When it comes to Astronomy, observing the night sky is what makes us reveal all the mysteries hidden out there. While observing the night sky, the ancient astronomers found that these stars varied in their sizes, brightness and color but later they observed that there were certain stars which shows periodic changes in their intensities. It's in the early 1900s when Henrietta Leavitt working at Harvard University observed the first variable star while analyzing the photographic plates of the night sky. Leavitt studied these stars and made a great discovery that changed the understanding of our universe. But how did this discovery end up unraveling a great mystery about our universe? So, the story goes like this, On October 6th, 1923 Edwin Hubble found the variable star called the Cepheid variable which was present in the entirely different galaxy, the Andromeda which was previously considered as a glowing gas cloud or a nebula quite far from our Earth. The observation of various variable stars in the night sky led to the understanding that our galaxy does not define the universe, there are so many more galaxies many light years away from us.
What varies in a variable star?
Variable stars are the ones who change their brightness or spectrum due to some reasons. When stars are formed, they are highly variable and as they evolve, they settle into a red giant like our sun which can be changed into a variable star when they start pulsating. Every star is going to be a variable star at some point in its life. There can be different reasons for a star to be variable such as shrinking and expanding of a star, revolving around some other star and accordingly they are classified into intrinsic and extrinsic variable stars.
We can observe the variable stars with our unaided eyes or using astronomical instruments like telescopes and cameras to observe and comparatively analyse the data and the variations in them. On these bases of all data a light curve can be constructed. The image below shows the graph of eclipsing binary stars as brightness changes due to a star eclipsing another which gradually shows changes in the brightness of the star.
While in observatories, variable stars are analysed using photometry and spectroscopy. The light curves plotted based on the observations helps us to see the change in its period, amplitude, the magnitude of the star. The study of variable stars is important to study stellar properties of distant stars such as mass, radius, luminosity, temperature, their structure, evolution and lot more about the life of stars in our universe.