Download Stars and Galaxies

Stars and Galaxies
Section 1
Stars
A.
Patterns of stars—constellations
A. Ancient cultures used mythology or
everyday items to name constellations
B. Modern astronomy studies 88
constellations
C. Some constellations are not visible all
year because Earth revolves around
the Sun
D. Circumpolar constellations in the
northern sky appear to circle around
Polaris and are visible all year
B.
C.
Star magnitude
A. Absolute magnitude—measure of the
amount of light a star actually gives off
B. Apparent magnitude—measure of the
amount of a star’s light received on
Earth
Space measurement
A. Astronomers measure a star’s
parallax—shift in its position when
viewed from two different angles
B. Distance is measured in light-years—
the distance light travels in a year
D.
Star properties
A. Color indicates temperature
A. Hot stars are blue-white
B. Cool stars look orange or red
C. Yellow stars like the Sun are medium
temperature
B. A spectroscope breaks the visible light
from a star into a spectrum
A. Spectrum indicates elements in the
star’s atmosphere
Stars and Galaxies
Section 2
The Sun
Sun’s layers—energy created in the core
moves outward through the radiation zone
and the convection zone and into the
Sun’s atmosphere
 Sun’s atmosphere

Photosphere—lowest layer gives off light and
is about 6,000 K
 Chromosphere is the next layer about 2,000
km above the photosphere
 Extending millions of km into space, the 2
million K corona releases charged particles as
solar wind


Surface features

Sunspots—dark areas cooler than their
surroundings
 Temporary
features which come and go over days,
weeks, or months
 Increase and decrease in a 10 to 11 year pattern
called solar activity cycle

Sunspots are related to intense magnetic
fields
 Magnetic
fields may cause prominences—huge,
arching gas columns
 Violent eruptions near a sunspot are called solar
flares

Bright coronal mass ejections (CMEs) appear
as a halo around the Sun when emitted in the
Earth’s direction
 Highly
charged solar wind particles can disrupt
radio signals
 Near Earth’s polar areas solar wind material can
create light called an aurora

Sun is mostly average
Middle-aged star
 Typical absolute magnitude with yellow light
 Unusual—Sun is not part of a multiple star
system or cluster

Stars and Galaxies
Section 3
Evolution of Stars

Classifying stars—Ejnar Hertzsprung and
Henry Russell graphed stars by
temperature and absolute magnitude in a
H-R diagram
 Main Sequence—diagonal band on H-R
diagram
Upper left—hot, blue, bright stars
Lower right—cool, red, dim stars
Middle—average yellow stars like the
Sun
 Dwarfs and giants—the ten percent of
stars that don’t fall in the main sequence
Fusion of hydrogen occurs in star cores
releasing huge amounts of energy
 Evolution of stars
 A nebula contracts and breaks apart
from the instability caused by gravity
Temperatures in each nebula chunk
increase as particles move closer
together
At 10 million K fusion begins and
energy from a new star radiates into
space


The new main sequence star balances
pressure from fusion heat with gravity
Balance is lost when core hydrogen fuel is
used up
 Core contracts and heats up causing outer
layers to expand and cool
 Star becomes a giant as it expands and outer
layers cool
 Helium nuclei fuse to form core of carbon


A white dwarf star forms from the giant
star
Helium is exhausted and outer layers escape
into space
 Core contracts into hot, dense, small star

In massive stars fusion causes higher
temperatures and greater expansion into a
supergiant
 Eventually fusion stops as iron is formed
 The core crashes inward causing the
outer part to explode as an incredibly
bright supernova
 The collapsed core of a supernova may
form a neutron star of extremely high
density

The mass of a tremendously big
supernova core can collapse to a point,
forming a black hole
 Gravity is so strong not even light can
escape
 Beyond a black hole’s event horizon
gravity operates as it would before the
mass collapsed
 Matter emitted by a star over its life time is
recycled and can become part of a new
nebula

Stars and Galaxies
Section 4
Galaxies and the Universe

Galaxy—gravity holds together a large
collection of stars, gas, and dust
Earth’s galaxy is Milky Way which is part of a
galaxy cluster named the Local Group
 Spiral galaxies—spiral arms wind out from
inner section; some have barred spirals with
stars and gas in a central bar
 Elliptical galaxies—large, three-dimensional
ellipses; most common shape
 Irregular galaxies—smaller, less common
galaxies with various different shapes


The Milky Way Galaxy—usually classified
as a spiral galaxy
May contain one trillion stars
 About 100,000 light-years wide
 Sun orbits galaxy’s core every 225 million
years


Theories on the origin of the universe
Steady state theory—universe has always
existed just as it is now
 Oscillating model—universe expands and
contracts repeatedly over time


Universe is expanding
 Doppler shift—light changes as it moves
toward or away from an object
Starlight moving toward Earth shifts to
blue-violet end of spectrum
Starlight moving away from Earth
shifts to red end of spectrum
 All galaxies outside the Local Group
indicate a red shift in their spectra
indicating they are moving away from
Earth

Big Bang Theory—holds that universe
began 13.7 billion years ago with huge
explosion that caused expansion
everywhere at the same time
 Galaxies more than 10 billion light-years
away give information about a young
universe
 Whether the universe may eventually
stop expanding and begin contracting is
unknown