Elongation of Mercury and Venus
Revolutions of Mercury, Venus and Earth around the Sun are shown in this animation. Radii of their orbits, which are approximated by circles (not far from the truth) are scaled relatively according to their average distances from the Sun. Measured periods of the planets are taken into account. We assume that all three planets are aligned along the same line at time t=0, as shown in the beginning situation. Units for time are days (as measured on the Earth).
ELONGATION is the angle between directions from the observer on Earth towards the Sun (the green line) and from the observer towards the observed planet (to Mercury - yellow line - and to Venus - magenta line). Check the box of the planet you will observe. A graph is drawn, which shows how the elongation changes with time.
Barbara Rovšek, december 2016