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Collection:
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NASA Planetary Photo Journal Collection
Collection
NASA Planetary Photo Journal Collection
Collection
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Title:
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The Martian Prime Meridian -- Longitude "Zero
Title
The Martian Prime Meridian -- Longitude "Zero
Title
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Original Caption Released with Image:
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Original_Caption_Rel eased_with_Image
Original Caption Released with Image
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Original Caption Released with Image:
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On Earth, the longitude of the Royal Observatory in Greenwich, England is defined as the "prime meridian," or the zero point of longitude. Locations on Earth are measured in degrees east or west from this position. The prime meridian was defined by international agreement in 1884 as the position of the large "transit circle," a telescope in the Observatory's Meridian Building. The transit circle was built by Sir George Biddell Airy, the 7th Astronomer Royal, in 1850. (While visual observations with transits were the basis of navigation until the space age, it is interesting to note that the current definition of the prime meridian is in reference to orbiting satellites and Very Long Baseline Interferometry (VLBI) measurements of distant radio sources such as quasars. This "International Reference Meridian" is now about 100 meters east of the Airy Transit at Greenwich.)
For Mars, the prime meridian was first defined by the German astronomers W. Beer and J. H. Mädler in 1830-32. They used a small circular feature, which they designated "a," as a reference point to determine the rotation period of the planet. The Italian astronomer G. V. Schiaparelli, in his 1877 map of Mars, used this feature as the zero point of longitude. It was subsequently named Sinus Meridiani ("Middle Bay") by Camille Flammarion.
When Mariner 9 mapped the planet at about 1 kilometer (0.62 mile) resolution in 1972, an extensive "control net" of locations was computed by Merton Davies of the RAND Corporation. Davies designated a 0.5-kilometer-wide crater (0.3 miles wide), subsequently named "Airy-0" (within the large crater Airy in Sinus Meridiani) as the longitude zero point. (Airy, of course, was named to commemorate the builder of the Greenwich transit.) This crater was imaged once by Mariner 9 (the 3rd picture taken on its 533rd orbit, 533B03) and once by the Viking 1 orbiter in 1978 (the 46th image on that spacecraft's 746th orbit, 746A46), and these two images were the basis of the martian longitude system for the rest of the 20th Century.
The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) has attempted to take a picture of Airy-0 on every close overflight since the beginning of the MGS mapping mission. It is a measure of the difficulty of hitting such a small target that nine attempts were required, since the spacecraft did not pass directly over Airy-0 until almost the end of the MGS primary mission, on orbit 8280 (January 13, 2001).
In the left figure above, the outlines of the Mariner 9, Viking, and Mars Global Surveyor images are shown on a MOC wide angle context image, M23-00924. In the right figure, sections of each of the three images showing the crater Airy-0 are presented. A is a piece of the Mariner 9 image, B is from the Viking image, and C is from the MGS image. Airy-0 is the larger crater toward the top-center in each frame.
The MOC observations of Airy-0 not only provide a detailed geological close-up of this historic reference feature, they
Original_Caption_Rel eased_with_Image
On Earth, the longitude of the Royal Observatory in Greenwich, England is defined as the "prime meridian," or the zero point of longitude. Locations on Earth are measured in degrees east or west from this position. The prime meridian was defined by international agreement in 1884 as the position of the large "transit circle," a telescope in the Observatory's Meridian Building. The transit circle was built by Sir George Biddell Airy, the 7th Astronomer Royal, in 1850. (While visual observations with transits were the basis of navigation until the space age, it is interesting to note that the current definition of the prime meridian is in reference to orbiting satellites and Very Long Baseline Interferometry (VLBI) measurements of distant radio sources such as quasars. This "International Reference Meridian" is now about 100 meters east of the Airy Transit at Greenwich.)
For Mars, the prime meridian was first defined by the German astronomers W. Beer and J. H. Mädler in 1830-32. They used a small circular feature, which they designated "a," as a reference point to determine the rotation period of the planet. The Italian astronomer G. V. Schiaparelli, in his 1877 map of Mars, used this feature as the zero point of longitude. It was subsequently named Sinus Meridiani ("Middle Bay") by Camille Flammarion.
When Mariner 9 mapped the planet at about 1 kilometer (0.62 mile) resolution in 1972, an extensive "control net" of locations was computed by Merton Davies of the RAND Corporation. Davies designated a 0.5-kilometer-wide crater (0.3 miles wide), subsequently named "Airy-0" (within the large crater Airy in Sinus Meridiani) as the longitude zero point. (Airy, of course, was named to commemorate the builder of the Greenwich transit.) This crater was imaged once by Mariner 9 (the 3rd picture taken on its 533rd orbit, 533B03) and once by the Viking 1 orbiter in 1978 (the 46th image on that spacecraft's 746th orbit, 746A46), and these two images were the basis of the martian longitude system for the rest of the 20th Century.
