Interstellar Gas
LEARNING OBJECTIVES By the end of this section, you will be able to: Interstellar gas, depending on where it is located, can be as cold as a few degrees above absolute zero or as hot as a million degrees or…
Bloom Code Studio
The Interstellar Medium
LEARNING OBJECTIVES By the end of this section, you will be able to: Astronomers refer to all the material between stars as interstellar matter; the entire collection of interstellar matter is called the interstellar medium (ISM). Some interstellar material is concentrated into giant…
Thinking Ahead
Figure 20.1 NGC 3603 and Its Parent Cloud. This image, taken by the Hubble Space Telescope, shows the young star cluster NGC 3603 interacting with the cloud of gas from which it recently formed. The bright blue stars of the cluster have blown…
Summary
Fundamental Units of Distance Early measurements of length were based on human dimensions, but today, we use worldwide standards that specify lengths in units such as the meter. Distances within the solar system are now determined by timing how long…
The H–R Diagram and Cosmic Distances
LEARNING OBJECTIVES By the end of this section, you will be able to: Variable stars are not the only way that we can estimate the luminosity of stars. Another way involves the H–R diagram, which shows that the intrinsic brightness…
Variable Stars: One Key to Cosmic Distances
LEARNING OBJECTIVES By the end of this section, you will be able to: Let’s briefly review the key reasons that measuring distances to the stars is such a struggle. As discussed in The Brightness of Stars, our problem is that stars…
Surveying the Stars
LEARNING OBJECTIVES By the end of this section, you will be able to: It is an enormous step to go from the planets to the stars. For example, our Voyager 1 probe, which was launched in 1977, has now traveled…
Fundamental Units of Distance
LEARNING OBJECTIVES By the end of this section, you will be able to: The first measures of distances were based on human dimensions—the inch as the distance between knuckles on the finger, or the yard as the span from the…
Thinking Ahead
Figure 19.1 Globular Cluster M80. This beautiful image shows a giant cluster of stars called Messier 80, located about 28,000 light-years from Earth. Such crowded groups, which astronomers call globular clusters, contain hundreds of thousands of stars, including some of the RR Lyrae…
Summary
A Stellar Census To understand the properties of stars, we must make wide-ranging surveys. We find the stars that appear brightest to our eyes are bright primarily because they are intrinsically very luminous, not because they are the closest to…