Apohele

I learned a new word—Apohele. You say AH-POE-HAY-LAY, and would it surprise you that it is from Hawaiian? It means “orbit” and is an unofficial name for a group of asteroids that are also called  Atiras.

Atira is more official because it has generally been the custom in astronomy to name similar objects after the first of those objects to be spotted and recognized. The first in the class was asteroid 163693 found in 2003. The newest member of the class is 2019 LF6. This recently-found asteroid is about a kilometer across and travels around the Sun in 151 days, the shortest “year” of any non-planet object. Mercury’s year is 88 days while Venus’ is 225 days. (Check out the graphic below.)

There are about twenty such Apohele known. All of them orbit the Sun within the Earth’s orbit, which makes them unusual. Orbits are elliptical so they have a far point (aphelion) and a near point (perihelion). Apohele have aphelions less than Earth’s perihelion.

NEAs or Near Earth Asteroids are broken into three other groups: Amors, Apollos, and Atens. Amors are outside of Earth’s solar path but within Mars’ orbit. Apollos and Atens cross the Earth’s orbit but vary in orbital size. To get technical, Apollos have a semi-major axis larger than Earth’s, and Atens have a semi-major axis smaller than Earth’s. (You might remember such things from high school math.) All are names from mythology—Atira is a Pawnee goddess.

So which one do you like better: Atira or Apohele?

2019lf6_orbit_mar82020

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