Harold F. Levison
Encyclopedia
Harold F. "Hal" Levison is a planetary scientist specializing in planetary dynamics. He argued for a distinction between what are now called dwarf planet
s and the other eight planet
s based on their inability to "clear the neighborhood around their orbits
", although his proposal suggested the terms "unterplanet" and "überplanet" and used the word "dwarf" to mean something else. Among other distinctions, he is the co-author of SWIFT, a commonly used symplectic integrator that solves planetary equations of motion for periods of billions
of years. He currently works at the Southwest Research Institute
, Texas
, and studies planetary orbits and their evolution through solar system
history.
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...
s and the other eight planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s based on their inability to "clear the neighborhood around their orbits
Clearing the neighbourhood
"Clearing the neighbourhood of its orbit" is a criterion for a celestial body to be considered a planet in the Solar System. This was one of the three criteria adopted by the International Astronomical Union in its 2006 definition of planet....
", although his proposal suggested the terms "unterplanet" and "überplanet" and used the word "dwarf" to mean something else. Among other distinctions, he is the co-author of SWIFT, a commonly used symplectic integrator that solves planetary equations of motion for periods of billions
1000000000 (number)
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....
of years. He currently works at the Southwest Research Institute
Southwest Research Institute
Southwest Research Institute , headquartered in San Antonio, Texas, is one of the oldest and largest independent, nonprofit, applied research and development organizations in the United States...
, Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, and studies planetary orbits and their evolution through solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
history.