Emulating Earth’s light-dark cycle is important for astronaut health and safety

Astronauts follow strict schedules to mimic Earth days and stay healthy in space

Experiencing 15 sunrises and sunsets a day while aboard the International Space Station, visitors preserve their circadian rhythms and mental health with fixed timetables. Astronauts have described sleep as living in a vacuum cleaner due to ongoing air filtration.

Astronauts exercise on the International Space Station

Astronauts maintain bone, muscle, and cardiovascular health with physical activity. It's crucial astronauts make time to exercise for approximately two hours per day. This resource offers a behind-the-scenes look at how high-intensity workouts help prevent muscle atrophy, bone density loss, and aerobic decline during months-long space missions.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

There is a template for how to live a better, healthier day, and it includes a digital sunset

Science suggests that early-morning exercise, later-morning peak work or social time, consistent exercise, and a "digital sunset"—starting to turn down the lights in the evening and avoid screens—are important for circadian health.

Watch how dozens of everyday human tasks are performed in space

This playlist features clips of astronauts aboard the International Space Station explaining how they cook, eat, sleep, and conduct research in microgravity. Other activities to pass the time, including watering plants and playing soccer, are also shown.

Artificial lighting and modern practices like working late are linked with sleep shifts

An analysis of five adults participating in a German reality program that tasked them with living in a Stone-Age-like settlement for 2.5 months, provided some insights into how modern conditions may have shifted our circadian rhythms. The participants slept about 90 minutes more under these conditions, and went to bed earlier and rose earlier, raising questions about how circadian rhythms, sleep, and sleep quality are affected by modern lifestyles.

Lack of sunlight during Arctic winters can fuel a winter slump and a circadian disconnect

Sunlight typically tells our brain to stop producing melatonin, a hormone that makes us sleepy, but in dark Arctic winters humans must adapt to life without much sunlight. Scientists in this video provide tips that include trying to increase the amount of light around you, even if it’s just table lamps.

Protecting astronauts against space radiation

Outside the protective atmosphere of Earth, astronauts are constantly bombarded by radiation, which, among other dangers, increases the risk cancer. While those of us on Earth can mitigate the effects of similar radiation by limiting exposure,...

Temperature and certain medications can also affect your circadian rhythms

Although light and dark have the largest influence on circadian rhythms, temperature, stress, and certain medications are among the factors that also play a role. Persistent trouble sleeping or staying asleep may signal it’s time to see your doctor to get a better sleep-wake schedule.

Chronobiologists study the effect of time on biological cycles

Circadian rhythms were first observed in the 1700s, when French astronomer Jean-Jacques D'Ortous de Mairan put a plant in a dark room and watched it still respond to day and night cycles, setting off further studies about specific light-dark biological cycles, an area of inquiry that continues today with the human "clock proteins" at the molecular level.

Watch a livestream of Earth from the International Space Station

The feed is made possible by the SpaceTV-1 camera system, which is live over 20 hours a day. Video replays are shown during routine loss of signal communications with the inter-satellite link relaying the video data.

Light pollution is giving oysters insomnia

Oysters, bivalve mollusks that have light-detecting cells along their skin, can't sleep with all this artificial light. According to a 2022 study, oysters' sleep cycles are disturbed by light dimmer than that provided by the full moon. As with humans, it's possible that these bouts of insomnia could have adverse health effects and contribute to the development of disease over time.

Olympians view sleep as a performance tool, prioritizing routine and environment

Elite athletes emphasize consistent sleep routines, dark and cool environments, the well-placed nap, and tools like eye masks, white noise machines, and supplements like melatonin (particularly for jet lag). This priority belies a core principle: recovery and performance are inseparable. Read more ways Olympians "sleepmaxx" here.

Ending daylight saving time may prevent as many as 300,000 strokes annually

Changing clocks twice a year disrupts circadian rhythms, which last an average of 24 hours and 12 minutes. Studies have shown that permanent daylight saving time provides fewer health benefits than standard time.

The crew of Artemis II captured a photograph of Earth setting as they orbited the moon

On April 6, 2026, the Artemis II astronauts captured a striking image of Earth setting as their spacecraft orbited the Moon, echoing the iconic Earthrise photo taken by Apollo 8's Bill Anders 58 years earlier.

The International Space Station is slowly falling due to atmospheric drag

To stay in orbit, the largest human-made object in space needs periodic rocket boosts to maintain its orbital speed and height. Its solar panels collect enough energy to power over 60 average US homes each year.

NASA uses extreme Earth environments to prepare for space exploration

Analog missions in volcanic terrains and craters mimic Martian and lunar environments. Crew members operating in these missions, including at sites in Utah, Nevada, Arizona, and Hawai'i, test suits and specialized space instruments under simulated conditions.

