Why are scientists so fascinated with light?

Admittedly, this is a complex subject, but it has a lot to do with the latest astronomical discoveries about planets orbiting distant stars.

Light is a small part of the electromagnetic spectrum that is an essential actor on the stage of the universe. Electromagnetic force is one of the four main forces of nature that emerged from the Big Bang. The strong nuclear force, the weak nuclear force and gravity are the other three.

Light is the part of the spectrum that our eyes are sensitive to and that makes it very important to us humans. The part of the electromagnetic spectrum that our eyes see is composed of blue, green, yellow and red light, a combination that makes white light. The reason we recognize colors is because our eyes have specific retinal cone receptors that are sensitive to those specific regions of the electromagnetic spectrum.

The reason that life forms evolved to have eyes is because of the sun. Sunlight bathes the Earth and ancient creatures evolved to have primitive light sensitive nerve cells that gave them the advantage of seeing their prey, even if it was only shadows or patterns. Eventually, eyes developed and evolved with higher acuity to better spot prey. Some animals, such as birds of prey have very keen eyesight. Wolves have good eyesight in dark situations, giving them the advantage at night. We humans have less eye power than they do, but we don’t hunt at night or fly so we don’t need it.

But, the real reason that science is interested in light is because elements emit specific wavelengths of light when heated. This is where the idea of a spectrum came from. A prism can be used to split white light into different colors of light like a rainbow because it refracts light, which means that it bends different frequencies of light at different angles to crate a spectrum, which is like a rainbow. A spectrum of an element that is heated to emit light provides a way to determine its identity. This discovery paved the way for a lot of chemical analytical instruments not only in visible light but also in ultraviolet and infrared regions of the electromagnetic spectrum, regions that we can’t see.

This idea that a prism can bend light waves is the main reason that we can see. The lens in our eye--which acts like a prism--bends light waves by the process called refraction to focus it on our retina. How does this refraction work? It’s the result of the change in the phase velocity of a light wave front as it passes through medium (a lens or prism). The phase velocity is equal to the wavelength of the light divided by time, and this phase velocity changes because of the optical process of refraction. In other words it gets bent depending on the index of refraction (Index n equals speed of light c divided by the speed of light in the media) of the medium it passes through and the angle of incidence (the angle it enters the medium). The ratio of the sine (trigonometry) of the angle of incidence and the sine of the resultant angle of refraction is equivalent to the ratio of the phase velocities of the two media or equivalent to the opposite ratio of the two indices of refraction. I know, that sounds confusing but to put it in other words: it’s an optical law that light gets bent when it goes from air into some other medium like water or a glass or plastic lens and the amount it gets bent depends on the medium it’s passes through and the angle it enters the medium. This is the reason that something under water appears out of place or bent.

Whew! That’s a lot of stuff to think about. This refraction effect is what makes a spectrum possible and I bring this up because astronomers have been using spectra of stars to determine their structure for quite some time, and recently this method has been used to find extraterrestrial planets around distant stars. That’s because the spectrum of a star has dark lines at specific wavelengths that are equivalent to the absorption of specific elements in the star’s photosphere. These lines shift to the red part of the spectrum if the star is moving away and shift to the blue end of the spectrum if the star is moving toward us. This is one way of detecting if a large Jupiter-like planet orbiting close to the star and causing it to warble or wiggle in our line of sight.

Astronomers also use this shift in a galaxy’s spectrum to determine how quickly it’s moving away due to the expansion of the universe. The further toward the red end of the spectrum that the galaxy’s light is, the faster it’s moving away and this is an indication of how far away it is.

So, you can see how valuable knowing how light works is to astronomy and everyday life. A lot of interesting things have been invented because of the amazing properties of light, including the microscope, telescope, spectrophotometers, your smart phone and Google glass. Amazing!

Thanks for reading.