heidelberg-Königstuhl-2.jpg, The ''Bruce double astrograph'' at the Landessternwarte Heidelberg-Königstuhl observatory. An astrograph (or astrographic camera) is a telescope designed for the sole purpose of as ...
s'', all with an aperture of around and a focal length of , designed to create images with a uniform scale on the photographic plate of approximately 60 arcsecs/mm while covering a 2° × 2° field of view. The attempt was to accurately map the sky down to the 14th
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
but it was never completed. The beginning of the 20th century saw the worldwide construction of refracting telescopes and sophisticated large reflecting telescopes specifically designed for photographic imaging. Towards the middle of the century, giant telescopes such as the Hale Telescope and the Samuel Oschin telescope at
Palomar Observatory Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

Palomar Observatory
were pushing the limits of film photography. Some progress was made in the field of photographic emulsions and in the techniques of forming gas hypersensitization, cryogenic cooling, and light amplification, but starting in the 1970s after the invention of the CCD, photographic plates were gradually replaced by electronic imaging in professional and amateur observatories. CCD's are far more light sensitive, do not drop off in sensitivity over long exposures the way film does ("
reciprocity failure In photography Photography is the art Art is a diverse range of (products of) human activities involving creative imagination to express technical proficiency, beauty, emotional power, or conceptual ideas. There is no generally agreed ...
"), have the ability to record in a much wider spectral range, and simplify storage of information. Telescopes now use many configurations of CCD sensors including linear arrays and large mosaics of CCD elements equivalent to 100 million pixels, designed to cover the focal plane of telescopes that formerly used photographic plates. The late 20th century saw advances in astronomical imaging take place in the form of new hardware, with the construction of giant multi-mirror and
segmented mirror A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical mirror#Mirror shape, spherical or asymmetric (if they are part of a larger parabolic reflector). The ...
telescopes. It would also see the introduction of space-based telescopes, such as the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first ...

Hubble Space Telescope
. Operating outside the atmosphere's turbulence, scattered ambient light and the vagaries of weather allows the Hubble Space Telescope, with a mirror diameter of , to record stars down to the 30th magnitude, some 100 times dimmer than what the 5-meter Mount Palomar Hale telescope could record in 1949.


Amateur astrophotography

Astrophotography is a popular hobby among photographers and amateur astronomers. Techniques ranges from basic film and digital cameras on tripods up to methods and equipment geared toward advanced imaging. Amateur astronomers and amateur telescope makers also use homemade equipment and modified devices.


Media

Images are recorded on many types of media and imaging devices including
single-lens reflex camera A single-lens reflex camera (SLR) is a camera that typically uses a mirror and prism system (hence "reflex" from the mirror's reflection) that permits the photographer to view through the lens and see exactly what will be captured. With twin le ...
s, 35 mm film,
digital single-lens reflex camera A digital single-lens reflex camera (digital SLR or DSLR) is a digital camera A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on ph ...
s, simple amateur-level, and professional-level commercially manufactured astronomical CCD cameras,
video camera A video camera is a camera A camera is an optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural ...

video camera
s, and even off-the-shelf
webcam A webcam is a video camera A video camera is a camera A camera is an optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis ...

webcam
s adapted for long-exposure imaging. The conventional over-the-counter film has long been used for astrophotography. Film exposures range from seconds to over an hour. Commercially available color film stock is subject to reciprocal failure over long exposures, in which sensitivity to light of different wavelengths appears to drop off at different rates as the exposure time increases, leading to a color shift in the image. This is compensated for by using the same technique used in professional astronomy of taking photographs at different wavelengths that are then combined to create a correct color image. Since the film is much slower than digital sensors, tiny errors in tracking can be corrected without much noticeable effect on the final image. Film astrophotography is becoming less popular due to the lower ongoing costs, greater sensitivity, and the convenience of
digital photography Digital photography uses cameras A camera is an optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the ...
. Since the late 1990s amateurs have been following the professional observatories in the switch from film to digital CCDs for astronomical imaging. CCDs are more sensitive than film, allowing much shorter exposure times, and have a linear response to light. Images can be captured in many short exposures to create a synthetic long exposure. Digital cameras also have minimal or no moving parts and the ability to be operated remotely via an infrared remote or computer tethering, limiting vibration. Simple digital devices such as
webcam A webcam is a video camera A video camera is a camera A camera is an optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis ...

