Apsides are a term used in astronomy and physics to describe the two extreme points in an orbit of a celestial body. These points are the closest and farthest points from the center of mass of the body being orbited. The concept of apsides is essential in understanding the motion of celestial bodies and their interactions with each other.
Definitions
The term apsides comes from the Greek word apsis, which means arch or vault. In astronomy, apsides refer to the two points in an elliptical orbit where the orbiting body is closest or farthest from the body being orbited. The point of closest approach is called the perigee, while the point of farthest distance is called the apogee.
Origin
The concept of apsides has been known since ancient times. Early astronomers and mathematicians, such as Hipparchus and Ptolemy, studied the motion of celestial bodies and recognized the importance of the apsides in understanding their orbits. The term apsis was first used by the Greek astronomer and mathematician Apollonius of Perga in the 3rd century BCE.
Meaning in different dictionaries
In the Merriam-Webster Dictionary, apsides are defined as “either of the two points on an orbit that are nearest to and farthest from the center of attraction.” The Oxford English Dictionary defines apsides as “the two points in the orbit of a planet or other celestial body at which it is closest to and farthest from the body around which it revolves.”
Associations
Apsides are closely related to the concept of orbital eccentricity, which is a measure of how elliptical an orbit is. The more elliptical an orbit, the greater the difference between the perigee and apogee. Apsides are also important in understanding the gravitational interactions between celestial bodies, such as the Moon and Earth.
Synonyms
Other terms that can be used to describe apsides include perihelion and aphelion, which refer specifically to the closest and farthest points in an orbit around the Sun. Periapsis and apoapsis are also used to describe the closest and farthest points in any orbit.
Antonyms
There are no direct antonyms for apsides, as the term refers specifically to the two extreme points in an orbit. However, the term apocenter can be used to describe the farthest point in an orbit, while the term pericenter can be used to describe the closest point.
The same root words
The root word apsis is also used in other scientific terms, such as apse, which refers to a semicircular or polygonal recess in a building, and apsidal, which refers to anything related to or resembling an apse.
Example Sentences
- The Moon’s perigee and apogee are approximately 225,623 miles and 251,000 miles from Earth, respectively.
- The spacecraft will reach its apoapsis in three hours, at which point it will begin its descent back towards Earth.
- The apsidal vaults in the cathedral are some of the most impressive examples of Gothic architecture in the world.