Perihelische

Perihelische is an adjective used in astronomy to refer to things related to perihelion, the closest point of a body's orbit to the Sun. The term is commonly found in Dutch-language astronomical writing, where perihelische describes phenomena, measurements, or properties associated with the Sun’s proximity. Its English equivalents are perihelion, perihelial, or perihelian, but perihelische reflects the Dutch usage.

In orbital mechanics, perihelische quantities describe the state of an object at perihelion. For an elliptical orbit with semi-major axis a and eccentricity e, the perihelion distance is q = a(1 − e). The orbital speed at perihelion is v_peri = sqrt( μ (1 + e) / (a (1 − e)) ), where μ is the Sun’s standard gravitational parameter. These relationships arise from the vis-viva equation v^2 = μ(2/r − 1/a) evaluated at r = q.

Perihelische considerations are important for interpreting observational data and orbital evolution. Objects are typically brightest near perihelion due to reduced solar distance, and gravitational perturbations can shift the exact timing of perihelion passages over long timescales. Examples include Mercury, whose perihelion lies about 0.3075 astronomical units from the Sun, and Halley’s Comet, with a perihelion distance of roughly 0.586 AU.

See also: perihelion, aphelion, orbital elements,Vis-viva equation.