Time and eclipses

The timeline controls a numerical Julian Day internally. The interface accepts a civil UTC date and converts it before sending time to the rendering engine.

Timeline controls

You can:

• enter a UTC date and time;
• play or pause the simulation;
• return to the current date;
• choose a time multiplier appropriate to the current map scale;
• browse documented past and future eclipse events.

When playback is paused, orbital positions and axial rotation remain fixed. When it resumes, both are derived from the same internal time rather than from the render frame count.

Temporal modes

State at selected date displays the estimated state of mapped objects at one common instant. This is the implemented primary mode.

Received light treats the selected date as a reception date. Supported Solar System bodies use an Earth observer and HYG stars use the Solar System barycentre. Each supported object is evaluated at its own emission epoch; a body's axial rotation is evaluated at that same epoch. Object details show the calculated light-travel time and emission date.

The mode currently covers the Sun, Moon, planets, Galilean moons, documented two-body satellites, dwarf planets, asteroids, comets, HYG stars, and exoplanet systems with a published host distance. Astronomy Engine bodies retain a calculated confidence. The remaining Solar System objects iteratively solve their Earth-received delay with the same documented JPL mean or osculating elements used by the map, so that result remains explicitly extrapolated. Visual distance amplification never enters the light-time calculation.

For an exoplanet system, the NASA PSCompPars system distance sets one barycentric delay shared by the host and all its planets, using the IAU parsec definition. The host remains at its static catalogue direction because this layer reconstructs no host proper motion. Each local planet orbit is evaluated at the shared emission epoch, but its phase, orientation, and display scale remain explicitly illustrative rather than an observed ephemeris. Systems without a published distance stay simultaneous.

Nearby galaxies with a catalogue distance now use its geometric light time while their 3D position stays static. Cosmicflows-4 distance moduli are interpreted as luminosity distances; large-scale structure display distances are interpreted as comoving distances. Each is inverted in the same documented flat ΛCDM model (H0=70 km/s/Mpc, Ωm=0.3, ΩΛ=0.7), then the cosmological lookback time is applied. The object card shows the inferred model redshift and identifies which distance type was used. This changes the emission epoch, not the catalogue position or an object's static appearance.

This is a finite-speed-of-light model with a bounded cosmological approximation, not a complete relativistic observation or galaxy-evolution model. HYG uniform-motion extrapolation is bounded to ±10,000 Julian years and is identified when that boundary is reached.

The Earth-observer planetarium remains a separate topocentric projection. It uses the selected observing location for altitude, azimuth, terrain obstruction, and apparent angular size; selecting Received light does not turn the 3D map into that planetarium.

Planetary positions and rotation

Planet, Moon, and Galilean-moon positions are calculated locally with Astronomy Engine. Selected minor bodies and other moons use documented JPL SBDB or JPL mean satellite elements in a simplified two-body provider. The object card identifies the corresponding confidence level.

Supported bodies use date-dependent axial orientation data. Rotation changes with simulation time, including retrograde rotation where applicable. Texture alignment and visible size remain rendering adaptations rather than surface-navigation products.

Eclipse browser

The event browser covers solar and lunar eclipse families relevant to the Earth–Moon system. It can move the simulation to an event, focus the relevant bodies, and calculate local circumstances for either a predefined French observing location or latitude and longitude entered manually. Custom coordinates stay in the browser and use UTC because no geocoding or time-zone service is called.

Solar views can show:

• partial, annular, and total event classification;
• the Moon–Earth–Sun geometry in orbital view;
• the shadow at the selected instant;
• an optional whole-event map whose blue envelope combines partial visibility over time and whose coral or amber band bounds the totality or annularity corridor;
• local contacts C1 (partial begins), C2 (central phase begins), maximum, C3 (central phase ends), and C4 (partial ends), with below-horizon contacts identified explicitly. C2 and C3 only exist for total or annular circumstances at that location.

Lunar views represent the Moon entering the Earth's shadow and distinguish eclipse families in the event list.

Interpretation

The orbital scene exaggerates radii and some separation for readability. Surface overlays are educational reconstructions, not operational visibility forecasts. Always use an authoritative local eclipse service for observation planning and eye-safety guidance.

Contact meanings follow the conventional local-circumstances definitions described by IMCCE. The 12 August 2026 calculation is also checked against NASA GSFC local circumstances for Paris.

Dates outside the documented range

Accuracy depends on the provider and time interval. Long extrapolations, historical reconstructions, and cosmological times are explicitly marked as extrapolated, simulated, or illustrative rather than presented as exact observations.

Next: Scientific confidence.