James Walter "Jim" Christy (born September 15, 1938) is an American

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

known for discovering

Charon In Greek mythology, Charon or Kharon ( ; ) is a psychopomp, the ferryman of the Greek underworld. He carries the souls of those who have been given funeral rites across the rivers Acheron and Styx, which separate the worlds of the living and ...

, the largest moon of the

dwarf planet A dwarf planet is a small planetary-mass object that is in direct orbit around the Sun, massive enough to be hydrostatic equilibrium, gravitationally rounded, but insufficient to achieve clearing the neighbourhood, orbital dominance like the ...

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...

Early years

Christy was born in 1938 in

Milwaukee, Wisconsin Milwaukee is the List of cities in Wisconsin, most populous city in the U.S. state of Wisconsin. Located on the western shore of Lake Michigan, it is the List of United States cities by population, 31st-most populous city in the United States ...

. He attended the

University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a Public university, public Land-grant university, land-grant research university in Tucson, Arizona, United States. Founded in 1885 by the 13th Arizona Territorial Legislature, it ...

and earned a

Bachelor of Science A Bachelor of Science (BS, BSc, B.S., B.Sc., SB, or ScB; from the Latin ') is a bachelor's degree that is awarded for programs that generally last three to five years. The first university to admit a student to the degree of Bachelor of Scienc ...

degree in astronomy from there in 1965.

Career

On June 22, 1978 while working at the

United States Naval Observatory The United States Naval Observatory (USNO) is a scientific and military facility that produces geopositioning, navigation and timekeeping data for the United States Navy and the United States Department of Defense. Established in 1830 as the ...

, he discovered that

had a

moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

, which he named

shortly afterwards. The name remained unofficial until its adoption by the IAU in 1986.Marsden, Brian G.,
Satellites of Saturn and Pluto
', IAUC 4157 (1986 January 3) The discovery was made by carefully examining an enlargement of a photographic plate of Pluto and noticing it had a very slight bulge on one side. This plate and others had been marked "poor" because the elongated image of Pluto was thought to be a defect resulting from improper alignment. The 1965 plates included a note "Pluto image elongated", but observatory astronomers, including Christy, assumed that the plates were defective until 1978. However, Christy noticed that only Pluto was elongated—the background stars were not. His earlier work at the Naval Observatory had included photographing double stars, so it occurred to him that this bulge might be a companion of Pluto. After examining images from observatory archives dating back to 1965, he concluded that the bulge was indeed a moon. The photographic evidence was considered convincing but not conclusive (it remained possible that the bulge was due to Pluto having an unexpectedly irregular shape). However, based on Charon's calculated orbit, a series of mutual

eclipse An eclipse is an astronomical event which occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ...

s of Pluto and Charon was predicted and observed, confirming the discovery. In more modern telescopes, such as the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

or ground-based telescopes using

adaptive optics Adaptive optics (AO) is a technique of precisely deforming a mirror in order to compensate for light distortion. It is used in Astronomy, astronomical telescopes and laser communication systems to remove the effects of Astronomical seeing, atmo ...

, separate images of Pluto and Charon can be resolved, and the ''

New Horizons ''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institut ...

'' probe took images showing some of Charon's surface features. In late 2008, the

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

129564 Christy was named in his honor. As of 2015, he resides in

Flagstaff, Arizona Flagstaff ( ), known locally as Flag, is the county seat of Coconino County, Arizona, in the southwestern United States. As of the 2020 United States census, the city's population was 76,831. Flagstaff is the principal city of the Coconino Cou ...

. He has been married to Charlene Mary since 1975 and has four children. On July 14, 2015, he and

Clyde Tombaugh Clyde William Tombaugh (; February 4, 1906 – January 17, 1997) was an American astronomer best known for discovering Pluto, the first object to be identified in what would later be recognized as the Kuiper belt, in 1930. Raised on farms in ...

's children were guests at the

Johns Hopkins Applied Physics Laboratory The Johns Hopkins University Applied Physics Laboratory (or simply Applied Physics Laboratory, or APL) is a not-for-profit university-affiliated research center (UARC) in Howard County, Maryland. It is affiliated with Johns Hopkins University ...

when the ''

'' spacecraft successfully performed the first flyby of the Pluto-Charon system. Christy's inspiration for the name "Charon" came about due to a personal interest in naming the moon after his wife. He used her nickname, "Char" for Charlene, and added -on (for his interest in physics in protons and electrons, which have -on endings) to make Charon. It was only later that he found the same name in mythology, that being the ferryman who carried souls across the

Acheron River The Acheron ( or ; ''Acheron'' or Ἀχερούσιος ''Acherousios''; ''Acherontas'') is a river in the Epirus region of northwest Greece. It is long, and has a drainage area of . The river's source is located near the village Zotiko, in ...

, one of the five mythical rivers that surrounded Pluto's underworld.

References

External links

Pluto's Companion
from the website "Pluto: The Discovery of Planet X," by Brad Mager
25th Anniversary of the Discovery of Pluto's moon CHARON
from NASA JPL website {{DEFAULTSORT:Christy, James 1938 births Living people 20th-century American astronomers Discoverers of moons Discoverers of trans-Neptunian objects Charon (moon)