Chapter 27 Stars and Galaxies

1. Chapter 27 Stars and Galaxies Section 1

2. 27.1 Characteristics of Stars • A star is a body of gases that gives off a tremendous amount of radiant energy in the form of heat and light. • Stars vary in size, color, and mass • Some have a diameter as small as 20 km • Others have diameters as big as 1 billion km

3. 27.1 Characteristics of Stars • A spectrometer is a device that separates light into different colors, or wavelengths • Starlight passing through a device for separating light produces a display of colors and lines called a spectrum

4. 27.1 Characteristics of Stars • An apparent shift in the wavelength of light emitted by a light source moving toward or away from an observer is known as The Doppler Effect • A star moving toward the earth would display a blue shift • A star moving away from the earth would display a red shift

5. 27.1 Characteristics of Stars • Light from the sun takes about 8 minutes to reach the earth. • So the sun is 8 light-minutes from the earth • The apparent change in the position of an object resulting from a change in the angle or in the position from which it is viewed is called parallax.

6. 27.1 Characteristics of Stars • The apparent magnitude of a star is a measure of its brightness as it appears from the earth. • The faintest star that can be seen by the unaided eye has an apparent magnitude of +6. • The faintest star that can be seen with a telescope has an apparent magnitude of +29

7. 27.1 Characteristics of Stars • The brightest star in the night sky has an apparent magnitude of -1.46 • The sun has an apparent magnitude of -26.8 • So, an apparent magnitude of -30 would be the brightest and +30 would be the faintest

8. 27.1 Characteristics of Stars • Main-sequence stars are visible in the night sky and the sun • A large, bright star that is cool is called a giant • Super-giants are just larger versions of giants • A very hot but small and dim star is called a white dwarf