# Astrograph > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Astrograph > Markdown URL: https://mediated.wiki/source/Astrograph.md > Source: https://en.wikipedia.org/wiki/Astrograph > Source revision: 1182311058 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Type of telescope}} {{distinguish|Celestial cartography}} {{Use dmy dates|date=August 2021}} {{more citations needed|date=May 2014}} [[File:Lowell astrograph.jpg|thumb|150px|A {{convert|13|in|adj=on}}, f/5.3 astrograph at [Lowell Observatory](/source/Lowell_Observatory) (a refractor with a 3 element [Cooke triplet](/source/Cooke_triplet) lensTombaugh, Clyde (5 April 1995). The Struggles to Find the Ninth Planet. NASA/JPL Outer Planets/Solar Probe Project, 5 April 1995. Retrieved from http://ircamera.as.arizona.edu/NatSci102/NatSci102/text/ext9thplanet.htm.) used in the discovery of [Pluto](/source/Pluto).]] [[File:Astrograph in Heidelberg-Königstuhl.jpg|thumb|150px|A double astrograph consisting of two {{convert|6|in|adj=on}} astrographs and a central guide scope on display at [Landessternwarte Heidelberg-Königstuhl](/source/Landessternwarte_Heidelberg-K%C3%B6nigstuhl) observatory.]] [[File:Astrograph in Heidelberg-Königstuhl-2.jpg|thumb|The ''Bruce double astrograph'' at the [Landessternwarte Heidelberg-Königstuhl](/source/Landessternwarte_Heidelberg-K%C3%B6nigstuhl) observatory.]] [[File:Orion 8" Newtonian on Celestron CGEM Mount.jpg|thumbnail|This is a modern amateur [Newtonian](/source/Newtonian_telescope) astrograph, specifically designed for astrophotography.]] An '''astrograph''' (or '''astrographic camera''') is a [telescope](/source/telescope) designed for the sole purpose of [astrophotography](/source/astrophotography). Astrographs are mostly used in wide-field [astronomical survey](/source/astronomical_survey)s of the [sky](/source/sky) and for detection of [objects](/source/astronomical_object) such as [asteroid](/source/asteroid)s, [meteor](/source/meteor)s, and [comet](/source/comet)s. [Improvements in photography](/source/history_of_photography) in the middle 19th century led to designs dedicated to astrophotography, and they were also popular in the 20th century. As in other photography, chemicals were used that respond to light, recorded on a glass [photographic plate](/source/photographic_plate) or sometimes on [photographic film](/source/photographic_film). Many observatories of this period used an astrograph, beside instruments like the [transit telescope](/source/transit_instrument), [great refractor](/source/great_refractor)s, and [chronometers](/source/observatory_chronometer), or instruments for [observing the Sun](/source/Solar_astronomy). Astrographs were often used to make surveys of the [night sky](/source/night_sky), and one of the famous projects was [Carte du Ciel](/source/Carte_du_Ciel). Discoveries using an astrograph include then-planet [Pluto](/source/Pluto). Rather than looking through the telescope, it was discovered by using a [blink comparator](/source/blink_comparator) with images taken by an astrograph. By the late 20th century, electronic detectors became more common with the data being stored electronically. == Design == Most research telescopes in this class are [refractors](/source/Refracting_telescope), although there are many (usually larger) [reflecting](/source/Reflecting_telescope) designs such as the [Ritchey-Chrétien](/source/Ritchey-Chr%C3%A9tien_telescope) and [catadioptric](/source/catadioptric)s such as the [Schmidt camera](/source/Schmidt_camera). The main parameters of an Astrograph are the diameter and [f-ratio](/source/Focal_ratio) of the [objective](/source/objective_(optics)), which determine the [field of view](/source/field_of_view) and [image scale](/source/image_scale) on the photographic plate or [CCD](/source/Charge-coupled_device) detector. The objective of an astrograph is usually not very large, on the order of {{convert|20|to|50|cm|abbr=on|0}}. The shape of the focal plane is often designed to work in conjunction with a specific shaped photographic plate or CCD detector. The objective is designed to produce a particularly large (for example, {{convert|17|x|17|in}}), flat, and distortionless image at the [focal plane](/source/focal_plane). They may even be designed to focus certain wavelengths of light to match the type of film they are designed to use (early astrographs were corrected to work in blue wavelengths to match photographic emulsions of the time). Wide-angle astrographs with short f-ratios are used for photographing a huge area of sky. Astrographs with higher f-ratios are used in more precise measurements. Many observatories of the world are equipped with the so-called '''normal astrographs''' with an aperture of around {{convert|13|in}} and a focal length of {{convert|11|ft}}. The purpose of a "normal astrograph" is to create images where the scale of the image at the focal plane is a standard of approximately 60 [arcsecs](/source/Arc_minute)/mm. ==Applications== ===Astrometry=== Astrographs used in [astrometry](/source/astrometry) record images that are then used to "map" the positions of objects over a large area of the sky. These maps are then published in catalogs to be used in further study or to serve as reference points for deep-space imaging. ===Stellar classification=== Astrographs used for [stellar classification](/source/stellar_classification) sometimes consist of two identical telescopes on the same mount (a double astrograph). Each sky field can be simultaneously photographed in two colors (usually blue and yellow). Each telescope may have individually designed [non-achromatic objective](/source/non-achromatic_objective)s to focus the desired wavelength of light which is paired with the respective color-sensitive (black-and-white) photographic plate. In other cases a single telescope is used to make two exposures of the same part of the sky with different filters and color sensitive film used on each exposure. Two-color photography lets astronomers measure the color, as well as the brightness (magnitude), of each star imaged. Colors tell the star's "temperature". Knowing the color type and magnitudes lets astronomers determine the distance of a star. Sky fields that are photographed twice, decades apart in time, will reveal a nearby star's [proper motion](/source/proper_motion) when measured against the background of distant stars or galaxies. ===Discovery of astronomical objects=== By taking two exposures of the same section of the sky days or weeks apart, it is possible to find objects such as [asteroids](/source/asteroids), [meteor](/source/meteor)s, [comet](/source/comet)s, [variable star](/source/variable_star)s, [nova](/source/nova)e, and even unknown [planet](/source/planet)s. By comparing the pair of images, using a device such as a [blink comparator](/source/blink_comparator), astronomers are able to find objects that moved or changed brightness between the two exposures or simply appear in one image only, as in the case of a nova or meteor. Sometimes objects can even be found in one exposure since a fast moving object will appear as a "line" in a long exposure. One well-known case of an astrograph used in a discovery is [Clyde Tombaugh](/source/Clyde_Tombaugh)'s discovery of the [dwarf planet](/source/dwarf_planet) [Pluto](/source/Pluto) in 1930. Tombaugh was given the job of hunting for a suspected "9th planet" to be achieved by systematically photographing the area of the sky around the [ecliptic](/source/ecliptic). Tombaugh used [Lowell Observatory](/source/Lowell_Observatory)'s {{convert|13|in|adj=on}} (3 lens element), f/5.3 refractor astrograph, which recorded images on {{convert|14|x|17|in|adj=on}} glass plates. == Use in amateur astrophotography == In the [amateur astronomy](/source/amateur_astronomy) field, many types of commercial and [amateur built](/source/Amateur_telescope_making) telescopes are designed for [astrophotography](/source/astrophotography) and labeled "astrographs". Optical designs of amateur astrographs vary widely but include [apochromatic](/source/apochromatic) [refractors](/source/Refracting_telescope), variations of [Cassegrain reflector](/source/Cassegrain_reflector)s, and [Newtonian reflector](/source/Newtonian_reflector)s. Most optical designs do not produce large, flat, and well-corrected imaging fields and therefore require some type of optical correction by way of [field flatteners](/source/Field_flattener_lens) or [coma](/source/Coma_(optics)) correctors. Amateur astrographs typically have purpose-built focusers, are constructed of thermally stable materials like carbon fiber, and are put on heavy duty mounts to facilitate accurate tracking of deep sky objects for long periods of time.{{citation needed|date=July 2016}} ==See also== * [BOOTES](/source/BOOTES) * [List of telescope types](/source/List_of_telescope_types) ==References== {{reflist}} ==External links== *[http://www.astro.yale.edu/vanalten/Astrograph.html The Double Astrograph of the Yale Southern Observatory] *[http://www.ucolick.org/public/telescopes/astrograph.html The Carnegie Double Astrograph] *[https://web.archive.org/web/20060516050009/http://www.pietro.org/Astro_C5/Articles/KGraun_pluto_2003_Film.htm Pluto Imaging Challenge: Images] *[http://aanda.u-strasbg.fr:2002/articles/aas/full/1999/09/ds8335/node2.html Construction of the Tycho Reference Catalogue – 2 Source Catalogues]{{dead link|date=October 2016 |bot=InternetArchiveBot |fix-attempted=yes }} {{Commons}} Category:Telescopes Category:Cameras by type Category:Optical devices Category:Astronomical instruments [ja:天体写真儀](/source/ja%3A%E5%A4%A9%E4%BD%93%E5%86%99%E7%9C%9F%E5%84%80) --- Adapted from the Wikipedia article [Astrograph](https://en.wikipedia.org/wiki/Astrograph) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Astrograph?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.