5: Stars
- Page ID
- 55005
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- The Sun, our star, has several layers beneath the visible surface: the core, radiative zone, and convective zone. These, in turn, are surrounded by a number of layers that make up the solar atmosphere. In order of increasing distance from the center of the Sun, they are the photosphere, with a temperature that ranges from 4500 K to about 6800 K; the chromosphere, with a typical temperature of 104 K; the transition region, a zone that may be only a few kilometers thick.
- 5.2: Understanding Stars
- This section examines how astronomers determine the physical properties of stars from the light they observe. It explores stellar brightness, color, and spectra and shows how these observations can reveal properties such as temperature, composition, motion, and size. These characteristics are brought together in the H-R diagram, an important tool for comparing stars and recognizing patterns among stellar populations.
- 5.3: Stellar Evolution
- This section follows the life cycle of stars from their formation in clouds of gas and dust through the final stages of their evolution. It examines how a star’s position on the H-R diagram changes over time and emphasizes the importance of stellar mass in determining its evolutionary path. The section traces the development of low- and high-mass stars from the main sequence through red giant stages and ultimately to very different stellar endpoints.
Chapter 5: Stars — Introduction
The Sun is the star we know best. Because it is close enough for astronomers to study in detail, it provides an important starting point for understanding the billions of other stars throughout our galaxy. Although stars appear as tiny points of light in the night sky, observations of their light allow astronomers to determine surprisingly detailed information about their physical properties.
In this chapter, we will begin with the structure and composition of the Sun before turning our attention to other stars. We will examine how astronomers use brightness, color, and spectra to determine properties such as stellar temperature, composition, size, and motion. These characteristics also allow us to organize stars using the Hertzsprung-Russell (H-R) diagram, one of the most useful tools for understanding stellar populations and evolution.
Stars are not permanent objects. They form within clouds of gas and dust and change throughout their lives as conditions within their interiors evolve. A star's mass plays a particularly important role in determining the path it follows. Some stars eventually shed their outer layers and leave behind dense stellar remnants, while more massive stars can end their lives in tremendous explosions.
By following stars from their formation through their final stages, we can see how observations of individual stars fit into a much larger story of stellar evolution. That story will also help us understand how stars contribute to the changing composition of galaxies and the universe.