An Etymological Dictionary of Astronomy and Astrophysics

1. A small rocky object orbiting the Sun. There are millions of asteroids moving in orbits in the main → asteroid belt, between → Mars and → Jupiter and in the → Kuiper belt. The largest and the first discovered, → Ceres, about 1,000 km in size, is now classified as → dwarf planet (2006 IAU General Assembly). The largest asteroid in the solar system (Ceres apart), is → Pallas, with a size of 582 × 556 × 500 km. On the other hand, the smallest asteroid ever studied is the 2 meters space rock 2015 TC25, which was observed when it made a close flyby of Earth in October 2015. See also → near-Earth asteroid; → binary asteroid.
   

2. Math.: A → hypocycloid with four → cusps in which the → radius of the rolling → circle is a → quarter of the radius of the fixed circle. It has the → parametric equations x = a cos³θ, y = a sin³θ, where a is the radius of the fixed circle.

Etymology (EN): Gk. asteroeides “star-like,” from aster, → astro- + → -oid “like, resembling.”

Etymology (PE): Sayyârak “small planet,” from sayyâré, → planet, + -ak “diminutive suffix.”
Axtarvâr, from axtar, → astro-, + -vâr, → -oid.