webcam
s can be modified to allow access to the focal plane and even (after the cutting of a few wires), for long exposure photography. Digital video cameras are also used. There are many techniques and pieces of commercially manufactured equipment for attaching and even basic point and shoot cameras to telescopes. Consumer-level digital cameras suffer from
image noise Image noise is random variation of brightness or color information in image An SAR radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cruz de Tenerife is visibl ...
over long exposures, so there are many techniques for cooling the camera, including
cryogenic A medium-sized dewar is being filled with liquid nitrogen by a larger cryogenic storage tank In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motio ...

cryogenic
cooling. Astronomical equipment companies also now offer a wide range of purpose-built astronomical CCD cameras complete with hardware and processing software. Many commercially available DSLR cameras have the ability to take long time exposures combined with sequential (
time-lapse Time-lapse photography is a technique in which the frequency at which film frames are captured (the frame rate) is much lower than the frequency used to view the sequence. When played at normal speed, time appears to be moving faster and thus ...
) images allowing the photographer to create a motion picture of the night sky.


Post-processing

Both digital camera images and scanned film images are usually adjusted in
image processing Digital image processing is the use of a digital computer A computer is a machine A machine is a man-made device that uses power to apply forces and control movement to perform an action. Machines can be driven by animals and people ...
software to improve the image in some way. Images can be brightened and manipulated in a computer to adjust color and increase the contrast. More sophisticated techniques involve capturing multiple images (sometimes thousands) to composite together in an additive process to sharpen images to overcome atmospheric seeing, negating tracking issues, bringing out faint objects with a poor
signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and ...
, and filtering out light pollution. Digital camera images may also need further processing to reduce the
image noise Image noise is random variation of brightness or color information in image An SAR radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cruz de Tenerife is visibl ...
from long exposures, including and a processing called ''image stacking'' or "''
Shift-and-add Image:Zeta_bootis_short_exposure.png, Typical short-exposure image of a binary star (ζ Boötis Zeta (, ; uppercase Ζ, lowercase ζ; grc, ζῆτα, el, ζήτα, label=Demotic Greek, classical or ''zē̂ta''; ''zíta'') is the sixth letter ...
''". Commercial,
freeware Freeware is software Software is a collection of Instruction (computer science), instructions that tell a computer how to work. This is in contrast to Computer hardware, hardware, from which the system is built and actually performs the work ...

freeware
and
free software Free software (or libre software) is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty ...

free software
packages are available specifically for astronomical photographic image manipulation.


Hardware

Astrophotographic hardware among non-professional astronomers varies widely since the photographers themselves range from general photographers shooting some form of aesthetically pleasing images to very serious amateur astronomers collecting data for scientific research. As a hobby, astrophotography has many challenges that have to be overcome that differ from conventional photography and from what is normally encountered in professional astronomy. Since most people live in
urban area An urban area, or built-up area, is a human settlement with a high population density and infrastructure of built environment. Urban areas are created through urbanization and are categorized by urban morphology as city, cities, towns, conurbat ...
s, equipment often needs to be portable so that it can be taken far away from the lights of major cities or towns to avoid urban
light pollution Light pollution is the presence of unwanted, inappropriate, or excessive artificial lighting Lighting or illumination is the deliberate use of light Light or visible light is electromagnetic radiation within the portion of the elec ...

light pollution
. Urban astrophotographers may use special light-pollution or narrow-band filters and advanced computer processing techniques to reduce ambient urban light in the background of their images. They may also stick to imaging bright targets like the Sun, Moon and planets. Another method used by amateurs to avoid light pollution is to set up, or rent time, on a remotely operated telescope at a dark sky location. Other challenges include setup and alignment of portable telescopes for accurate tracking, working within the limitations of “off the shelf” equipment, the endurance of monitoring equipment, and sometimes manually tracking astronomical objects over long exposures in a wide range of weather conditions. Some camera manufacturers modify their products to be used as astrophotography cameras, such as Canon's EOS 60Da, based on the EOS 60D but with a modified infrared filter and a low-noise sensor with heightened H-alpha, hydrogen-alpha sensitivity for improved capture of red hydrogen emission nebulae. There are also cameras specifically designed for amateur astrophotography based on commercially available imaging sensors. They may also allow the sensor to be cooled to reduce thermal noise in long exposures, provide raw image readout, and to be controlled from a computer for automated imaging. Raw image readout allows later better image processing by retaining all the original image data which along with stacking can assist in imaging faint deep sky objects. With very low light capability, a few specific models of
webcam A webcam is a video camera A video camera is a camera A camera is an optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis ...

