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Skyfold Cosmic Odometer

How far you have travelled through space since a date, frame by frame.

Leave blank for today (UTC date).

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Try an example: Since the year 2000, at the equator · Born 17 May 1990 in Utrecht

More about this tool

How it works

From a start date such as your birthday, computes the distance travelled with the Earth’s rotation at your latitude, around the Sun (integrated from VSOP87), around the Milky Way and relative to the cosmic background radiation, with orbits, full Moons and stars whose light left them when you were born.

  • Rotation: circumference of the latitude circle on the WGS84 ellipsoid per sidereal day (86 164.0905 s).
  • Orbit: the Earth’s heliocentric path length, summed from VSOP87 positions every 6 hours (about 940 million km per year).
  • Galaxy: 247 km/s (Reid et al. 2019); cosmic background: 369.82 km/s (Planck 2018). These are separate frames and are not added together.
  • Full Moons: instants of 180° elongation found with the Skyfold Moon theory; light-echo stars: HYG stars brighter than magnitude 6 whose distance in light years is within 3 % of the elapsed years.

Galactic and cosmic speeds carry uncertainties of a few percent; star distances in HYG can be uncertain by 10 % or more for distant stars.

Sources

Part of Skyfold

  • Skyfold Sky & space atlas

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How to use the Skyfold Cosmic Odometer

Find out how far you travelled through space since a date, such as your birthday, with the Earth's spin, its orbit, the Sun's path in the Galaxy and the cosmic background.

What it is for

Sitting still is relative. While you read this, the Earth turns, it circles the Sun, the Sun circles the centre of the Milky Way and the whole Solar System moves relative to the afterglow of the Big Bang. The Cosmic Odometer measures each of those journeys from a start date — usually a birthday — to an end date.

It is meant for curiosity, teaching and birthday cards. Each motion is given with its speed, distance and source, and the motions are listed separately because they are measured against different reference points; adding them up would not mean anything.

Worked example

The second example is someone born in Utrecht on 17 May 1990 at 08:00 (Europe/Amsterdam, latitude 52.09°), counted to 7 November 2026. The summary reads: In 13323 days you travelled about 34.28 billion km around the Sun, 36.48 orbits, with 451 full Moons.

The frame table lists:

Worked example
MotionSpeed (km/s)Distance
Earth rotation at your latitude0.2864329.6 million km
Earth around the Sun29.780434.28 billion km (229 au)
Sun around the centre of the Milky Way247284.3 billion km (0.030 light years)
Solar system relative to the cosmic background radiation369.82425.7 billion km (0.045 light years)

The table of stars whose light left them when you started begins with Arcturus in Boötes (37 light years), Denebola in Leo (36) and Muphrid (37): the light you see from them tonight set off around 1990.

How to read the result

  • Earth rotation depends on latitude: at the equator it is 0.465 km/s, at 52° about 0.29 km/s, at the poles zero.
  • Earth around the Sun is the real path length of the orbit added up from the planetary theory, about 940 million km per year.
  • Galaxy and cosmic background speeds are measured values (247 km/s from Reid and colleagues 2019; 369.82 km/s from Planck 2018) with uncertainties of a few percent.
  • Orbits of the Sun, Earth rotations (sidereal) and Full Moons are counts over the span.
  • The light-echo stars are naked-eye stars whose catalogue distance in light years is within 3 % of your span in years.

Tips and common mistakes

  • Leave the end date empty to count to today.
  • Use the latitude where you lived; it only changes the rotation leg.
  • For a birthday card, round the orbit distance — the figures are honest to a few significant digits, not to the kilometre.
  • Distances to far stars in the HYG catalogue can be uncertain by 10 % or more, so the light-echo list is a fun pointer, not a precise date.
  • Spans of up to 150 years between 1800 and 2150 are supported.

FAQ

Why are the distances not added together?

Each speed is relative to a different reference point — the Earth's axis, the Sun, the Galactic centre, the cosmic background. Combining them needs directions, not just lengths, and the directions keep changing.

Is the orbital distance just 2π × 1 au per year?

No. The tool sums the Earth's actual positions every six hours from the planetary theory, so the elliptical orbit and the timing of your start and end dates are included.

What does "full Moons" count?

The number of instants when the Moon was exactly opposite the Sun during your span, computed with the same Moon theory as Skyfold's ephemeris.

Is my birth date stored?

The tool runs on the date you send and keeps nothing. In the Skyfold app the date stays in your browser and is never put into share links.

Guide last updated:

For scripts and AI agents

  • JSON API: POST https://skyfoldcosmicodometer.usefulweb.app/api/v1/calculate (same calculation as this page)
  • Interface description: OpenAPI 3.1 · AI guide: llms.txt
  • MCP server (Streamable HTTP): https://skyfoldcosmicodometer.usefulweb.app/mcp · tool name skyfold_cosmic_odometer
Example request
curl -s -X POST https://skyfoldcosmicodometer.usefulweb.app/api/v1/calculate \
  -H 'content-type: application/json' \
  -d '{"startDate":"2000-01-01","startTime":"00:00","endDate":"2026-11-07","timeZone":"UTC","latitude":0}'
Feedback · ideas & bug reports welcome