When one discusses black holes (as we had done last time) it becomes almost inevitable that one lands upon the topic of light. After all, the commonly held belief is that “Hey! Light can’t escape black holes! Isn’t that cool?

And more than the fact that black holes capture light altogether, black holeswell, any bodies with strong gravity, for that mattertend to have funny effects on light. But all of that is to come…

Before we begin discussing the multi-faceted, fascinating complexities of light, a proper understanding of what light is must first be achieved. And for that, we must travel down the lanes of history and memory, back to the annals of time…

Scientists have been studyingand have been fascinatedby the phenomena of light since the start of science. It was this mysterious property; no one really understood what it was, how it worked, or, for that matter, any of the necessary facts that need to be achieved before one achieves an understanding of an object.

The first breakthroughs regarding light were achieved in the 19th century by Thomas Young. I won’t bore you with all the details of his experiment as the implications of the experiment are much more interesting; it was proved that light demonstrated signs of constructive interferenceor two waves combining to make one big wave—to create bright spots and signs of destructive interferenceor two waves canceling each other out—to create areas of darkness.

When Young realized that light was following so many properties of waves, he realized that he had proven that light, in fact, behaved like a wave! But, as is consistent with several of the “great discoveries of science”, a small problem was unearthed with this conclusion.

You see, scientists had understood, by then, that a wave needs a medium to travel in. For example, sound waves can travel through air and water and metal (substances that enable the wave to hop from particle to particle).

But, as is immortalized by the ominous tagline of the movie Alien, “In space, no one can hear you scream.” And, in another surprising twist of pop culture, that is accurate. Space is a vacuum, therefore sound does not have a medium the propagate through, as it is a wave. And if light is a wave… do you see the issue?

Scientists first came up with the sketchyOK, completely bogustheory that space was actually an “ether” that permitted light to pass through it. They discovered that this so-called medium was invisible, weightless, impenetrable to sound, tasteless; but, of course, it could allow light to pass through.

This theory was shot down by Einstein, who theorized that light actually had a wave-particle duality. This basically means that light can behave as a wave and as a particle. Particles of light are called photons, and the most basic explanation of this duality is that the particles move up and down and forward like a wave, meaning they behave like a wave but do not need the constraints that waves have.

And this explains all kinds of thingsand can tell us all kinds of things. Three fascinating things in particular. Three things that we will be discussing.

The first of the three fascinating things of what scientists can tell from observing the spectra of an object is that object’s elemental makeup. You see, every element has a unique “emission spectra”, or the component colors of light that make it up. For example, neon light shines a blend of green, yellow, orange, and red. This means that if scientists analyze light coming from distant objects and break it up into its component colors, they can tell what element that light is coming from. 

Here is an example of an emission spectra diagram:

Image result for emission spectrum
CREDIT: Packer Intersections

What you need to take away from this is the position of the black areas and the color of the colorful lines; the arrangement will be unique for every single element. So, looking at the arrangement of the colors, scientists can understand the element that the light is originating from.

This is highly relevant, especially in the search for exoplanets. By analyzing the light refracting through the atmosphere of exoplanets, scientists can tell what the atmosphere is made up of. Pretty nifty if you ask me!

Second, scientists can tell the temperature of the object by looking at its spectra. They do so by constructing black-body curves.

Now, while this sounds complex, it’s actually quite simple; they’re just diagrams made of the relation between the wavelength given off by an object and its energy output. The bigger the peak, the larger the star and the farther left the peak the warmer the star. Here is an example of a black-body curve:

Image result for blackbody curve definition

Now, before I go farther, here’s a quick rundown on wavelengths of light. Basically, the more compressed the wavelength, the “warmer” and the “bluer” the light, while the more stretched out the wavelength, the “cooler” and the “redder” the light. I know that sounds counter-intuitive, but just bear with me.

When looking at the black-body curve, one notices that the x-axis is the wavelength, or apparent energy, of light, and the y-axis is the radiance, or brightness, of light. When you look at the lines, the peaks all represent stars; the larger the peak of the star’s black-body curve, the more luminous it is, and the smaller the peak of the star’s black-body curve, the dimmer and smaller it is. But that’s not all that a spectrum of light can tell us. 

By first finding out the element of the object and then finding out the apparent wavelength, scientists can tell whether the wavelength is more compressed than usual or more stretched out than usual. With this information, scientists can calculate the speed of the object. Just by looking at its light! Isn’t that amazing?

Using this information, scientists have a nifty calculation and find what they call the “recessional velocity” of a galaxy, or any other astronomical object. They can use the stretch of the spectrum to determine the distance, and the age of the astronomical object as well.

Overall, light, if interpreted correctly, can act as an excellent encyclopedia of sorts to get a lot of information about an object. There are many innovations that have benefited from this depth in understanding of light, and much more to come in the future.

 I hope you enjoyed this article and that you learned something new. Keep your eyes open for more articles coming soon about some more interesting and diverse topics.

Clear skies!