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

1) Math.: A portion of a real line (i.e. a line with a fixed scale so that every real number corresponds to a unique point on the line) between two designated endpoints. → span.
2) Music: Difference in pitch between two tones of a scale.

From O.Fr. intervalle, from L.L. intervallum, originally "space between two palisades or ramparts," from → inter- "between" + vallum "rampart."

Andarvâr, literally "between walls," from andar-→ inter- + vâr "wall," as in divâr "wall" (originally "fortress wall," from *dida-vāra-), variant bâru "wall, rampart, fortification; fort; tower;" Mid.Pers. bâr, var "enclosure, defences, fortress;" Av. var- "castle."

The space-time interval between two events if it is zero, i.e. ds² = 0.

→ lightlike; → interval.

An interval that does not include its two endpoints.

→ open; → interval.

1) In Einstein's → theory of relativity, ds² = c²dt² - dx² - dy² - dz².
2) In → Newtonian mechanics, time interval: dt; space interval at fixed time: dl² = dx² + dy² + dz².

→ space-time; → interval.

The → space-time interval between two → events if it is imaginary, i.e. ds²< 0.

→ spacelike; → interval.

The → space-time interval between two → events if it is real, i.e. ds² > 0.

→ timelike; → interval.