Variable Stars.

Twinkle twinkle great big stars
How I wonder how far you are
Like a variable stars in the sky.
You put astronomers’ hope so high.

Imagine a star twinkling without the air in sky being involved. Some kinds of stars really does and they are called variable stars. You can actually plot a curve of brightness of stars which varies over time. And looking at the hips and dips of those curve, you can tell what kinds of stars they are.

There are three major kinds of variable stars.

• Pulsating variable stars are intrinsic variable stars with periods from a few hours (~0.03 days) to >1000 days. These stars vary because their surface layers expand and contract in a periodic (repeating) manner. They are further classified as, 𝛿-Scuti Variables (DSCT), RR Lyrae, Cepheids, Semi-regular Variables, Mira variables

• Eclipsing binary stars consist of stellar systems consisting of two or more stars where the stars undergo eclipses. In their light curves, you should see evidence for a secondary and primary eclipse. The primary and secondary eclipse depths can vary and need not be the same. They are also further classified as, β Persei-type (Algol) binary (EA), 𝛽 Lyrae-type binary (EB) and W Ursae Majoris-type binary (EW).

• Rotational variables are stars whose brightness varies due to large spots on their surfaces. Periods for rotational variables are tied to the rotation of the stars themselves; therefore, their periods can vary widely (~0.5-100 days).

Ancient Egyptians first noted the variability of Algol, an eclipsing binary, over 3000 years ago. Recently, it has even been claimed that aboriginal Australians observed the variability of pulsating red giants long ago and incorporated this discovery into their culture and lore. It is possible that many other ancient cultures noted the variability of bright sources without any record of it surviving to the modern day. The first modern discovery of a periodic variable was made in 1638, when Johannes Holwarda recorded the periodicity of the Mira variable Omicron Ceti. The number of known variable stars gradually increased to ~12 by 1786, ~175 by 1890, ~4000 by 1912 and ~28450 by 1983.

It were also the variable stars which shaped our current understanding of the Cosmology. Astronomer Henrietta Swan Leavitt drew the linear relationships for variable and their distance which was crucial in the observation of Edwin Powel Hubble in 1926. Those were the delta Cepheids of Andromeda which was before known as Nebula and after that observation was the first documented galaxy outside the Milky Way. For that reason, Chepheids are not only Astronomically but also Cosmologically important. With just help of Cepheids we can map the entire universe. Isn’t it freaky?

What gives me goosebumps is we learnt to navigate Earth with the help of stars in the sky when our civilization just sprouted, now we are trying to navigate the entire cosmos again with the help of a kind of stars.