A0

A0, A-0, A₀, or a₀ may refer to:

Mathematics, science, and technology

A-0 System, an early compiler-related tool developed for electronic computers
Bohr radius (accepted mathematical symbol "a₀")
Hecke characters in number theory, previously called characters of type A₀
Haplogroup A00 and A0; see Y-chromosomal Adam and Haplogroup A (Y-DNA)
A0, a subdivision in stellar classification
Non-breaking space, which has hexadecimal representation A0 (sometimes written 0xA0) in many encoding standards

101 A0 and 103 A0, two versions of the German Heinkel Tourist moped
A-0, a 1943 pre-production model of the German Walter HWK 509 liquid-fuel bipropellant rocket engine
A-0, a 1938 variant of the German Siebel Si 204 transport and trainer aircraft
He 177 A-0, a pre-production series of the 1942 German Heinkel He 177 heavy bomber
Hs 126A-0, a variant of the 1937 German Henschel Hs 126 reconnaissance aircraft
Ju 87 A-0, a variant of the 1936 German Junkers Ju 87 dive bomber aircraft
Me 210A-0, a pre-production variant of the 1943 German Messerschmitt Me 210 heavy fighter aircraft
Isaac Peral (A-0), a Spanish submarine

A0 paper size, an international ISO 216 standard paper size (841 × 1189 mm), which results in an area very close to 1 m²
A0, the lowest A (musical note) note on a standard piano
A0, a climbing grade
A00, Irregular chess openings code in the Encyclopaedia of Chess Openings
A00, an unofficial paper size twice the size of A0 paper size
A-0 Geyser, a geyser in Yellowstone National Park
L'Avion, a French airline (IATA designator A0)