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Stars are hundreds of thousands of times farther away from us than the planets are from us. The nearest star (other than the Sun) is so far away that the fastest spacecraft the human race has built so far would take almost several tens of thousands of years to get there. Yet we are a curious and ambitious species, and we want to know how those stars are born, live out their lives, and die. How can we learn about objects that are so remote and beyond our physical grasp? This chapter gives you an idea of how we learn about the stars and what we find about the stars. Because the stars in our galaxy are so far away, they appear as just pinpoints of light in even the most powerful of telescopes on the ground or in space. We have to rely on the information encoded in the feeble starlight. Before continuing with this chapter, be sure to review carefully the concepts in the Electromagnetic Radiation (Light) chapter so that you will understand this Stellar Properties chapter.
By the end of the chapter you will see there is an internal consistency of star properties and that these points of light are very different from the other points of light that wander among them (the planets). Once we were able to measure the distances to the stars, we found that they are very luminous compared to the planets. There are like our Sun. We also discovered that there is a depth to our universe---the stars are not all at the same distance from us. And we found that the universe is a lot bigger than we thought before.
The stars are very luminous things like our Sun but are they really like our Sun? Are they hot like the Sun? Temperature measurements show us that the star are hot compared to the planets and more like the Sun. The red ones are cooler---only 2500 to 3500 K, the yellow ones are 5000 to 7000 K, the white ones are 9000 to 15000 K, and the blue ones are 20,000 to 50,000 K. Are the stars large in diameter like the Sun? Size measurements show that the stars are big compared to the planets; they are large like the Sun. Things that are big and hot should also be massive like the Sun if they are like the Sun. Mass measurements show the stars do have a lot more material in them than the planets and are more like the Sun.
This chapter is the most math intensive of the chapters in this book (chapter 5 is the next most math intensive one), but remember to keep your eye on the "bigger picture": how we know what we know and don't get bogged down with the formulae. If your math skills are rusty, study the math review appendix and do not hesitate to ask your astronomy instructor for help. The vocabulary terms are in boldface.
last updated: June 7, 2010