Time in space
Check the space station’s clock, explore Moon and Mars time, then write your own captain’s log.
What time is it on the ISS?
The International Space Station uses Coordinated Universal Time (UTC) to organize its day. It has no daylight-saving clock change.
Enable JavaScript to show the ISS schedule clock and try a fictional stardate. These explanations work offline.
What time is it on the Moon?
You can use an Earth UTC clock while standing on the Moon. But noon-to-noon there takes about 29.5 Earth days—a very long solar day.
Gravity and motion also affect how clocks compare. Scientists are developing a common lunar time reference for navigation and future missions. This is more than choosing a new Earth time zone.
There is no official lunar clock conversion here. BIPM Moon Timing work · NASA’s lunar time project · NASA on the lunar day
Mars has a day called a sol
A Martian solar day averages 24 hours, 39 minutes, 35.244 seconds in Earth units. Rover teams use local Mars time to plan work around sunlight at a particular landing site.
A sol is a day; a planetary year is one orbit around the Sun. Those are different ways of counting time.
How do we measure time in space?
A second is defined using atoms, rather than the turning of a planet. Spacecraft carry clocks, and mission teams choose a reference such as UTC to coordinate events. A mission can also count elapsed days, hours and seconds from a chosen starting event.
When a spacecraft sends a message, the time it happened and the time Earth receives it can be different because light takes time to travel. Gravity and speed also matter when very precise clocks are compared.
US Naval Observatory: atomic seconds and UTC · NASA: time conventions for missions · Try light-travel time →
Captain’s log… what’s my stardate?
Imagine your own Star Trek–inspired adventure. This is our fictional Playground stardate, not an official Star Trek conversion or a scientific space-time standard.
Playground stardate
How long does light take?
Compare journeys from the Moon, the Sun and much farther away.
ExploreCompare two clocks
Explore how constant relative motion changes elapsed time in special relativity.
ExploreA much longer timeline
Travel back through the history of Earth and the universe.
ExploreYour age across space
Try planets, distant star systems and a Sagittarius A* gravity thought experiment.
Explore
A year is a journey around a star
The space age explorer counts the same lived time in each world’s orbital years. Its Sagittarius A* option explores a different idea: a simplified gravity model in which clocks experience less time near a black hole. Every result explains its limits.