Twinkle, twinkle little star …

… how I wonder what you are! If you spoke English as a child, you probably remember singing that. Did you really look at the stars and wonder? If you have a child or grandchild, take them outside on a dark clear evening. In early December the moon will not be up, which helps. Sing the song together — that child may grow up to be an astronomer and understand the stars. The wonder will still be there.

Sadly, the Chicagoland sky is never dark enough to just look up and see a thousand stars, as I could as a child in the English countryside.

For all antiquity nobody knew what stars were. When Copernicus realized that the sun, not Earth, is the center of the universe, the stars were placed on a far distant giant sphere. Some thought they might be holes through which shone the light of heaven. Copernicus, who was nineteen when Columbus first sailed across the Atlantic, started the Scientific Revolution, followed by Galileo and Newton, and the Age of Discovery began.

This shows sunlight spread into its spectrum of colors, like a rainbow, with a pattern of dark lines called Fraunhofer lines, since he first catalogued them. They are due to atoms absorbing light of very specific wavelengths. Every element has its unique pattern of lines, like a barcode. Read that, and you know the composition of the outer layers of the sun — and the stars too! Image

Galileo looked through his little telescope at the night sky and saw thousands more stars. Even in a powerful telescope they are tiny points of light, so how can we know what they are, how they work?

Newton used a glass prism to spread sunlight into a “rainbow” of colors. Only in 1802 did the English scientist Wollaston notice some dark lines in that rainbow. In 1814 Fraunhofer replaced the prism with a diffraction grating (try with a CD) and tabulated hundreds of those lines. Later it was found that hot gases emit bright lines at the same wavelengths (colors) and each element (hydrogen and sodium, for example) has its own pattern of lines. Nobody knew why until the structure of atoms was understood.

Like an item at the supermarket checkout, every star has a barcode. Read that barcode and you know its composition! If light were sound, each element would be singing its own chord.

With bigger telescopes and long-exposure photography, the barcodes of stars could be measured by the thousands. Imagine! Able to study the elements in the stars! That was just the start. Those lines shift to the red if the star rushes away, so we discovered the expansion of the universe and how galaxies rotate. Applying physics, we now understand even the centers of stars and how they shine. Knowing that makes them even more wonderful.

This is a version of an article that original appeared in Positively Naperville.