continued from Starlit Sky: 15. Virgo
In the month of Jun at around 8-9 pm (Northern hemisphere) lift up your head, right on top you will find the Corvus and Bootis constellations.
Let me help you locate these constellations.
Use Spica of Virgo constellation to travel a bit south and there you can see 4 stars, forming sort of a quadrilateral. That is the Corvus constellation.
Corvus means raven in Latin. Gamma Corvi also called Gienah is the brightest among all the stars in the constellation. Gienah is an aging blue giant and it is almost 10 times bigger than our Sun.
In the Indian Astronimical system, the Corvus is not seen as a crow. It is visualied as a fist or Hasta. One of the 27 stars of the lunar system is Hasta. Gienah is called Hasta in this system.
Move your eyes back to Spica of Virgo. Now go in north-easternly direction and you will see a very bright star along with faintly lit stars forming what looks to me like a kite. To the ancient star gazers, it looked like a herdsman or a man with a plow. The plow being the big dipper that is to the west of this constellation. You remember big dipper, right? the polar bear? Right! That’s the one. They named him Bootis.
The bright star of Bootis is Arcturus. Arcturus is the fourth brightest object in the sky. It is an orange giant.
Arcturus is called Swati in the Indian Astronomical system.
The life of a star begins as a gaseous mass swirling around a core. The star material starts collapsing under its own gravity. The temperature heats up and nuclear fusion starts. Hydrogen atoms are fused together to form helium. This releases enormous energy and star starts emitting light. As long as there is hydrogen available, the fusion continues. When the hydrogen is exhausted, the helium now starts fusing together.
Depending upon the size of the original star, there can now be two paths for the star to take.
If it is a small star, then as the helium core fuses to form carbon, the outer shell cools and expands and the star becomes a red giant. Eventually when the helium too runs out, the outer shell drifts off as gases. The remaining core shines less and less and becomes a white dwarf and slowly becomes a black dwarf.
On the other hand if the star was massive, the path is different. Once all the hydrogen is converted to helium, the star expands and becomes a Red super giant. Slowly the helium atoms start fusing and eventually an iron core is created in the star. The core can no longer sustain and the star collapses and explodes into a supernova. All the outer shell is dissipated as gases. Sometimes the core is not destroyed, and what is left behind is a very very dense neutron star. If the mass of the neutron star is more than 3 solar masses, it becomes a black hole. A black hole has so much gravity that even light cannot escape it.
The temperature of the star can be measured by the colour. Red, oranges, yellows are cooler than blues.
to be continued……………..