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Group Captain Shubhanshu Shukla of the Indian Air Force is currently at the International Space Station. He and three other astronauts have traveled to space for 14 days under the Axiom 4 mission. This is a private mission operated by Axiom Space. There are many questions about Shubhanshu's space mission—how do they keep track of day and night on the space station, how many hours are there in a day, and which time zone is followed in space?
On Earth, there is one sunrise and one sunset in a 24-hour day. But on the International Space Station, there are 16 sunrises and 16 sunsets within 24 hours. Based on this, there is a 90-minute day and a 90-minute night on the ISS, while on Earth, day and night typically last about 12 hours each. This is because the space station orbits Earth at a very high speed, taking only 90 minutes to complete one orbit.
During each orbit, the space station remains in sunlight for about 45 minutes, and in Earth’s shadow for the remaining 45 minutes. Since it completes 16 such orbits in 24 hours, the astronauts witness 16 sunrises and 16 sunsets each day.
As for the time zone, the station follows the Coordinated Universal Time (UTC) to maintain consistency with different countries around the world. This time zone is also known as Greenwich Mean Time (GMT).
Astronauts from several countries work together on the ISS, and each country has its own time zone. The use of UTC helps align all mission control centers and astronauts under a single system. This not only makes communication easier but also helps in issuing commands smoothly. Astronauts from countries like the USA, Russia, UK, and Japan operate under this universal time zone in space.
If it is 12:02 PM IST (Indian Standard Time) on 30 June 2025 in India, and considering that IST is 5 hours 30 minutes ahead of UTC, then the time on the International Space Station would be 6:32 AM UTC. This is the standard time used by all space missions, astronauts, and mission control centers.
Specially designed watches and devices are used to calculate time on the ISS. Time is tracked using computers and digital clocks, which are set according to the UTC time zone. In addition, digital displays are installed showing the time of various mission control centers, all synchronized with UTC.
The ISS also uses atomic watches, which are extremely accurate and are crucial for scientific research in space. However, these are mainly used for research purposes and not for daily activities. The time on the ISS is also synchronized with Earth's mission control centers via radio signals.
Astronauts wear digital watches specially designed to function in the microgravity and vacuum of space. For instance, NASA used the “Moonwatch” during the Apollo missions, which could operate in the harsh conditions of space. While time is primarily tracked using digital systems on the ISS, some astronauts also use such personal watches.