An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The curve traced by a point on the circumference of a circle that rolls along a straight line. The cycloid has a → cusp at every point where it touches the straight line. The distance between cusps is 2πR, where R is the radius of the circle.

Cycloid, from Gk. kykloeides "circular," fr. kyklos "circle," → cycle + eides "form," → -oid.

Carxzâd, from carx "wheel, circle," → cycle + zâd "produced, created, born," from zâdan "give birth" (Av. zan- "to bear, give birth to a child, be born," infinitive zazâite, zâta- "born," cf. Skt. janati "begets, bears," Gk. gignesthai "to become, happen" L. gignere "to beget," gnasci "to be born," PIE base *gen- "to give birth, beget").

A curve traced by a point of a circle that rolls on the outside of a fixed circle. This curve was described by the Gk. mathematicians and astronomer Hipparchus, who made use of it to account for the apparent movement of many of the heavenly bodies.

→ epi-; → cycloid.

A curve generated by the trace of a fixed point on a small circle that rolls within a larger circle.

Hypocycloid, from → hypo- + → cycloid.