In this series, we explore the weird and wonderful world of astronomy jargon! You get the whole picture with today’s topic: Spectrum!
The spectrum of an object is perhaps the most important, useful, and important measurement that can be made in astronomy. The spectrum decodes everything from the composition of this object to its speed. Without the knowledge of spectroscopy, we would be much more confused about the sky than we are.
It was Isaac Newton himself who discovered that the sun’s white light is actually made up of a combination of many different colors – the well-known ROYGBIV of the rainbow. Newton was perhaps the first person to measure the spectrum of our sun. He divided the light of the sun to measure how much of each color was in that light. And that’s essentially a spectrum: a measurement of the amount of each wavelength of light that comes from an object.
In the early days of modern astronomy, prisms were used to separate the light and create a spectrum. Today astronomers use tools like diffraction gratings. But regardless of the technology, the end result is always the same: breaking open a light source to see what’s inside.
A spectrometer – a device that splits light and measures the resulting spectrum – is located on the underside of almost every scientific telescope in the world. One of the many great things about spectra is the amount of information it contains. A single pixel is enough to capture the spectrum, and we can learn something about the object from the spectrum. In fact, some of the greatest discoveries in astronomy have been made in spectra alone.
One of the strongest parts of an object’s spectrum is the appearance of lines. When the object is hot, all elements or molecules emit very specific wavelengths of light that appear as bright lines in the spectrum. If the object blocks another light source, the elements and molecules in the object absorb very specific wavelengths of light, which show up in the spectrum as dark lines or missing gaps.
By looking for these emission or absorption fingerprints in the spectrum, astronomers can determine what the object is made of. This is how we discovered helium in the sun. So we know that the Jupiter cloud tops contain ammonia. So we found amino acids in interstellar gas clouds. This is how we measure the extent of the universe.
Everyone welcomes the spectrum.