Intensity and Luminosity in Stellar Physics
This section explores the fundamental concepts of intensity and luminosity in the context of stellar physics.
Luminosity L is defined as the rate of light energy released or the power output of a star. In contrast, intensity I represents the power received from a star per unit area, measured in W/m². The relationship between these two quantities is governed by the inverse square law: I ∝ 1/d², where d is the distance from the star.
Definition: Luminosity is the total energy output of a star, while intensity is the energy received per unit area at a specific distance.
The concept of standard candles is introduced as a method for determining astronomical distances. These are objects with known luminosity, allowing astronomers to calculate distances by measuring the intensity of light received on Earth.
Example: Type Ia supernovae are often used as standard candles due to their consistent peak luminosity.
The Hertzsprung-Russell diagram is presented as a powerful tool for classifying stars based on their luminosity and temperature. It shows the relationship between these properties and allows for the identification of different spectral classes.
Highlight: The main sequence on the HR diagram represents stable stars that will remain in that state for most of their lives.
The section concludes with an explanation of trigonometric parallax, a method used to measure the distances to nearby stars. Various units of astronomical distance are defined, including the astronomical unit AU, parsec pc, and light-year ly.
Vocabulary: Parallax is the apparent change in position of a nearby star relative to distant background stars, caused by Earth's orbit around the Sun.
