Zero Gravity Day (Mujūryoku no Hi)

What is Zero Gravity Day?

June 16th is "Zero Gravity Day" every year. It comes from the wordplay "mu (6) - jū (10) - ryoku (6)" — a phonetic match for "mujūryoku," meaning "zero gravity" or "weightlessness." The day was established in March 1991 by the town of Kamisunagawa, Hokkaido, which was home to the Japan Microgravity Center (JAMIC), an underground zero-gravity research facility. It's a day to learn about the possibilities that weightless (microgravity) environments — like those found in space — offer for scientific research and industry, and to nurture curiosity about uncharted frontiers.

A Zero-Gravity Facility in a Coal Mining Town

A small coal mining town in Hokkaido was once home to a rare hub for microgravity experiments.

• Built on a former mine shaft: Opened in 1991, the facility repurposed a vertical shaft more than 700 meters deep at the closed Mitsui Sunagawa coal mine. By dropping a capsule down the shaft, it could create about 10 seconds of weightlessness on the ground — said to be the longest in the world at the time.
• Used for many kinds of research: The facility was used for experiments such as developing new materials and studying combustion, and researchers from overseas also used it. It closed in 2003, but the headframe tower over its central shaft still stands.

Curious Phenomena in Microgravity

In an environment almost free of gravity's effects, things behave differently than on Earth.

• No "convection": On Earth, warm air and liquids rise while cooler ones sink, creating "convection." In weightlessness this convection almost disappears, which is useful for research on mixing materials evenly and growing high-quality crystals.
• Flames become round: A candle flame on Earth is stretched upward because heated air rises. In weightlessness there is no rising air current, so the flame becomes round.

Interesting facts about weightlessness

• Not "zero G" but "microgravity": Even inside experimental facilities or a space station, slight accelerations and vibrations remain, which is why specialists call it "microgravity."
• Growing taller in space: In space, the discs between the vertebrae expand once freed from gravity, so astronauts can become several centimeters taller. Their height returns to normal back on Earth.
• Water becomes a ball: Without gravity, liquids pull themselves into spheres through surface tension. That's why water floats as round balls aboard a space station.
• Three ways to create weightlessness: The main methods are drop towers or shafts, "parabolic flights" in which an airplane flies along an arc, and orbiting spacecraft such as the International Space Station (ISS).
• Space sickness: In weightlessness, signals from the balance organs in the inner ear can conflict with what the eyes see, which is thought to cause "space sickness."

Tips for Zero Gravity Day

• Watch a space documentary or science fiction film and imagine a world without gravity.
• Look up experiments on the International Space Station and the work of Japanese astronauts.
• Check the latest news on the space business and space tourism.
• Ask family or coworkers what they would like to try if they were weightless.

Looking Again at Everyday "Gravity" Makes the World Look a Little Different

June 16th is a day to think about gravity, something we rarely notice. In a coal mining town in Hokkaido, a deep underground shaft was once used to create weightlessness for research connected to space. We can stand, walk, and hold things only because of gravity. Today, why not look up at the sky and spend a moment wondering about space and gravity?