# Skyfold Cosmic Odometer

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

Part of usefulweb.app (https://usefulweb.app/). Part of [Skyfold](https://skyfold.usefulweb.app/) (ownerApp: skyfold). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://skyfoldcosmicodometer.usefulweb.app/ (interactive tool at https://skyfoldcosmicodometer.usefulweb.app/tool)
- JSON API: POST https://skyfoldcosmicodometer.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://skyfoldcosmicodometer.usefulweb.app/api/v1/tool)
- OpenAPI: https://skyfoldcosmicodometer.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://skyfoldcosmicodometer.usefulweb.app/mcp - tool `skyfold_cosmic_odometer`

## Inputs
- startDate (date): Start date (for example your birthday)
- startTime (time): Start time
- endDate (date): End date - Leave blank for today (UTC date).
- timeZone (text): Time zone
- latitude (number): Latitude for Earth’s rotation

## Method
- 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.

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