Chapter 27
Stars and Galaxies
Section 1
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

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

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

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.

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

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

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