The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) has attempted to take a picture of Airy-0 on every close overflight since the beginning of the MGS mapping mission. It is a measure of the difficulty of hitting such a small target that nine attempts were required, since the spacecraft did not pass directly over Airy-0 until almost the end of the MGS primary mission, on orbit 8280 (January 13, 2001).
In the left figure above, the outlines of the Mariner 9, Viking, and Mars Global Surveyor images are shown on a MOC wide angle context image, M23-00924. In the right figure, sections of each of the three images showing the crater Airy-0 are presented. A is a piece of the Mariner 9 image, B is from the Viking image, and C is from the MGS image. Airy-0 is the larger crater toward the top-center in each frame.
The MOC observations of Airy-0 not only provide a detailed geological close-up of this historic reference feature, they
Original Caption Released with Image
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Original Caption Released with Image:
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will be used to improve our knowledge of the locations of all features on Mars, which will in turn enable more precise landings on the Red Planet by future spacecraft and explorers.
Original_Caption_Rel eased_with_Image
will be used to improve our knowledge of the locations of all features on Mars, which will in turn enable more precise landings on the Red Planet by future spacecraft and explorers.
Original Caption Released with Image
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Image Credit:
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NASA/JPL/MSSS
Image_Credit
NASA/JPL/MSSS
Image Credit
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Produced By:
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Malin Space Science Systems
Produced_By
Malin Space Science Systems
Produced By
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Mission:
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Mars Global Surveyor (MGS)
Mission
Mars Global Surveyor (MGS)
Mission
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Spacecraft:
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Mars Global Surveyor Orbiter
Spacecraft
Mars Global Surveyor Orbiter
Spacecraft
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Target Name:
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Mars
Target_Name
Mars
Target Name
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Is a satellite of:
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Sol (our sun)
Is_a_satellite_of
Sol (our sun)
Is a satellite of
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Instrument:
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Mars Orbiter Camera
Instrument
Mars Orbiter Camera
Instrument
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Product Size:
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1029 samples x 909 lines
Product_Size
1029 samples x 909 lines
Product Size
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Primary Data Set:
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MGS EDRs
Primary_Data_Set
MGS EDRs
Primary Data Set
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Producer ID:
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MOC2-273
Producer_ID
MOC2-273
Producer ID
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facet_what:
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Sun
facet_what
Sun
facet_what
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facet_what:
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Mariner
facet_what
Mariner
facet_what
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facet_what:
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Crater
facet_what
Crater
facet_what
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facet_what:
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Earth
facet_what
Earth
facet_what
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facet_what:
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Mars
facet_what
Mars
facet_what
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facet_what:
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Viking
facet_what
Viking
facet_what
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facet_what:
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Meridian
facet_what
Meridian
facet_what
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facet_what:
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Viking 1 Orbiter
facet_what
Viking 1 Orbiter
facet_what
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facet_what:
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Surveyor
facet_what
Surveyor
facet_what
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facet_what:
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Mariner 9
facet_what
Mariner 9
facet_what
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facet_what:
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Mars Global Surveyor Orbiter (MGS)
facet_what
Mars Global Surveyor Orbiter (MGS)
facet_what
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facet_what:
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Mars Orbiter Camera (MOC)
facet_what
Mars Orbiter Camera (MOC)
facet_what
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facet_where:
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Mars
facet_where
Mars
facet_where
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facet_where:
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Jet Propulsion Laboratory (JPL)
facet_where
Jet Propulsion Laboratory (JPL)
facet_where
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facet_when:
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1972
facet_when
1972
facet_when
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facet_when:
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1978
facet_when
1978
facet_when
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facet_when:
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1884
facet_when
1884
facet_when
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facet_when:
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1850
facet_when
1850
facet_when
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facet_when:
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1830
facet_when
1830
facet_when
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facet_when:
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20th Century
facet_when
20th Century
facet_when
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facet_when:
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January 13, 2001
facet_when
January 13, 2001
facet_when
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facet_when_year:
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1972
facet_when_year
1972
facet_when_year
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facet_when_year:
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1978
facet_when_year
1978
facet_when_year
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facet_when_year:
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2001
facet_when_year
2001
facet_when_year
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facet_when_year:
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1884
facet_when_year
1884
facet_when_year
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facet_when_year:
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1850
facet_when_year
1850
facet_when_year
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facet_when_year:
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1830
facet_when_year
1830
facet_when_year
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Image #:
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PIA03207
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UID:
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SPD-PHOTJ-PIA03207
UID
SPD-PHOTJ-PIA03207
UID
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orignial url:
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orignial_url
orignial url
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