Overview
Ephemeris is a real-time, browser-based solar system explorer built
with WebGL. It renders the positions of planets, moons, dwarf planets,
asteroids, comets, spacecraft, and other bodies as they actually move
through space, not as static illustrations.
Orbital mechanics are computed using Kepler's equations: each body
follows a true elliptical orbit, with the Sun at one focus. Positions
are calculated from J2000.0 epoch data sourced from NASA's Jet
Propulsion Laboratory. The simulation clock can run forward or
backward at any speed, from a single day per second to centuries.
Distances and sizes can be shown in two modes: artistic scale,
where body sizes are exaggerated for visibility, and true scale,
where everything is rendered at its actual relative size. In true scale,
planets become near-invisible points against the vast emptiness between
them.
Note: orbital elements are mean elements, not
osculating. This means positions are accurate to within a few
arcseconds for the inner planets over centuries, and within degrees
for the outer solar system. Precision degrades for highly perturbed
objects such as Jupiter-family comets.
Object types
Planets
The eight major planets from Mercury to Neptune, with surface
textures, ring systems where applicable, and all their natural
satellites and orbiting spacecraft.
Dwarf planets
IAU-classified dwarf planets: Pluto, Eris, Makemake, Haumea,
and Ceres, plus additional large trans-Neptunian objects such as
Sedna, Quaoar, and Gonggong.
Comets
Short and long-period comets with highly eccentric orbits.
Near perihelion, rendered ion and dust tails point away from
the Sun. Includes Halley, Hale-Bopp, 12P/Pons-Brooks, and
C/2024 G3 ATLAS.
Asteroids
Named main belt asteroids and near-Earth objects: Vesta,
Pallas, Kleopatra, Apophis, Bennu, Ryugu, 2024 YR4, and
hundreds more.
Hazardous asteroids
Potentially Hazardous Asteroids (PHAs): bodies with a
minimum orbit intersection distance ≤ 0.05 AU with Earth.
Named objects with individual descriptions.
KBO / TNO
Trans-Neptunian objects in the Kuiper Belt and the scattered
disc, including resonant objects and detached bodies beyond
Neptune's orbit.
Centaurs
Small bodies with unstable orbits crossing those of the giant
planets, gravitationally perturbed objects between the outer
solar system and the inner regions.
Trojans
Asteroids at the L4 and L5 Lagrange points of Jupiter and
Neptune. Named objects and particle clouds, including Lucy
mission targets.
Spacecraft
Active and historic missions including Voyager 1 & 2,
New Horizons, JWST, Parker Solar Probe, BepiColombo, JUICE,
Hera, and rovers on Mars.
Interstellar objects
Bodies from outside the solar system on hyperbolic
trajectories: ʻOumuamua (2017), Borisov (2019), and
3I/ATLAS (2025).
Nearby stars
Stars within roughly 10 light-years shown as background
reference points: Alpha Centauri, Barnard's Star, Sirius,
and others.
Display
Orbit lines
Elliptical orbit path for each body.
Labels
Name tags above each body. Labels are hidden automatically when occluded by a planet.
Trails
Live accumulating trail behind each body as the simulation runs.
Rotation axes
The spin axis of each planet and dwarf planet, revealing axial tilt: Earth 23°, Uranus 98°, Venus 177°.
Ecliptic plane
Polar grid showing the plane of Earth's orbit, used as the reference plane of the solar system.
Perihelion / Aphelion
Markers for the closest and farthest points of each planetary orbit.
Hill spheres
The gravitational sphere of influence around each planet, where its gravity dominates over the Sun.
Phenomena
Zodiac
The 12 zodiac constellations along the ecliptic, with connecting lines.
IAU constellations
All 88 officially recognised constellations with connecting lines and labels.
Messier catalogue
110 deep-sky objects catalogued by Charles Messier in the 18th century: galaxies, nebulae, and clusters.
Asteroid belt
Particle cloud representing the main asteroid belt between Mars and Jupiter.
Kuiper belt
Particle cloud representing the Kuiper belt beyond Neptune's orbit.
Trojan clouds
Particle clouds at the L4 and L5 Lagrange points of Jupiter (~7,000 known) and Neptune.
Earth-crossing asteroids
All 27,000+ Aten, Apollo, and Atira asteroids from the JPL Small-Body Database, computed in real time and cached for seven days.
Parker spiral
The interplanetary magnetic field shaped into a spiral by the Sun's rotation.
Heliosphere
The bubble of solar wind: termination shock, heliopause, and the theoretical Oort cloud boundary.
Solar wind
Stream of charged particles from the Sun, with live data from NASA OMNI when available.
Magnetic field
Simplified dipole magnetic field lines around magnetised planets.
Planetary events
Oppositions and conjunctions marked on the timeline.
Eclipses
Solar and lunar eclipses marked on the timeline.
Solstices / Equinoxes
The four seasonal turning points marked on the timeline with colored ticks: spring (green), summer (yellow), autumn (orange), and winter (blue). These mark Earth's position at key points in its orbit: the equinoxes when day and night are equal length, and the solstices when daylight is longest or shortest.
User Guide
Navigation
Left drag
Rotate the view around the current focus point
Right drag
Pan the camera
Scroll
Zoom in / out
Click body
Focus on that object and open its info panel
Click space
Deselect and return to free navigation
1 – 8
Fly directly to Mercury through Neptune
Esc
Return to overview, deselect all
Time controls
Space
Pause / resume simulation
Speed slider
Drag to adjust simulation speed (logarithmic scale)
1d/s · 1y/s · 1c/s
Jump to preset speeds: day, year, or century per second
Date field
Click to open calendar picker; type a date in dd-mm-yyyy format to jump
T
Jump to today
Timeline
Drag the bar at the bottom to scrub through time; shows conjunctions, oppositions, eclipses, solstices, and equinoxes
Search
/ or Ctrl+F
Open the search bar
Enter
Select the first result and fly to it
Esc
Close the search bar
Layers panel
The panel on the left shows all available object categories and
visual overlays. Toggle layers on or off individually, or use
none to switch everything off at once.
F
Collapse / expand the layers panel
L
Toggle all labels
O
Toggle all orbit lines
S
Toggle between artistic and true scale
G
Toggle the galaxy map overlay
Tools
Found at the bottom of the layers panel under Tools.
Spirograph
Traces the path of one body relative to another over time, building a Lissajous-like curve
Resonance
Draws a line between two bodies at each moment; accumulates into a string-art pattern whose shape reflects the ratio of their orbital periods
Sky tonight
Shows which objects are visible from a given location on Earth at the current simulation date
Other
R
Surprise me: flies to a random notable object and shows its description
P
Save a screenshot of the current view
?
Show keyboard shortcut reference