Up in the sky

Up in the sky, shining bright

Little points of light, in the night

...was all that humans knew about stars at one point of time. With time and patience, knowledge grew. Some of the earliest records are from around 2300 BC, when the Chinese started naming stars, and 750 BC, when Babylonians made moon calendars. But soon information started flooding in and a lot of humans lost track of what was being discovered. Millennia later. So as Astro Club, we held a lecture, one among a series called Syzygy. Syzygy refers to a straight line configuration of three celestial bodies. The series will have lectures on different topics. This one, held on 23rd, was about stars and a bit of what we know about them. The turnout was decent and included a few professors as well.

           

Humans, in general, have something of a history of being fickle minded when it comes to theories on how things work, more so in the case of Astronomy. Ptolemy listed forty-eight constellations and believed in the geocentric theory. Along came Copernicus to burst his bubble. He came up with a theory that had the Sun at the centre of the Universe and not the Earth. We now know that neither of them are true. But at that point of time, the theory faced a good deal of opposition while still gaining popularity, as it was closer to the truth. Then came Kepler's laws, which gave us a detailed explanation of the motion of planets, Galileo's telescope, with which he was able to see Jupiter’s “ears”, Newton laws and finally, the Messier catalogue. THE MESSIER CATALOGUE which is still the most famous list of heavenly objects.

Soon enough, they got bored of just looking at the stars and standing there with their mouths gaping open. The emphasis then shifted to looking at the physics behind stars. It went beyond observation and cataloging. Till that time, as far as the people were concerned, stars were just humongous balls of cotton that had been set on fire.

OOH! Look. I’m holding a star! :)

And that’s when they analyzed Vega’s spectrum. Just like an excited kid with a prism pointed at the sun, the scientists had a look at the spectrum caused by light from Vega. And that’s when they went like OMGWTF?! The spectrum was different from the one that belonged to the sun. So our sun, was indeed unique, just like every other star out there. Spectroscopy provided a method of looking into stars, literally. There are three kinds of spectra: continuous, emission, absorption. Stars were upgraded from fiery cotton balls to hot balls of gas held together by tremendous gravitational forces. At such high temperature, the density is no barrier to using ideal gas equations, as the kinetic energy is still a lot higher than the potential energy. And the best part is, that you don't even have to be a genius to figure out the maths behind it. Sure, you might not have heard of some of the weird theorems and formulae that are used in the process, but down on the ground level, they are all just basic physics that we have all learned at school. Depending on how the dark or bright lines in a star’s spectrum were placed, you could tell what elements the star was made out of, the temperature of the star, how fast and where the star was moving, the density of the star and much, much more. 

The different types of spectra that are used to study star

The color of stars are classified into 7 spectral types where(ironically) O, or blue  stars, are the hottest and M and K, or the red stars, are the coolest. Apart from that, stars are also divided into categories based on their sizes and luminosity. In the 1900s, two scientists came up with a temperature-luminosity graph for the stars, called the Hertzsprung, Russel diagram, or HR for short. They discovered that white dwarfs, giants and super giants didn't fit in in the same place as most of the other “normal” stars. 

The HR diagram, simplified

Naturally, observation and theorems followed and the quest goes on...

“...it was in the nature of things that we shall never know what stars are...”

...will it ever end?