Yesterday I wrote about how floating helium balloons lead to the idea that everything is made of atoms. Today I want to think about one particular helium atom, an atom in the outer atmosphere of the Sun.
Something strange is about to happen to this atom. As it bounces about at the edge of our star, the helium atom is surrounded by a sea of flying photons. Many photons might pass right through the helium atom, but if the photon is just the right frequency, it plashes into the helium atom and disappears. When light from the Sun reaches the Earth, it will be missing photons of just that frequency. For photons, frequency equals color. Seen through a microscope, the rainbow of light from the Sun will display a dark line where the helium atoms in the Sun’s atomosphere captured those particular photons.
Of course, not only helium creates dark lines in the Sun’s spectrum. In fact, by examining those dark lines in solar rainbows, scientists in the 1800s recognized that all the elements known on Earth present in the Sun, as well. This was an amazing discovery. For thousands of years, the greatest thinkers were convinced that the heavens must be made of different stuff than the dirty, imperfect Earth. But scientists, by examining the tiny black lines in solar rainbows, found a deep connection between the heavens and ourselves.
And yet the fit wasn’t perfect. There were extra lines in the Sun’s spectrum. These lines didn’t match any known element, and so the scientists conjured a new element, unknown on the Earth. They named it after the Greek god of the Sun, Helios the charioteer. Were, in fact, the heavens different from the Earth?
No! Decades later, a scientist named William Ramsay discovered an unknown element, a gas that was often found in association with the mysterious element uranium. When Ramsay isolated this light, non-reactive gas, he found that its spectrum matched the Sun element. Helium, as with all the other elements, wasn’t found only in the heavens, but on the Earth, as well. We and the stars were one.