An introduction to spectroscopy: Applications from astronomy to art

Astronomers have a favorite saying that if a picture is worth a thousand words, then a spectrum is worth a thousand pictures.

A spectrum is measured by the scientific technique known as spectroscopy, and unless you’re already familiar with the term, this may compel you to ask: what is spectroscopy? The short answer is that spectroscopy refers to the study of the interaction between light and matter. Today, the field of spectroscopy is incredibly broad and advanced, with applications in not just astronomy but also chemistry, physics, biology, environmental science, and even art!

The history of spectroscopy goes back to the 17^th century, when Isaac Newton showed that a prism could separate white light into several components that we perceive as colors. The different colors correspond to different wavelengths (and thus energies) of light. In very general terms, a spectrum shows the intensity of each of these wavelengths.

Over the following centuries, scientists developed a range of tools to measure spectra with greater precision. Perhaps most notably, Joseph von Fraunhofer’s invention of the diffraction grating for separating the wavelengths of light was a significant advance over the prism. But it wasn’t until the 20^th century, when quantum mechanics revolutionized the field of spectroscopy, that a myriad of spectroscopic techniques emerged for researchers. One of the most significant tools to be developed for the field of spectroscopy in the mid-20^th century is the laser.

While the term “laser” might bring to mind Star Wars or other popular science fiction, lasers are now ubiquitous in cutting-edge research, and there are several labs on campus at IU that operate different types of lasers. Broadly speaking, lasers enable precise control over several properties of light, including the wavelength, which is incredibly useful for basic science. The applications for lasers in these labs range widely, from atmospheric chemistry in the Stevens Lab, to the study of protein dynamics in the Thielges Lab–something I’ve written about here. In the former case, a laser-based instrument is used to quantify the amounts of volatile organic compounds in the air.  In the latter case, a laser is used to measure an intrinsic property of a biological molecule.

Beyond fundamental research, there’s a role for spectroscopy in the world of art.  Spectroscopy allows art conservators to non-invasively identify the materials used in works of art. The unique chemical signatures detected by Raman and infrared spectroscopy show conservators whether and how their artwork is degrading, thus providing the information needed to preserve old art for future generations to enjoy.

Finally, let’s bring the topic back to astronomy. The instruments used for astronomy today are complex, but they still employ the same phenomenon observed in prisms: a spectrograph splits light from an astronomical body into its many components, generating a spectrum. Astronomical spectra can be analyzed to determine the chemical composition of stars, galaxies, and nebulae, as well as the distance to stars, their temperatures, and sizes. Of course, the excitement of revealing new potentially habitable planets, such as the recent discovery by NASA of seven Earth-sized planets around a single star is also brought to you by spectroscopy!

Astrophysicist Garik Israelian started a TED talk in 2009 with the following claim: “Spectroscopy can probably answer the question: ‘is there anybody out there? Are we alone?’” So in addition to the aforementioned applications, how might spectroscopy answer this compelling question? You can read or listen to the full TED talk here, but I’ll leave you with my own paraphrasing of his statement. Israelian says that the answer to the question “Are we alone?” will come from a spectrum that shows the same molecules in the atmosphere that are essential for life on Earth.

Edited by Maria Tiongco and Clara Boothby