How do astronauts tell the time in space?

Do you set your time-keeping devices by sunrise and sunset?

The same way people on Earth do – by watches and clocks.

@Zaku Day light savings time and time zones. We still do. Is Earth centered time keeping. In outer space and beyond won’t be very usefull.

@Darth_Algar Which time zone do they use? Houston or other. Would be meaningless when we go beyond the Earth.

They use Coordinated Universal Time (UTC). That’s pretty much the defacto time zone used by most of the world’s scientific institutions.

We’re really more interested in intervals than in some absolute time designation most of the time. Any device that measures intervals ought to do, as long as it doesn’t depend on Earth’s gravity. So no hourglasses. No sundials, either.

They don’t tell, in space no-one can hear you tell, they just look.

If a government time signal can reach across the United States, it can extend to space. But any simple drug store digital watch would suffice.

Just as we do here on the ground, they can operate on “local” time. Astronauts can choose to match their clocks to those of mission control back home, but their clocks will drift over time from any earthly counterpart due to the relativistic effects accompanying space travel velocities. From our point of view here on earth, space travelers’ clocks run slower than ours.

It’s completely arbitrary – as it is on the surface of the planet.

People on Earth used to basically tell time by where the sun is in the sky, especially high noon.
When railroads came along and needed to keep schedules, the meaning of a specific time had to be synced up from one place to the next, and time ‘zones’ were created. By that time telegraph had also been invented so there was a way to communicate in ‘realtime’ a specific synchronizing moment like midnight or noon so the clocks could be set alike.

Star Trek addressed the question with “Star Date” which was simply synced with an agreed standard probably based on Earth time at Star Fleet headquarters. They conveniently seemed to have adopted Earth hours, too….

Pretty much how most science fiction goes. There might be localized time, but the galaxy (or whatnot) at large almost always seems to run on some standardized galactic time.

Nasa sends via communication signals ( computerized).
I suppose it would be like a person stranded on an island?
They would begin by marking the days from when they landed .
In ancient days they never marked hours as in the present, but rather they marked Seasons to know when to harvest there crops.