How are the planet positions computed, and how accurate are they?

The tool uses Table 1 of E. M. Standish's "Keplerian Elements for Approximate Positions of the Major Planets" from JPL, which gives each planet's semi-major axis, eccentricity, inclination, mean longitude, longitude of perihelion and longitude of the ascending node, with rates per century. For a date it computes the mean anomaly, solves Kepler's equation by Newton's method and rotates the result into J2000 ecliptic coordinates. Between 1800 and 2050 the inner planets and Mars are good to about an arcminute and opposition dates usually to within a day: fine for learning and planning, but not a substitute for a precise ephemeris.

What are opposition, conjunction and greatest elongation?

Seen from Earth, an outer planet is at opposition when it is 180° from the Sun: it is up all night, closest and brightest. Mars reaches opposition about every 26 months. At conjunction a planet lines up with the Sun and is lost in its glare. Mercury and Venus never reach opposition; they have inferior conjunction (between Earth and Sun), superior conjunction (behind the Sun) and greatest eastern and western elongations, when they stand farthest from the Sun in the evening or morning sky, the best times to see them.

What do elongation and illuminated fraction mean?

Elongation is the angle between the planet and the Sun as seen from Earth. Near 0° the planet is invisible; the larger it is the easier it is to observe, and the tool notes whether it is east (evening sky) or west (morning sky). The illuminated fraction comes from the Sun-planet-Earth phase angle: Venus is a thin crescent near inferior conjunction, while the outer planets always look nearly full (Mars never drops below about 85%).

Why does the map look crowded, or the planets tiny?

The Solar System spans a huge range: Neptune is 78 times farther from the Sun than Mercury, and the planets are minute compared with their orbits. So the planet dots are symbols, and distances can be shown on a linear or logarithmic scale. For a feel of the real proportions open 'Scale model': if the Sun were a 30 cm ball, Earth would be a 2.7 mm bead 32 m away, Neptune nearly a kilometre away, and the nearest star, Proxima Centauri, about 8,600 km away.

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☀️Solar System Simulator - Planet Positions by Date, Oppositions, Scale Model

Pick any date from 1800 to 2050 and the tool solves Kepler's equation from NASA JPL's approximate planetary elements to draw the eight planets and their orbits, viewed from above the ecliptic. Play the animation to speed through time and switch between linear and logarithmic distance views. Tap a planet to see its distance from the Sun and Earth, light time, elongation (morning or evening sky), illuminated fraction and orbital speed, plus its oppositions, conjunctions and greatest elongations over the next three years (Mars next reaches opposition on 2027-02-19). A planet data table and a 'shrink the Sun to a 30 cm ball' scale model are included.

Free · No sign-up · Runs in your browserLast updated: 2026-10-29

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How to use Solar System Simulator

1Choose a date or press 'Today', nudge it with the ±1 and ±30 day buttons, or press Play and pick a speed
2Switch the view: inner planets, out to Jupiter, everything (linear) or log distance
3Tap a planet or choose it from the list to see distances, elongation, phase and upcoming events; tap an event to jump to it
4Open 'Planet data' for radius, mass, gravity, rotation, orbital period, moons and temperature
5In 'Scale model' enter the model Sun's diameter to get each planet's model size and distance

FAQ

How are the planet positions computed, and how accurate are they?: The tool uses Table 1 of E. M. Standish's "Keplerian Elements for Approximate Positions of the Major Planets" from JPL, which gives each planet's semi-major axis, eccentricity, inclination, mean longitude, longitude of perihelion and longitude of the ascending node, with rates per century. For a date it computes the mean anomaly, solves Kepler's equation by Newton's method and rotates the result into J2000 ecliptic coordinates. Between 1800 and 2050 the inner planets and Mars are good to about an arcminute and opposition dates usually to within a day: fine for learning and planning, but not a substitute for a precise ephemeris.
What are opposition, conjunction and greatest elongation?: Seen from Earth, an outer planet is at opposition when it is 180° from the Sun: it is up all night, closest and brightest. Mars reaches opposition about every 26 months. At conjunction a planet lines up with the Sun and is lost in its glare. Mercury and Venus never reach opposition; they have inferior conjunction (between Earth and Sun), superior conjunction (behind the Sun) and greatest eastern and western elongations, when they stand farthest from the Sun in the evening or morning sky, the best times to see them.
What do elongation and illuminated fraction mean?: Elongation is the angle between the planet and the Sun as seen from Earth. Near 0° the planet is invisible; the larger it is the easier it is to observe, and the tool notes whether it is east (evening sky) or west (morning sky). The illuminated fraction comes from the Sun-planet-Earth phase angle: Venus is a thin crescent near inferior conjunction, while the outer planets always look nearly full (Mars never drops below about 85%).
Why does the map look crowded, or the planets tiny?: The Solar System spans a huge range: Neptune is 78 times farther from the Sun than Mercury, and the planets are minute compared with their orbits. So the planet dots are symbols, and distances can be shown on a linear or logarithmic scale. For a feel of the real proportions open 'Scale model': if the Sun were a 30 cm ball, Earth would be a 2.7 mm bead 32 m away, Neptune nearly a kilometre away, and the nearest star, Proxima Centauri, about 8,600 km away.

Features

JPL (Standish) approximate Keplerian elements with rates per century; Kepler's equation solved by Newton's method
Heliocentric and geocentric positions for any date from 1800 to 2050, with adjustable animation speed
Linear or logarithmic distance view, with the line of sight from Earth to the selected planet
Finds oppositions, conjunctions, inferior and superior conjunctions and greatest elongations
Physical and orbital data for all eight planets, including sunlight travel time
Scale model: model diameters and distances, plus where Proxima Centauri would be

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