Download Stars and Galaxies

Stars and
Galaxies
 The three types of galaxies are spiral,
elliptical, and irregular.
 Our sun is in the spiral- shaped Milky Way
galaxy. Spiral galaxies are the most
common type of galaxy found and are oval
shaped. They have a dense center with
spiral arms and are bright and easy to see.
 Elliptical galaxies vary in shape
from nearly spherical to flat disks.
They contain very little dust and
gas. Stars found here are
generally older than those in other
types of galaxies.
 Irregular galaxies have no specific shape
and are hard to see.
• Nebulae are huge clouds of dust and gas
from which new stars are born.
• Steps for the “birth” of stars:
– Large clouds of gas and dust, called nebulae,
collapse due to gravity.
– The collapsing cloud becomes very dense.
– Nuclear reactions involving hydrogen and
helium begin.
– These nuclear reactions power the star.
– A star is born.
 Many stars are found in multiple-star
systems. Alpha Centauri is in a multiple
star system. It is made up of three stars
called a triple star system. Over half of the
stars in the sky have at least one
companion star. Most of these stars are
double-star systems in which two stars
revolve around each other. Double-star
systems or paired stars are called
binary stars.
• A spectrum is used when describing the
movement of stars. A spectrum is a band
of colors formed when white light passes
through a prism.
• Every distant galaxy shows a red shift,
indicating that the universe or star is
expanding or moving away from Earth. A
blue shift would indicate that the universe
or star is moving closer.
• Most astronomers agree that the universe
began with the big bang. The Big Bang
Theory states that the universe began to
expand with the explosion of concentrated
matter and energy and has been
expanding ever since.
• Stars differ in many features, including
size, mass, color, temperature, and
brightness.
• The color of a star is related to its
temperature.
• The main factor that shapes the life and
eventual death of a star is its mass.
• Supergiant stars are the largest of all
stars. They have a diameter up to 1000
times the diameter of the sun. They tend
to die off quickly and are the shortest-lived
stars in the universe.
• Giant stars have a diameter of about 10 to
100 times as large as the sun.
• Medium-sized stars(main sequence), like
our sun, make up the majority of the stars.
Our sun has a diameter of about 1,392,000
kilometers or about 109 times the diameter of Earth.
They very in size from about one-tenth the
size of the sun to about ten times its size.
These stars tend to be very bright
• White dwarfs stars are smaller than the
Earth.
• Nova stars are stars that suddenly
increase in brightness and then get dim.
• Neutron stars are the smallest stars of all.
A typical neutron star has a diameter of
only about 16 kilometers.
• Surface temperature of a star can be
determined by its color. Blue being very
hot 35,000 oC and above and Red being cool
3,000 oC. Our sun is classified in yellow. Its
average surface temperature is around
6,000 oC.
• Most stars are made up primarily of
hydrogen and helium gases.
• A star’s brightness as observed from Earth
is its apparent magnitude. A star’s true
brightness is its absolute magnitude.
 The Hertzsprung-Russell diagram shows
the relationship between a star’s absolute
magnitude and its temperature. This also
includes color.
 The layers of the sun are the
corona, chromosphere,
photosphere, and core.
Solar Prominence ^
• The main factor that affects the
evolution of a star is its starting
mass.