An Ephemeris of Distance — live
Being a table of ranges and light-time

Computed for the present moment

Select any two bodies of the solar system. Their separation and the time light requires to cross it are reckoned afresh, as an almanac reckons the rising of stars.

Reckoning what lies nearest…

The distance from
to
at this hour —
·
Separation, centre to centre
— km
—
Time for light to cross
—
A signal returned would take —
Rate of separation, this instant
—
Reckoned from the change in range over the coming day — bodies on eccentric or fast-shifting paths may show a momentary figure rather than a steady one.

Looking ahead, one year

The same two bodies, their range traced forward three hundred and sixty-five days from today.
Nearest approach in the year ahead
—
—
Farthest range in the year ahead
—
—
Doppler shift on a carrier of MHz
—
As reckoned from the rate of separation alone — a first approximation, ignoring the motion of the receiving station.
Synodic period — the cycle of returning alignments
—
Applies to two bodies that each circle the Sun directly.
Apparent disc, seen from the first body
—
—

Were you to travel there

The same range, set against the pace of various known conveyances — a straight-line division of distance by speed, not a real trajectory. No acceleration, no coasting, no gravity assists, and no allowance for air or vacuum are reckoned here; actual missions take longer and follow curved paths. Treat these as a sense of scale, not a flight plan.
BySpeedTime required

Routed by way of a third body

A signal need not travel direct — here it is relayed through an intermediate body, received and resent.
Relay via
Total light-time by this route, against the direct path
—
—
Surface gravity—
Escape velocity—
—
Surface gravity—
Escape velocity—

Travel through time

Slide the range to reckon the separation at any moment within two years either side of today. The orrery and all figures above move with it.
now
Hohmann transfer — minimum-energy orbit
Gravity-assist Δv budget

Your weight, worlds compared

Surface weight of a given mass on every body in this catalogue.
A mass of weighs —

Notable events — next two years

Local minima and maxima of the separation — conjunctions, oppositions, and greatest elongations — scanned forward 730 days.

Launch windows — Hohmann opportunities

Each window is a moment when departing on a Hohmann transfer arc will place you near the destination at arrival. The Δv figures are computed from mean orbital radii and are therefore constant per body pair — a real porkchop plot would show per-window variation. Only meaningful for two planets.

Where the interstellar probes are now

Three craft now beyond the planets, reckoned from their last known heliocentric range and outward speed — distance from Earth is approximated as distance from the Sun, accurate to within about one astronomical unit.
Figures update each second from a linear projection anchored to NASA/JPL tracking data; treat them as close estimates, not live telemetry.

Artificial satellites, tracked live

Real orbital elements, fetched fresh from CelesTrak and propagated by SGP4 — the standard model used to track everything humanity has placed in Earth orbit. Pick a category, then a satellite within it; its position is recomputed continuously in this page thereafter, without a further fetch.
Category satellite
fetching elements…
Elements drawn directly from CelesTrak (ultimately sourced from the 18th Space Defense Squadron) — last fetched —. All propagation thereafter happens here in your browser, not on a server. If this panel cannot reach celestrak.org, your network may be blocking it.

The full table

Sun and the eight planets, in millions of kilometres. Touch any figure to set it above.