In 2013, an astronaut's helmet began filling with water during a spacewalk

A leak in the cooling system of Luca Parmitano's spacesuit caused water to obscure his vision and silence his radio as the International Space Station entered Earth's shadow, forcing him to feel his way back to the airlock in darkness.

Studying the circadian clock of a tiny swimming polar creature may help forecast polar ecosystem health

A 2025 study found that Antarctic krill, a food chain staple in the Southern Ocean, have an internal biological clock that helps regulate its swimming patterns and helps the tiny shrimp-like animals adapt to daily and seasonal environmental changes. Better understanding of how the clock and light cues interact may help scientists understand how well the species will respond to pronounced climate change in the polar region.

The REM cycle happens around four to six times per night

Sleep is a natural process that is critical to maintaining life—a process conserved throughout evolution across just about any animal with a brain. Generally speaking, the first three stages involve increasingly deep phases of non-REM sleep, followed by a roughly 90-minute period of REM sleep that repeats throughout the night.

The team responsible for the first interplanetary sundials included Bill Nye

While reviewing designs for instruments to be carried by future Mars rovers, Nye suggested adapting the function of a calibration tool, which would be used by the Spirit and Opportunity rovers to help calibrate the brightness and color of their panoramic cameras on the Martian surface.

Changes in Earth's orbital cycles influence the timing of ice ages

These cycles include changes in Earth's orbit shape, tilt, and wobble, all of which alter how much solar energy different parts of Earth receive over time. Due to orbital eccentricity, summers in the Northern Hemisphere last about 4.5 days longer than winters.

The Polaris Dawn program led to the first commercial spacewalk

As part of the Polaris program, this first mission included a crew comprising astronauts and SpaceX engineers, who conducted scientific experiments and cultural outreach, such as raising funds for St. Jude Children's Research Hospital.

Explore the Earth at night from space

See the planet in all its luminosity with this NightEarth app, an interactive spherical globe showing real satellite imagery of Earth. Toggle between views of real-time clouds, aurora borealis activity, and more.

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

Why time ticks faster on the moon, which may need its own time zone

Because Earth exerts a stronger gravitational pull than the moon, it lags behind between 56 and 59 microseconds each day, or about one second every 46.5 years. This impacts essential synchronous operations of future electronic equipment on the lunar surface, which could be alleviated by a standardized conversion system between Earth and moon time zones.

Astronauts have repaired genetic damage in space using CRISPR—a molecular tool that can make precise changes to DNA and is used in single-celled organisms to attack invasive viruses.

In 2024, China announced plans to establish an international lunar research station

The strategy, which runs until 2050, focuses on advancing space science, fostering technological innovation, and exploring habitable planets and extraterrestrial life, beginning with landing astronauts on the moon before 2030.

Stars appear to twinkle because turbulence in the motion of molecules in Earth's atmosphere causes light to bend and wiggle rapidly on its way to the surface—a phenomenon called scintillation.

Before humans, the Soviet Union and the United States sent animals—including apes, dogs, and cats—to space during the Space Race.

Explore the known asteroids, comets, and spacecraft involved in asteroid studies within our solar system with 'Eyes on Asteroids,' a 3D visualization from NASA.

Apollo astronauts left items in the moon's 'toss zone,' including golf balls, family photos, and bags of human waste, to make room for lunar rocks.

After NASA's Voyager 1 captured Earth as a single pixel as it left the solar system in 1990, astronomer Carl Sagan used the image to reflect on humanity's fragility and the responsibility to protect 'the only world we've ever known.'

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Fish populations in the Great Barrier Reef have increased after installing waterproof speakers on the ocean floor that played recordings of sounds from healthy coral reefs.

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.

Children are now three times more likely to say they want to be a YouTuber when they grow up than an astronaut, with some even attending 'YouTube camps' that teach kids how to create content for the platform.

About 12.5% of US adults experience a phobia in their lifetime, a diagnosis that hinges on the intense fear interfering with daily life and persisting for at least six months.

Watch the cumbersome, but necessary, precautions healthcare workers must take to care for and protect themselves while caring for Ebola patients.

Telehealth demand for GLP-1s for weight loss is booming as consumers seek easier access.

After the Boston Tea Party, colonists switched to coffee, which became the main morning drink for revolutionaries.

Electrical grids worldwide must double their power delivery capacity by 2050 to meet surging demand from AI and electric vehicles.

NBA superstar Victor Wembanyama spent the 2025 summer training with monks in central China to enhance his body and mind.

The distributor behind 'Rocky Horror' pulled the film from its scheduled national release, believing it would be a failure, though it eventually amassed a dedicated fanbase through midnight showings, a trend that continues over 50 years later.

An initial public offering or 'IPO' is the process of a private company becoming public by putting shares of the company on the stock market for purchase.

Take a 3D tour of the Hajj, Islam's annual pilgrimage to Mecca, undertaken by over 1.5 million Muslims.