Astronomical Parallax 3D


General Description

This simulation illustrates the phenomenon of annual stellar parallax in astronomy. Parallax is the apparent displacement of an object relative to the background that is caused by the motion of the observer (rather than the motion of the object itself, or of the background). This simulation illustrates the parallax of an object in space that results from the Earth's annual orbital motion.

The Space View window shows the Earth (blue point) orbiting the Sun (organe point). The white point represents a stationary star. The open white circle shows the location of the object on the celestial sphere as seen from the Sun. The colored (initially magenta) point shows the location of the star on the celestial sphere as seen by an observer on the orbiting Earth. Various options allow the user to display the line of sight from Earth through the star, the line from the Sun through the star, cardinal direction arrows, the trace of the star's apparent motion, the trace of Earth's orbit, and the planes and axes of the celestial equator and ecliptic. There are also options to display plots of the apparent right ascension and declination of the star as functions of time. Controls allow the user to adjust the distance to the star as well as its celestial coordinates (as seen from the Sun). The color of the apparent star (and its traces, etc) can be changed so that multiple traces can be shown at once, each in a different color. A menu allows the user to select a particular day (equinox or solstice) of the year.

The Sky View window shows the apparent location of the star on the sky as seen by an Earth observer. The "true location" (the location as seen from the Sun) is shown as an open white circle, while the apparent location is shown as a colored disk.

Note that some features have been simplified or exaggerated. The Earth's orbit is treated as a circle. The distances to the "star" are vastly smaller than the distance to any real star (at the distance to the nearest real star the annual parallax would be imperceptible in this simulation). The size of the Earth, sun, and star are exaggerated so as to make them visible on the scale of the simulation.


Space View Frame

This frame shows a view of the Earth orbiting the sun, the star to be observed, and the "true" and apparent locations of the star on the Celestial Sphere, as seen from outside the Sphere.

Sky View Frame

This frame shows an observer's view of the "true" and apparent locations of the star as seen from Earth.

RA Plot Frame

This frame shows a plot of the apparent right ascension of the star as a function of time (with time given in years since the vernal equinox).

Dec Plot Frame

This frame shows a plot of the apparent declination of the star as a function of time (with time given in years since the vernal equinox).
Todd K. Timberlake (ttimberlake@berry.edu)