Mini Object Lesson: Our Reactor in the Sky

Editor’s Note: This article previously appeared in a different format as part of The Atlantic’s Notes section, retired in 2021.

The Monday after Daylight Savings Time starts is a drag. Students nod off in morning classes while bleary-eyed teachers clutch mugs of coffee, desperate for caffeine to replace an hour of lost sleep. It’s a day of dramatic proclamations about the uselessness of time and the futility of aligning clocks with sunlight.

As the hours trudge forth, however, the moaners hush. The frustration of lost sleep gives way to the luminous pleasure of a lengthening day. Sunlight extends past dinnertime. Dog walkers, soccer players, and children in playgrounds bask in a later twilight. Though humans organize our schedules around the clock, Daylight Savings reminds us that our lives, like our planet, revolve around the sun.

The sun is a nuclear reactor. For more than four and a half billion years, its dense gravity has been pulling hydrogen atoms towards its core where they collide and join, their nuclei merging to form helium and other elements. This process, nuclear fusion, releases tremendous energy, which rises out from the core towards the photosphere, the lowest layer of the sun’s atmosphere.

In just over eight minutes, the length of time it takes to hard-boil an egg, solar energy, in the form of electromagnetic waves, travels from the surface of the sun to Earth. Depending on their size and frequency, these waves cause unique effects. Longer infrared waves heat our planet. Medium waves create sunlight, (the only visible evidence of solar radiation). The shortest waves, invisible to the human eye, are ultraviolet light.

These three types of waves are responsible for all the energy on Earth. Plants use photosynthesis to convert light energy into chemical energy. This energy is dispersed when creatures nibble on leaves. Later, when plants and animals die, their stored energy becomes soil, which, through geologic accumulation and pressure, transform into fossil fuels such as oil or gas.

Recently, physicists in Germany and China have been racing to produce temperatures hotter than the sun in order to create and maintain hydrogen plasma, a critical ingredient for nuclear fusion. Their goal? For nuclear fusion to become viable sources of electrical power on Earth. While German physicists have created the hottest temperatures, reaching upwards of 80 million Kelvins (more than five times the estimated heat of the sun’s core), scientists at the Institute of Physical Science in Hefei have sustained hydrogen plasma for longer, clocking out at 102 seconds.

Both achievements are remarkable, but humans don’t have to recreate the sun in order to harness its power. After all, as Daylight Savings annually reminds us, the Earth and its inhabitants already make terrific use of the reactor in our sky.

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