zeropoint

Zeropoint, or zero-point, is a term used across disciplines to denote a baseline reference for energy, flux, or measurement from which other values are measured or calibrated.

In physics, zero-point energy is the minimum possible energy of a quantum mechanical system in its ground state. Even at absolute zero, systems retain motion due to the Heisenberg uncertainty principle. The canonical example is the quantum harmonic oscillator, whose ground-state energy is nonzero. Zero-point energy gives rise to observable effects such as the Casimir effect, and it features in discussions of cosmology and fundamental physics. It is not large enough to provide practical energy.

In astronomy and astrophotography, zeropoint refers to the calibration constant that converts a measured flux or instrumental magnitude into a standard photometric system magnitude. Determination involves observing standard stars and accounting for instrument throughput, filter transmission, and atmospheric conditions. The zeropoint can vary with time and observing conditions and is essential for comparing measurements across datasets.

In instrumentation and metrology, a zero-point offset is the value read by a sensor when the true input is zero. This offset must be subtracted to obtain accurate measurements, and calibrations are often used to track drift over time.

The term is also used in other measurement contexts to denote a baseline or reference level, including electronic, gravitational, and environmental sensors. The specific meaning depends on the discipline and context. See also zero-point magnitude, zero-point energy, and zero-point offset for related concepts.