webcam
s are popular for Solar, Lunar, and Planetary imaging. Mostly, these are manually focused cameras containing a CCD sensor instead of the more common CMOS. The lenses of these cameras are removed and then these are attached to telescopes to record images, videos, or both. In newer techniques, videos of very faint objects are taken and the sharpest frames of the video are 'stacked' together to obtain a still image of respectable contrast. The Philips PCVC 740K and SPC 900 are among the few webcams liked by astrophotographers. Any smartphone that allows long exposures can be used for this purpose, but some phones have a specific mode for astrophotography that will stitch together multiple exposures.


Equipment setups

;Fixed or tripod The most basic types of astronomical photographs are made with standard cameras and photographic lenses mounted in a fixed position or on a tripod. Foreground objects or landscapes are sometimes composed in the shot. Objects imaged are constellations, interesting planetary configurations, meteors, and bright comets. Exposure times must be short (under a minute) to avoid having the stars point image become an elongated line due to the Earth's rotation. Camera lens focal lengths are usually short, as longer lenses will show image trailing in a matter of seconds. A rule of thumb called the ''500 rule'' states that, to keep stars point-like, :Maximum shutter speed, exposure time in seconds = regardless of aperture or film speed, ISO setting. For example, with a 35 mm lens on an APS-C sensor, the maximum time is ≈ 9.5 s. A more accurate calculation takes into account pixel pitch and declination. Allowing the stars to intentionally become elongated lines in exposures lasting several minutes or even hours, called “star trails”, is an artistic technique sometimes used. ; Tracking mounts To achieve longer exposures without objects being blurred, some form of tracking mount is usually employed to compensate for the Earth's rotation, including commercial equatorial mounts and homemade equatorial devices such as barn door trackers and equatorial platforms. ; "Piggyback" photography Piggyback astronomical photography is a method where a camera/lens is mounted on an equatorially mounted astronomical telescope. The telescope is used as a guide scope to keep the field of view centered during the exposure. This allows the camera to use a longer exposure and/or a longer focal length lens or even be attached to some form of photographic telescope co-axial with the main telescope. ; Telescope focal plane photography In this type of photography, the telescope itself is used as the "lens" collecting light for the film or CCD of the camera. Although this allows for the magnification and light-gathering power of the telescope to be used, it is one of the most difficult astrophotography methods. This is because of the difficulties in centering and focusing sometimes very dim objects in the narrow field of view, contending with magnified vibration and tracking errors, and the added expense of equipment (such as sufficiently sturdy telescope mounts, camera mounts, camera couplers, off-axis guiders, guide scopes, illuminated cross-hairs, or auto-guiders mounted on primary telescope or the guide-scope.) There are several different ways cameras (with removable lenses) are attached to amateur astronomical telescopes including:Keith Mackay, Keith's Astrophotography and Astronomy site, Methods of Astrophotography
* Prime focus – In this method the image produced by the telescope falls directly on the film or CCD with no intervening optics or telescope eyepiece. * Positive projection – A method in which the telescope eyepiece (''eyepiece projection'') or a positive lens (placed after the focal plane of the telescope objective) is used to project a much more magnified image directly onto the film or CCD. Since the image is magnified with a narrow field of view this method is generally used for lunar and planetary photography. * Negative projection – This method, like positive projection, produces a magnified image. A negative lens, usually a Barlow lens, Barlow or a photographic teleconverter, is placed in the light cone before the focal plane of the telescope objective. * Compression – Compression uses a positive lens (also called a ''focal reducer''), placed in the converging cone of light before the focal plane of the telescope objective, to reduce overall image magnification. It is used on very long focal length telescopes, such as Maksutov telescope, Maksutovs and Schmidt–Cassegrain telescope, Schmidt–Cassegrains, to obtain a wider field of view. When the camera lens is not removed (or cannot be removed) a common method used is afocal photography, also called ''afocal projection''. In this method, both the camera lens and the telescope eyepiece are attached. When both are focused at infinity the light path between them is parallel (Afocal system, afocal), allowing the camera to basically photograph anything the observer can see. This method works well for capturing images of the moon and brighter planets, as well as narrow field images of stars and nebulae. Afocal photography was common with early 20th-century consumer-level cameras since many models had non-removable lenses. It has grown in popularity with the introduction of point and shoot digital cameras since most models also have non-removable lenses.


