How One Year Spent In Space Translates To Time On Earth

In the vast expanse of the cosmos, the concept of time stretches and twists in ways that defy our earth-bound intuitions. The notion of spending a year in space brings a bundle of questions, chief among them: How does a year in the stars compare to a year on our blue planet? This article embarks on a journey to demystify this intriguing subject, bridging cosmic phenomena with our daily lives and shedding light on the temporal discrepancies between space and Earth through the lens of science.

The relativity of time

Albert Einstein’s theory of relativity plays a pivotal role in understanding how time in space differs from time on Earth. According to this theory, the faster one travels, the slower time passes for them relative to someone stationary. This phenomenon, known as time dilation, means that for astronauts orbiting Earth at high speed in the International Space Station (ISS), time ticks slightly slower than it does for us on the ground.

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Albert Einstein, Credit: Wikimedia/Orren Jack Turner, Princeton, N.J

A year in Space: The Scott Kelly Experiment

One of the most compelling pieces of evidence comes from astronaut Scott Kelly, who spent nearly a year in space while his twin brother, Mark Kelly, remained on Earth. This unique situation provided a rare opportunity to study the effects of space travel on the human body and time perception. Upon Scott’s return, scientists found a very small but measurable difference in the aging process between the twins, underscoring the physical reality of time dilation.

Scott Kelly (NASA astronaut, Ret.) Credit: NASA
Mark Kelly (NASA astronaut, Ret.) Credits: NASA

The mathematical breakdown

The difference, while scientifically significant, is not as dramatic as one might imagine.

 >For example, calculations based on the speed of the ISS suggest that an astronaut would age roughly 0.007 seconds less for every six months in space compared to someone on Earth. For a year, this discrepancy is still less than a second – a tiny fraction undetectable in our daily lives but monumental in physics.

Gravitational influence on time

Beyond velocity, gravity (or the lack thereof) in space also affects time. Einstein’s general relativity explains that the stronger the gravitational pull, the slower the flow of time. Thus, astronauts farther from Earth’s gravity experience time slightly faster than we do on the surface. However, this effect is smaller than that caused by velocity, making the overall difference minuscule to human perception.

The psychological perspective

Apart from the physical effects, the psychological perception of time in space presents another layer of complexity. Astronauts often report a shift in how they perceive time, with days blending into nights without natural light cycles. This subjective experience of time can differ vastly from the objective, mathematical measurements, highlighting the multifaceted nature of time itself.

Long-term implications for space travel

As we set our sights on extended missions, perhaps to Mars or beyond, understanding and managing these temporal discrepancies becomes crucial. The cumulative effects of time dilation could have more pronounced implications on health, and thus, synchronization of space travelers with Earth-bound systems and loved ones seems critical.

The role of technology in timekeeping

To navigate these challenges, space agencies use atomic clocks, which are highly accurate at measuring time. These clocks help synchronize time between space and Earth, ensuring that communication and operations can proceed with precision despite the relativistic effects.

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Atomic Clock, Credit: Wikimedia/Tholme

The future of space exploration

Looking ahead, the continued exploration of space and time offers scientific insights and philosophical reflections on our place in the universe. The nuances of time dilation underscore the interconnectedness of space, time, and gravity – elements that define the very fabric of our universe.

Engaging the public imagination

The conversation about time in space transcends scientific circles, sparking curiosity and wonder among the public. Understanding the basic principles behind time dilation and gravitational effects makes us feel closer to the cosmic ballet that unfolds above us.

Conclusion: A universe of possibilities

While a year in space may be almost identical to a year on Earth regarding raw time, the subtle differences invite us into a deeper appreciation of the universe’s complexities. The journey of astronauts expands our physical horizons and stretches our understanding of time. As we continue to explore the cosmos, we carry with us a sense of wonder and a quest for knowledge that transcends the bounds of our planet. Exploring how time operates differently in space and on Earth broadens our scientific knowledge. It enriches our human experience, reminding us that our perception of time is just a thread in the intricate tapestry of the universe.


How long is space travel?
Space is unimaginably vast; the distance between Earth and Mars is about 140 million miles (140,000,000), and it would take approximately 300 days for you to reach Mars from Earth. Saturn, a farther planet, is about a billion miles from Earth (1,000,000,000), and it would take from 3-6 years to reach Saturn from Earth.
Who has stayed long in space at the International Space Station?
Astronaut Scott Kelly holds the record for the longest single spaceflight at 340 days. For the longest cumulative days in space, astronaut Peggy Whitson holds the record at 665 days.


  • Smore Science Staff
  • Sarita Menon, Ph.D.
    Dr. Sarita Menon is the founder, and Head of Content at Smore Science. With a PhD in cancer research and over 15 years of experience Dr. Menon has honed her skills as a science communicator focused on making complex and important science engaging and understandable to all. Whether reviewing article ideas, working with writers, or editing pieces herself, Dr. Menon’s guiding vision shapes the informative yet captivating content published across both the website and print magazine.

Copyright @smorescience. All rights reserved. Do not copy, cite, publish, or distribute this content without permission.

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