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. 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 Stars vary in size, color, and mass Some have a diameter as small as 20 km Some have a diameter as small as 20 km Others have diameters as big as 1 billion 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 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. Light from the sun takes about 8 minutes to reach the earth. So the sun is 8 light-minutes from 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 brightest star in the night sky has an apparent magnitude of -1.46 The sun has an apparent magnitude of -26.8 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 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 Main-sequence stars are visible in the night sky and the sun A large, bright star that is cool is called a giant A large, bright star that is cool is called a giant Super-giants are just larger versions of giants Super-giants are just larger versions of giants A very hot but small and dim star is called a white dwarf A very hot but small and dim star is called a white dwarf