• Choose a category
• All
• Classic-Fiction

By Root 469 0

lab burner) at last revealed the meaning behind these bright and dark lines. With the clear hot flame of Bunsen's improved instrument, free of the deceptive contamination that plagued earlier researchers, the two German colleagues were able to conclusively prove that each chemical element produces a characteristic pattern of colored lines when heated and viewed through a spectroscope. The elements weren't emitting an entire rainbow but rather just a few select colors. More consequential, the patterns were as unique and distinguishing as a fingerprint. Each element on the periodic table had its own personal set of emissions. Using their spectroscope one evening to peer at a distant fire in the port city of Mannheim, visible across the Rhine plain from their laboratory window, Kirchhoff and Bunsen were thrilled to detect the spectral signatures of barium and strontium in the roaring blaze. It didn't take long for them to fathom that they could analyze the Sun and stars in a similar fashion, as light knows no distance in the voids of space. Light can be sent through a spectroscope whether it originates from a distance of one foot, ten miles, or a billion light-years away. Before this revelation, astronomers only knew that a star shines, that it occupies a certain position on the celestial sphere, and in some cases moves. But now they were acquiring the means to determine a star's composition and temperature, information once thought impossible to glean.

When an element is hot and glowing, it radiates its distinctive pattern of spectral colors. But at other times it can absorb those same wavelengths, which explains the origin of the dark lines that Fraunhofer found in the solar spectrum. Each element in the Sun's cooler outer atmosphere absorbs its designated colors, robbing the sunshine of those selected wavelengths before they arrive on Earth. The bright lines are simply the reverse of this process—the elements emitting those very same wavelengths of light as they fiercely burn. Either way—dark or bright—the pattern of lines indicates the presence of the element. Not until the early twentieth century, with the advent of atomic physics, did scientists come to understand this behavior as arising from the electrons in an atom jumping from one energy level to another, the atoms emitting bursts of light when they lose energy and gaining energy when they absorb the photons.

Astronomers quickly realized that, along with revealing a star's composition, a stellar spectrum could also tell them how the star was moving. In the 1840s the Austrian physicist Christian Doppler had surmised that the frequency of a wave, such as the tone of a sound wave or the color of a light wave, would be altered whenever the source of the wave moved. We've all heard the pitch of a siren rise to a higher tone as a police car or ambulance races toward us. This is the very effect that Doppler spoke of: The sound waves emitted by the screeching siren crowd together as they approach us, shortening their length and likewise raising the pitch. Conversely, as the police car pulls away, the sound waves stretch out, producing a lower pitch. In an analogous fashion, a light wave's length is shortened (gets “bluer”) when the source of the light approaches and is lengthened (gets “redder”) when the source moves away.

Astronomers, though, don't assess the overall color of a star or galaxy to measure its speed. That would be too difficult. They can more easily examine how the bright and dark lines in a celestial spectrum shift from their well-known laboratory positions. Depending on the object's motion, the lines can shift toward either the blue or red end of the spectrum. If a star or nebula, for example, is headed for us, its spectral lines move over toward the blue—that is, the lines get “blueshifted.” If moving away, the lines swing over toward the red and hence become “red-shifted.” The exact velocity is pegged from the amount of shift in the spectral bands. Blueshifts and redshifts are nothing less than the speedometers of the universe.

Keeler had the eye of