What you need to determine the current phase of Venus

Phase describes the sunlit disk we see

NASA describes Venus as showing phases, like the Moon, as its geometry relative to the Sun and Earth changes. The phase angle is measured at Venus between the directions to the Sun and the observer: Sun–Venus–observer. A phase angle near 0° corresponds to an almost fully illuminated visible disk; near 180° it is mostly dark.

The illuminated fraction describes how much of the apparent disk is lit under a spherical-body model. It is not the fraction of the whole planet receiving sunlight. Nor is it a percentage of Venus’s maximum brightness: apparent size, distance and the way its atmosphere scatters light also affect what an observer sees.

Three different angles answer three different questions

Zodiac longitude measures position around the ecliptic. Solar elongation measures the separation of Venus and the Sun from the observer’s viewpoint. Phase angle is measured at Venus instead. Confusing the location of the angle mixes up different corners of the Sun–Venus–observer triangle.

An astrological Venus–Sun aspect is another use of longitude separation; it is not an illuminated-fraction result. Retrograde or direct motion describes whether the reported zodiac longitude is decreasing or increasing. Neither a sign label nor a motion label supplies a current phase measurement.

A reliable current result needs time and full geometry

A phase calculation needs positions of the Sun, Venus and the chosen observer at a specified epoch, with consistent reference frames and light-time conventions. State whether the observer is Earth’s center or a particular surface location. The needed information is three-dimensional geometry, not just Venus’s coordinate on one reference circle.

Skyfield documents phase-angle and illuminated-fraction methods, but a library capability is not automatically a feature of this website. Sky Degrees does not calculate or validate a Venus phase result. This guide does not add that capability or assign a phase to the current date.

Common questions