Remote Telescope Astrophotography

With the development of fast Internet in the last part of the 20th century along with advances in computer-controlled telescope mounts and CCD cameras 'Remote Telescope' astronomy is now a viable means for amateur astronomers not aligned with major telescope facilities to partake in research and deep-sky imaging. This enables the imager to control a telescope a large distance away in a dark location. The observers can image through the telescopes using CCD cameras. Imaging can be done regardless of the location of the user or the telescopes they wish to use. The digital data collected by the telescope is then transmitted and displayed to the user by means of the Internet. An example of a digital remote telescope operation for public use via the Internet is Bareket observatory, The Bareket Observatory.


Examples of amateur astrophotography techniques

File:Celestial tree under the milky way.JPG, 20sec exposure photograph taken with a tripod mounted DSLR camera with 18-55mm lens File:星の軌跡十津川・上湯にてImg042.jpg, Fixed tripod mounted camera capturing "star trails" File:International Space Station star trails - JSC2012E052684.jpg, Star trails photographed in earth orbit from the International Space Station File:RBerteig - Early Partial Phase (by) (1).jpg, Fixed tripod image of a solar eclipse using a digital-SLR camera with a 500 mm lens File:Fall - Late Summer Milky Way.jpg, 1 minute exposure using ISO 800 film, wide angle lens, piggybacked on an equatorial telescope File:Comet over Munich 1.jpg, Comet Hale-Bopp, camera with a 300mm lens piggybacked File:M31(Kennett).jpg, Film image of the Andromeda Galaxy shot at the prime focus of an 8" f/4 Schmidt–Newton telescope File:M8-20.jpg, Lagoon Nebula, Lagoon and Trifid Nebula, Trifid Nebulae in a montage of two film exposures with an 8" Schmidt–Newton telescope, manually guided File:Thomas Bresson - Sud-lune--2008-05-14 (by).JPG, Image of the moon taken with a Nikon Coolpix P5000 digital camera via Afocal photography, Afocal projection through an 8-inch Schmidt–Cassegrain telescope File:Afocal image of the Apennine Mountains.png, The Moon photographed using the Afocal photography, Afocal technique, using 10 seconds of video stacked to create a final image. File:Gibbous Moon.jpg, A composite of several Digital-SLR photos compiled in Adobe Photoshop, Photoshop taken via eyepiece projection from an 8-inch Schmidt Cassegrain telescope. File:Saturn-27-03-04.jpeg, Saturn image using negative projection (Barlow lens) with a
webcam A webcam is a video camera A video camera is a camera A camera is an optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis ...

webcam
attached to a 250mm Newtonian telescope. It is a composite images made from 10% of the best exposures out of 1200 images using freeware image stacking and sharpening software (Giotto) File:Afocal image of Jupiter.png, Jupiter photographed using the Afocal photography, Afocal technique, using 10 seconds of video stacked to create a final image.


See also

;Astrophotographers


References


Further reading

*
WikiHOW - ''How to Photograph the Night Sky (Astrophotography)''


External links

*
Large collection of astronomical photographs taken from the Lick Observatory from the Lick Observatory Records Digital Archive, UC Santa Cruz Library’s Digital Collections
* History of Astrophotography Timeline
1800–18601861–1900
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but seems useful. Other editors may want to decide whether this is WP:ELNO #11.-->
One of the first photos of the Sun
(taken in 1845) * Peter Abrahams
The Early History of Astrophotography
* Ricky Leon Murphy
CCD's Versus Professional Plate Film
(astronomyonline.org)

(astrosurf.com)
Astrophotography Techniques – Astropix.com



The Beauty of Space Photography
Documentary produced by Off Book (web series)
Beginners Guide to Astrophotography
(skiesandscopes.com) {{Authority control Astrophotography, Astronomical imaging Space art Photographic techniques Photography by genre Articles containing video clips