The middle of the Sun, the Earth and the universe


What would you find at the exact center of our world? the Sun? the Universe?

Anyone with a below-ground basement or who visits a cavern knows that just a few feet down, the thermometer barely changes year-round. That’s also the temperature of the water that your home’s submersible pump delivers to you. Around here, that’s 52 degrees Fahrenheit, give or take a couple of degrees. Caves thus give the impression that our planet’s interior is chilly.

But volcanoes and hot springs argue otherwise. These days, deep mines provide answers. After the consistent cool rocks of the first few dozen feet, temperatures start to climb and continue upward by one degree for every 100 to 200 feet of depth. Today’s deepest working shaft – a gold mine in South Africa 12,500 feet below the surface – roasts at 131 degrees Fahrenheit. Experimental borings have gone even farther, to nearly 40,000 feet. That’s still just 1/500th of the way to the Earth’s center, which holds surprises even if it isn’t sweet and crunchy.

In 2005, researchers confirmed that Earth’s inner core – a solid ball the size of Pluto – rotates faster than the rest of the world, as if there’s a planet within our planet. Could there be an empty chamber there, where a person would feel weightless? Gravity is indeed zero at Earth’s center. But “floating” wouldn’t be the sensation that you’d get. Our innermost core suffers the pressure of 4,000 miles of metal and rock crushing down from all directions. Let’s not go there.

Earth’s liquid metal core, swishing around that innermost solid iron core, is electrically conductive and creates our global magnetic field. This is a good item, because it deflects high-speed solar and cosmic particles. Some of the bad stuff leaks through anyway, yielding a steady rate of biological mutations that continually alter Earth’s zoo-parade of animals. But most radiation is blocked. By comparison, look next door: The Martian core froze up, destroying its magnetosphere: one reason land is so cheap there.

The Earth’s center bubbles at a fierce 8,500 degrees Fahrenheit thanks mostly to the decay of radioactive elements like uranium and thorium. Standing barefoot, you feel a bit of this heat percolating from below. But it’s overwhelmed: We surface creatures feel 5,000 times more warmth from the Sun above than from the ground below. On other worlds, the story is reversed. Jupiter and Saturn’s gaseous surfaces get twice as much heat from their own interiors than they do from the Sun.

Since life needs energy, we must take seriously that creatures might live “down below” on various moons or planets. Seemingly lifeless worlds might teem with underground biology. Indeed, the standard sci-fi image of aliens in surface cities may be as wrong as it is unimaginative.

In stars, nucleosynthesis happens deep below, too. The Sun’s gaseous surface is merely where we view its energy release. The surface that we see isn’t remotely hot enough for fusion. Those emerging solar photons of friendly visible light started out as brutal gamma rays deep inside, whose photons stretched like taffy during countless encounters along their million-year journey to the surface.

All that nice solar heat and light began in a tiny sphere just 1/200th the volume of the Sun. This minuscule ball at the Sun’s exact center produces 96 billion H-bombs of energy each and every second.

So much for the center of the Earth and the center of the Sun. What about the center of the universe?

Even though we usually visualize the cosmos to be an enormous ball, that’s not accurate for a couple of reasons. First, it may be infinite in spatial extent, and an infinite entity has no shape. (For that matter, neither does an infinite entity have any physical meaning.) Second, to picture the cosmos as a ball, you must be contemplating it from an exterior perspective. There’s no such viewpoint, since by definition nothing is outside the universe. But most importantly, no matter which galaxy cluster you live in, you view all others racing away from you, which is one reason we know that the center of the universe is actually occupied by you, the observer.

You constitute the center of the universe. And this remains true no matter how you define yourself. Glad we could clear this all up.


Want to know more? To read Bob’s previous “Night Sky” columns, visit our Almanac Weekly website at

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