Chapter 15 Jennifer Blazejack

Introduction
15.1- Islands of Stars
15.2- Distances of Galaxies
15.3- Galaxy Evolution
Conclusion
Introduction
Student PowerPoints were presented to the class. Then we discussed issues and Prizes related to Astronomy.
15.1- Islands of Stars
There are three types of galaxies: Spiral, Elliptical, and Irregular. Our Milky Way is concerned a spiral galaxy because of the "arms" it contains. Elliptical are more of a disk type while Irregular don't have a spiral or disk shape. Sometimes Spirals and Ellipticals can combine and form Irregular galaxies (as shown in the video during class). Blue-white stars found in any of the galaxies outshine the red-yellow stars which are old and not as hot. Galaxies are grouped together in "groups" or "clusters of galaxies".
15.2- Distances of Galaxies
There are various ways to measure distances: radar (like those used in World War II), parallax (using Earth-Sun distance in January and June), main-sequence fitting ("Oh Be A Fine Guy/Girl, Kiss Me!"), cephids (stars), distant standards (white dwarfs), and Hubble's Law (Blue frequency is high while red frequency is low).  Luminosity of a star alone cannot measure distance because some stars can have the same luminosity, but be at different distances- the candle versus a lighthouse example given in class. Cosmology is the study of the structure and evolution of the universe- distance can help determine the age.
15.3- Galaxy Evolution
Galaxies can collide and create another galaxy (just like white dwarfs colliding can create black holes). Just as stated before, Spiral and Elliptical can collide and form Irregular galaxies. Also, Hubble's Law is wrong- it was originally thought that the universe was expanding, but it is not. The universe is actually accelerating, like a balloon filled with air.
Conclusion
We very briefly discussed 15.4 and were told that two students final grades were in. It is important to turn in the term paper and PowerPoint before next lecture. Students were encouraged to still come to class next week.