Mars Clock | InterImm

Now on Mars

Computed in your browser from your device's clock with NASA's Mars24 algorithm. Nothing is sent anywhere.

Coordinated Mars Time

--:--:--

Mean solar time at the prime meridian (Airy-0), in Mars hours of 1/24 sol.

Mars Sol Date

–

Sols since 29 December 1873, the Mars equivalent of the Julian day.

Season

–

. .

Curiosity

–

Perseverance

–

The Sun from Mars

–

Overhead at , declination .

Earth

–

Local time anywhere on Mars

Pick a landing site or InterImm city, or type a longitude in degrees east.

Place Longitude (°E)

Local mean solar time

–

What a Mars clock set to this longitude reads.

Local true solar time

–

What a sundial reads; 12:00 is when the Sun is highest.

InterImm time ·

–

Earth-length hours, with the extra 39 min 35 s at the end of the sol.

Converter

Earth to Mars, and an InterImm date back to Earth.

Earth → Mars

Earth date and time Entered in

The InterImm date uses the timezone chosen at the top of the page.

The InterImm calendar

24 months named after the Chinese solar terms. Each year starts at the northern spring equinox, and every month starts on a Sunday.

Months 6, 12, 18 and 24 have 27 sols, the rest 28, so a common year has 668 sols. Leap years add a 28th sol to month 24, six years in ten, giving an average of 668.59 sols, close to the 668.5921 of a Mars tropical year. Year 1 began on 28 April 1970.

Timezones

InterImm time uses Earth-length hours, so a sol has 24 hours and 39 min 35 s. That makes 25 zones, each one hour or 14.5987° of longitude wide, counted east from Airy-0.

Zone	Longitude (°E)	Ahead of zone 0	Time now	Places

Put a Mars clock on your site

Pick the options, then copy one snippet. The widget runs in the visitor's browser and costs nothing to host.

Language Timezone Theme

Rover sols Compact

Embed as

Use it in your own project

Everything on this page comes from one small JavaScript file with no dependencies and a test suite. It is free to use (MIT licence) and costs nothing to run: it is served as static files.

In a web page or Node

import { marsTime, interimmTime } from
  'https://cdn.jsdelivr.net/gh/InterImm/mars-clock@gh-pages/lib/marstime.js';

const now = marsTime(new Date(), { longitude: 137.44 });
now.mtc   // Coordinated Mars Time, hours
now.lmst  // local mean solar time at Gale crater
now.ls    // season, degrees
interimmTime(new Date(), { zone: 5 }).clock   // "06:19:12"

As a widget

Use the embed builder above for a styled card, or <mars-clock> for bare text that takes your page's style:

<script type="module" src="https://cdn.jsdelivr.net/gh/InterImm/mars-clock@gh-pages/lib/mars-clock-element.js"></script>
<mars-clock></mars-clock>  <!-- or show="interimm" zone="5", show="sol" mission="perseverance" -->

For AI assistants

Add the Mars time tools to Claude, Cursor or any MCP client. Nothing to install beyond Node:

claude mcp add mars-time -- npx -y github:InterImm/mars-clock#gh-pages

# or in an MCP config file
{ "mcpServers": { "mars-time": { "command": "npx", "args": ["-y", "github:InterImm/mars-clock#gh-pages"] } } }

# or once, from any shell
npx -y github:InterImm/mars-clock#gh-pages now --longitude 137.44

Language models that browse can start from llms.txt; the JSON endpoints are described in OpenAPI.

As JSON, from any language

Precomputed tables, one row per day at 00:00 UTC for 2000–2050, plus Mars Year and InterImm year start dates.

curl https://interimm.org/mars-clock/api/v1/daily/2026.json
curl https://interimm.org/mars-clock/api/v1/mars-years.json

See the index and the README for every function and field.

About

Mars time follows NASA GISS's Mars24 algorithm (Allison & McEwen 2000, Planet. Space Sci. 48, 215–235). The page began as James Tauber's Mars Clock; InterImm added its calendar, timekeeping and timezones in 2016. Source on GitHub.