View source for Airy-0

{{Short description|Crater on Mars whose location defines the position of the prime meridian}}
{{Infobox crater data
| titlecolor  = #FA8072
| title       = Airy-0
| image       = {{multiple image|image1=PIA25090-Mars-Airy-0-Crater-20220121.jpg |width1=215 |image2=Martian prime meridian Airy-0 crater NASA PIA03207.jpg |width2=150}}
| caption     = Airy-0 Crater from [[Mars Reconnaissance Orbiter|MRO]]; also, from A to C, [[Mariner 9]], [[Viking 1]] and [[Mars Global Surveyor]] (Airy-0 is the larger crater in top center of each frame).
| region      = Inside [[Airy (Martian crater)|Airy Crater]]
| coordinate_title = [[Mars#Geography|Coordinates]]
| globe       = Mars
| coordinates = {{coord|5.1|S|0|E|globe:mars_type:landmark|display=inline,title}}
| diameter    = {{convert|0.5|km}}
| eponym      = Sir [[George Biddell Airy]]
}}
'''Airy-0''' is a crater inside the larger [[Airy (Martian crater)|Airy Crater]] on [[Mars]], whose location historically defined the Martian [[prime meridian]]. It is about 0.5&nbsp;km (0.3&nbsp;mile) across and lies within the dark region [[Sinus Meridiani]], one of the early [[albedo feature]]s to be identified on Mars. In 2018, the [[IAU]] Working Group on Cartographic Coordinates and Rotational Elements recommended setting the longitude of the [[Viking 1#Lander|Viking 1 lander]] (47.95137° west) as the reference line.{{efn|In other words, the Martian Prime Meridian (0° longitude) is defined to be 47.95137° east of the Viking 1 lander site's [[meridian (geography)|meridian]]. The effect of the decision was to make more precise the location of the prime meridian within the 500 meter span of Airy-0.}}  This definition maintains the position of the center of Airy-0 at 0° longitude, within the tolerance of current cartographic uncertainties.<ref>{{ Citation | last1 = Archinal | first1 = B.A. | last2 = Acton  | first2 = C.H. | last3 = A'Hearn | first3 = M.F. | author3-link = Michael A'Hearn | last4 = Conrad | first4 = A. |display-authors=et al | date = 2018 | title = Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015 | journal = Celestial Mechanics and Dynamical Astronomy | volume = 130 | issue = 22 | page = 22 | doi = 10.1007/s10569-017-9805-5 | bibcode = 2018CeMDA.130...22A | s2cid = 189844155 | quote = The origin of the longitude system for Mars is now defined by assigning a longitude of 47.95137° west to the Viking 1 lander.... The longitude uncertainty within which landed resources can be determined by radiometric tracking is now ... significantly smaller than the uncertainty of determining the center of the ~500 m diameter Airy-0, the time has come to transition the orientation of the longitude system from being based on Airy-0 to the much smaller Viking 1 lander, for which there are extensive radiometric tracking data.}}</ref>

[[Merton Davies]] tied this crater into an extensive [[geodetic control network]] of the planet Mars based on [[Mariner 9]] and earlier photographs.<ref>{{ Cite web | date = 31 January 2001 | title = The Martian Prime Meridian -- Longitude "Zero" | type = MGS MOC Release No. MOC2-273 | publisher = Malin Space Science Systems | url = https://mars.jpl.nasa.gov/mgs/msss/camera/images/01_31_01_releases/airy0/ | access-date = 31 March 2018 }}</ref><ref>{{Cite book | title=Mapping Mars: Science, Imagination, and the Birth of a World | first=Oliver | last=Morton | publisher=Picador USA | location=New York | year=2002 | isbn=0-312-24551-3 | pages=[https://archive.org/details/mappingmarsscien00mort_0/page/22 22]–23 | url-access=registration | url=https://archive.org/details/mappingmarsscien00mort_0 }}</ref>  The Mariner 9 Geodesy/Cartography Group proposed that the prime meridian of Mars be defined by the center of Airy-0, which was selected by [[Harold Masursky]], [[Gerard de Vaucouleurs]], and Merton Davies at a Group meeting on 14 August 1972.<ref>{{ Citation | last1 = de Vaucouleurs | first1 = Gerard | author-link = Gerard de Vaucouleurs | last2 = Davies | first2 = Merton E. | author2-link = Merton Davies | last3 = Sturms | first3 = Francis M. Jr. | date = 1973 | title = Mariner 9 Areographic Coordinate System | journal = Journal of Geophysical Research | volume = 78 | issue = 20 | pages = 4395–4404 | doi = 10.1029/JB078i020p04395 | bibcode = 1973JGR....78.4395D }}</ref>

It was named in honor of the British [[Astronomer Royal]] Sir [[George Biddell Airy]] (1801–1892), who in 1850 built the [[transit circle]] telescope at [[Royal Observatory, Greenwich#Greenwich Meridian|Greenwich]]. The location of that telescope was subsequently chosen to define the location of Earth's prime meridian.

[[File:Meridianicropped.png|thumb|left|600px|Annotated elevation map of Opportunity landing site and some surrounding craters including Endeavour and Airy. The prime meridian is the right-hand edge of the coloured part of this image, Airy-0 is just below 5°S.]]
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==Notes==
{{notelist}}

== References ==
{{Reflist}}


== External links ==
* [http://www.google.com/mars/#lat=-5.014338&lon=0.120849&zoom=9&map=infrared&q=Airy-0%20Crater View of Airy-0 at Google Mars]
* {{cite journal |title=The location of Airy-0, the Mars prime meridian reference, from stereo photogrammetric processing of THEMIS IR imaging and digital elevation data | journal=  Journal of Geophysical Research: Planets|volume=119 |issue=12
|date=December 2014 |pages=2471{{ndash}}2486| doi=10.1002/2014JE004678 | author1=T. C. Duxbury |author2=P. Christensen |author3=D. E. Smith |author4=G. A. Neumann |author5=R. L. Kirk |author6=M. A. Caplinger |author7=A. A. Albee |author8=N. V. Seregina |author9=G. Neukum |author10=B. A. Archinal| bibcode=2014JGRE..119.2471D | s2cid=44052047 |doi-access=free }}
{{Geography of Mars}}
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[[Category:Impact craters on Mars]]
[[Category:Margaritifer Sinus quadrangle]]
[[Category:Prime meridians]]
[[Category:Sinus Sabaeus quadrangle]]