Light: It’s More than We Think

Flip a switch. Turn a knob. Push a button. Look in the sky in the day or at night. Each of these actions will allow you to see light, and most people see light as nothing more than an illuminator. Its purpose in the field of astronomy is much more than illuminating the Universe for us to see. Light is the most significant means of measuring just about everything out there. One specific application is figuring out the composition of objects we are looking at.

This is done through spectroscopy, or getting information from spectra, pictured above. An emission spectrum is obtained when a hot, low-density cloud is shone through a prism. Conversely, an absorption spectrum is obtained when a hot light source is shone through a cooler gaseous cloud through a prism. Analyzing the spectra, we see colored lines on a black background or black lines on a continuous spectrum. What does this tell us?

The presence/absence of colors represent a “fingerprint” of an element. In the picture shown, the spectra represent the “fingerprint” of hydrogen. It may seem simple for us then to analyze the composition of objects in the Universe, but the trick comes when objects are made of multiple elements. The spectra would have colored/black lines all over and we’d have to decipher it. Luckily, computer programs aid in this endeavor but nonetheless, it is an application of using light as measurement.

So next time you flip a switch or look at the stars at night, you can think about what elements are present to emit the light you’re seeing. Impossible is the task of knowing, but interesting enough to wonder about.