Chapter 1
Earth Science
Course: Elementary Education Multiple Subjects 7001
Subject: Elementary Education Science Subtest 7005
Chapter: Earth Science
1. Stars and Galaxies
Stars are massive celestial objects composed primarily of hydrogen and helium. Through a process called nuclear fusion, hydrogen atoms in a star’s core fuse to form helium, releasing vast amounts of energy in the form of light and heat. This process creates the electromagnetic radiation that we observe as starlight. The lifecycle of a star depends heavily on its mass. Low-mass stars (like the Sun) have long, stable lifespans, while high-mass stars evolve more quickly and end in supernova explosions.
Stars are categorized by their temperature and spectral class (O, B, A, F, G, K, M), with O-type stars being the hottest and bluest, and M-type being the coolest and reddest. The Hertzsprung-Russell diagram is a graph that plots stars based on their luminosity and temperature, showing the main sequence (where most stars lie during their stable phase), giants, supergiants, and white dwarfs.