Chapter 27 Stars and Galaxies

Chapter 27Chapter 27 Stars and Galaxies Stars and Galaxies

Section 1Section 1

27.1 Characteristics of Stars27.1 Characteristics of Stars

A A starstar is a body of gases that gives off a is a body of gases that gives off a tremendous amount of radiant energy in tremendous amount of radiant energy in the form of heat and light.the form of heat and light.

Stars vary in size, color, and massStars vary in size, color, and massSome have a diameter as small as 20 kmSome have a diameter as small as 20 kmOthers have diameters as big as Others have diameters as big as

1 billion km1 billion km


A A spectrometerspectrometer is a device that separates is a device that separates light into different colors, or wavelengthslight into different colors, or wavelengths

Starlight passing through a device for separating light produces a display of colors and lines called a spectrum


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


Light from the sun takes about 8 minutes Light from the sun takes about 8 minutes to reach the earth.to reach the earth.

So the sun is So the sun is 8 light-minutes8 light-minutes from the from the earthearth

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.


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


The brightest star in the night sky has an The brightest star in the night sky has an apparent magnitude of -1.46apparent magnitude of -1.46

The sun has an apparent magnitude of The sun has an apparent magnitude of -26.8-26.8

So, an apparent magnitude of -30 would So, an apparent magnitude of -30 would be the brightest and +30 would be the be the brightest and +30 would be the faintest faintest


Main-sequence starsMain-sequence stars are visible in the are visible in the night sky and the sunnight sky and the sun

A large, bright star that is cool is called a A large, bright star that is cool is called a giantgiant

Super-giantsSuper-giants are just larger versions of are just larger versions of giantsgiants

A very hot but small and dim star is called A very hot but small and dim star is called a a white dwarfwhite dwarf

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Chapter 27 Stars and Galaxies