Introduction to Astronomy
Stars
Introduction to Astronomy
Stars
Overview
Classification
Main Sequence
Others
Introduction to Astronomy
Stars
Classification based on color/temperature
Light and other radiation are messengers from objects in the universe.
Introduction to Astronomy
Stars
Classification based on Color/Temperature
Recall :
The most dominant color of a star indicates its surface temperature
Introduction to Astronomy
Wien's displacement law
Stars
Classification based on Color/Temperature
Introduction to Astronomy
Q: What color signifies an object at a higher temperature? Red or Blue?
Stars
Classification based on Color/Temperature
Introduction to Astronomy
Stars
e.g. The Sun
Visible Spectrum of the Sun. Our star’s spectrum is crossed by dark lines produced by atoms in the solar atmosphere that absorb light at certain wavelengths. (credit: modification of work by Nigel Sharp, NOAO/National Solar Observatory at Kitt Peak/AURA, and the National Science Foundation)
Introduction to Astronomy
Stars
Example Star
Introduction to Astronomy
Stars
Example Star
Introduction to Astronomy
Stars
Classification
Introduction to Astronomy
Stars
An Analogy
Introduction to Astronomy
Stars
An Analogy
Introduction to Astronomy
Stars
Star Groups
Introduction to Astronomy
Stars
Star Groups
Introduction to Astronomy
Stars
Star Groups
Introduction to Astronomy
Stars
Main Sequence
After condensation and ignition of a star, it generates thermal energy in its dense core region through nuclear fusion of hydrogen into helium. During this stage of the star's lifetime, it is located on the main sequence at a position determined primarily by its mass, but also based upon its chemical composition and age. The cores of main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. The strong dependence of the rate of energy generation on temperature and pressure helps to sustain this balance. Energy generated at the core makes its way to the surface and is radiated away at the photosphere. The energy is carried by either radiation or convection, with the latter occurring in regions with steeper temperature gradients, higher opacity or both.