How Observations in Astrophysics are done, and some unexpected discoveries that follow

Hello world, I have been inactive on blogging for a while due to external examinations going on. However, while I was preparing for my exams, I have thought of some astrophysics ideas to be shared on my blog right after exams. Okay, let's start with some 'flashback' of what have been done in astrophysical researches in past century.

One of the most interesting feature in astrophysical observations is that we make a lot of deduction and extract a lot of information, based on one thing, light itself (in more technical term, electromagnetic wave). I will discuss a few aspects and on how so many information can be extracted, purely based on light itself, and on some examples of past historical amazing discoveries that follows.

Before I proceed to astronomical observations and applications of light, I will bring in some intro of bizarre features exhibited by light, an amazing phenomena in many aspects. In 1900s, physicists discovered a very weird property of matters that emits light. When hot matter is heated up to a very high temperature, it glows. The hotter it is, the brighter it glows. But one of the weird features was that, when the object is heated, it gives out a discrete pattern of different colors of light instead of just a spectrum of continuous rainbow lights. It is as if the colors, frequency and wavelength of lights are quantized (can only have certain fixed value, for example, think of Malaysian currency, we can only have 5 cents, 10 cents, 20 cents and so on. We pay in terms of 5 cents as smallest currency instead of 1 cent). And for a matter to emit light, these must be a transition of energy level of electron from higher energy level to lower ones, and only fixed wavelength (and color) of lights emit will imply that electron can be at certain fixed position only.

Quantization, as the diagram implied, is just like a staircase. In our daily life, the concept of quantization is best to be think of as currency note.

Transition of electron from higher energy level to lower ones will emit light, the mystery of emission of light hence is due to electrons 'jumping' to lower level, and since electron can only be at certain level of energy, only certain colors of wavelength is observed.

So why do I explicitly elaborate on property of emission of light on quantum mechanics aspect? Well, discovery of helium comes from this property of physical law. Remember helium,  the element you often see in your high school periodic table (for those who take chemistry)? Helium is extremely rare on earth and only exist in trace amount (can hardly be detected). In 1968, researchers' pursue for discovery of helium is finally accomplished when astrophysicist made an observation of light emitted by sun during solar eclipse. The first discovery of helium, which subsequently lead to the use of helium in balloons, is done through astrophysics! Helium is discovered through emission of light (that certain object will glow and give specific wavelength), though this first discovery has been an indirect observation.

But astrophysical observations through light is not only used to detect undiscovered elements in periodic table alone! There are many more information that we can extract, purely just based on light. I will feature 2 more examples in this post. Another information we can get (other than elements present in certain planets ) is on temperature range of the planet. This is a direct implication from a physical law, Wien's Law, which states that wavelength of light emitted from glowing object is inversely proportional to temperature of glowing object. This means that the greater the wavelength, the lower the temperature, and this actually explains one of the high school students' myth (the fact that redder sun is colder and blue stars are hotter). From the color (and hence the wavelength of light) itself, we can make startlingly accurate prediction of temperature range of a certain stars, and this, is another amazing application of light.

Wien's Law, to show the inversely proportional relationship between wavelength of light and temperature of glowing
object.

The last application of property of light in astrophysics will be on a phenomena called 'gravitational red shift'. This phenomena is based on 2 important laws, 1.) light is electromagnetic wave 2.) Doppler's effect, when there is relative motion between observer and source of wave, there will be apparent change in frequency. I know the definitions of Doppler effect will sound daunting to many tenth graders, so I will offer a simplified explanation of it. Imagine a lorry sounding a horn as it is approaching you and leaving you, when it is approaching you, you will find that the tone of horn will get higher as it is approaching you and tone of horn getting lower as it is leaving you. This is one of the most common Doppler Effect phenomena in daily life (on the apparent change in frequency of wave), and the same property goes to light, an electromagnetic wave. In astronomical observations, there is apparent red shift of light (that the wavelength of observed light emitted from stars), the light gets redder (and hence the increasing wavelength, and the frequency of light gets lower) and as the frequency of emitted light from stars decreases, this implies that the stars observed is leaving and distance itself from mother earth (just like the lorry example). And actually, the expansion of universe is based on gravitational red shift! Again, amazing discoveries that are beautifully linked to each other.

If you don't understand Doppler Effect, imagine a lorry sounding horn as it is coming to you.

I'm only able to post 3 beautiful applications of observation of light in astrophysics. There are more, for sure! And I hope you enjoy reading the tidbits of astrophysics.