Mindblown: a blog about philosophy.
-
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 farther from Earth than any other spacecraft. As this is written in 2016, Voyager 1…
-
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 extended index finger to the nose of the British king. Later, the requirements of commerce…
-
Thinking Ahead
How large is the universe? What is the most distant object we can see? These are among the most fundamental questions astronomers can ask. But just as babies must crawl before they can take their first halting steps, so too must we start with a more modest question: How far away are the stars? And…
-
The H–R Diagram
Learning Objectives By the end of this section, you will be able to: In this chapter and Analyzing Starlight, we described some of the characteristics by which we might classify stars and how those are measured. These ideas are summarized in Table 18.2. We have also given an example of a relationship between two of these characteristics…
-
Diameters of Stars
Learning Objectives By the end of this section, you will be able to: It is easy to measure the diameter of the Sun. Its angular diameter—that is, its apparent size on the sky—is about 1/2°. If we know the angle the Sun takes up in the sky and how far away it is, we can…
-
Measuring Stellar Masses
Learning Objectives By the end of this section, you will be able to: The mass of a star—how much material it contains—is one of its most important characteristics. If we know a star’s mass, as we shall see, we can estimate how long it will shine and what its ultimate fate will be. Yet the…
-
A Stellar Census
Learning Objectives By the end of this section, you will be able to: Before we can make our own survey, we need to agree on a unit of distance appropriate to the objects we are studying. The stars are all so far away that kilometers (and even astronomical units) would be very cumbersome to use;…
-
Thinking Ahead
How do stars form? How long do they live? And how do they die? Stop and think how hard it is to answer these questions. Stars live such a long time that nothing much can be gained from staring at one for a human lifetime. To discover how stars evolve from birth to death, it…
-
Using Spectra to Measure Stellar Radius, Composition, and Motion
Learning Objectives By the end of this section, you will be able to: Analyzing the spectrum of a star can teach us all kinds of things in addition to its temperature. We can measure its detailed chemical composition as well as the pressure in its atmosphere. From the pressure, we get clues about its size.…
-
The Spectra of Stars (and Brown Dwarfs)
Learning Objectives By the end of this section, you will be able to: Measuring colors is only one way of analyzing starlight. Another way is to use a spectrograph to spread out the light into a spectrum (see the Radiation and Spectra and the Astronomical Instruments chapters). In 1814, the German physicist Joseph Fraunhofer observed that the spectrum of the Sun…
Got any book recommendations?