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

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

known for discovering

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

, the largest moon of the dwarf planet

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 S ...

Early years

Christy was born in 1938 in

Milwaukee, Wisconsin Milwaukee ( ), officially the City of Milwaukee, is both the most populous and most densely populated city in the U.S. state of Wisconsin and the county seat of Milwaukee County, Wisconsin, Milwaukee County. With a population of 577,222 at th ...

. He attended the

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

and earned a

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

degree in astronomy from there in 1965.

Career

On June 22, 1978 while working at the

United States Naval Observatory 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 Depo ...

, he discovered that

had a

moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

, 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 that 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 ce ...

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

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

or ground-based telescopes using adaptive optics, separate images of Pluto and Charon can be resolved, and the ''

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

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

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

129564 Christy 1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. I ...

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

Flagstaff, Arizona Flagstaff ( ) is a city in, and the county seat of, Coconino County, Arizona, Coconino County in northern Arizona, in the southwestern United States. In 2019, the city's estimated population was 75,038. Flagstaff's combined metropolitan area has ...

. He has been married to Charlene Mary since 1975 and has four children. On July 14, 2015, he and Clyde Tombaugh's children were guests at the Johns Hopkins Applied Physics Laboratory 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 (; grc, Ἀχέρων ''Acheron'' or Ἀχερούσιος ''Acherousios''; ell, Αχέροντας ''Acherontas'') is a river located in the Epirus region of northwest Greece. It is long, and its drainage area is . Its source is ...

, 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 American astronomers Discoverers of moons Discoverers of trans-Neptunian objects Charon (moon)