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Chapter 8
6th Grade
Section 1
Stars are huge, bright balls of gas trillions of
kilometers away.
Stars have different colors so they must have
different temperatures.
Stars are made up of gas. The inner layer of a star is
very dense and hot. The outer layers are made up of
cooler gases. Different elements absorb different
wavelengths of light so astronomers can tell what
elements a star is made of.
Section 1
Look through a prism you see a spectrum of colors.
Fire gives off a spectrum.
Astronomers use an instrument called a
spectrograph to break a star’s light into a spectrum.
This gives the astronomers information about the
stars composition and temperature.
When an element emits light only certain colors
show up. The colors are called emission lines----kind
of like fingerprints.
https://www.youtube.com/watch?v=jJvS4uc4TbU
Section 1
A star has both bright and dark emission lines. The
stars atmosphere absorbs certain colors of light in
the spectrum, which causes black lines to appear in
the emission lines.
Absorption spectrum is produced when light from a
hot solid or dense gas passes through a less dense,
cooler gas. The cooler gas absorbs certain portions
of the spectrum. Since some of the spectrum is
absorbed sorting the elements is often difficult.
Section 1
Stars were originally classified according to the
element composition—1800s. Now stars are
classified by temperature.
Class O stars are blue---the hottest. Pg.223.
Originally, astronomers created a system to classify
stars based on brightness. The brightest stars were
first magnitude. The dimmest stars were sixth
magnitude. They used only their eyes.
Section 1
They then began to use telescopes and could see
dimmer stars. They added to the old system of
classifying stars. Positive numbers represent dimmer
stars and negative numbers represent brighter stars.
Can see as far as the 29th magnitude. Brightest is
Sirus -1.4—apparent brightness.
Distance can affect brightness. Sun appears at -26.8
in apparent magnitude but absolute magnitude is
+4.8.
Apparent magnitude: the brightness of a star as seen
from Earth.
Section 1
Absolute Magnitude: is the actual brightness of a star.
Because stars are long distances away astronomers use lightyears to measure the distances from Earth to the stars.
Light year is the distance light travels in one year.
Parallax: an apparent shift in the position of an object when
viewed from different locations. The Earth moves.
Astronomers must use math to figure out the actual distance.
Closer stars seem to move more than distant stars.
The earth faces different stars depending on the time of year--b/c of tilt and rotation. Stars move slowly….pg. 225-226.
Section 2
A star life cycle: first stage: it is a ball of gas and dust.
Gravity pulls the dust and gas together into a sphere. As
the sphere becomes denser it becomes hotter. Hydrogen
changes to helium by a process called nuclear fusion.
When a star dies its materials return to space---sometimes
to form new stars.
Stars can be classified by their size, mass, brightness,
color, temperature, spectrum, and age. Can also be
classified as main-sequence stars, giants, supergiants, and
white dwarfs. Can be reclassified later in its life.
http://didyouknow.org/the-size-of-the-sun-in-comparison/
http://library.thinkquest.org/17940/texts/star/star.html
Section 2
Main-sequence stars: after it forms this is the longest
stage of its life cycle. During this stage energy is
generated in the core of the star as hydrogen atoms
fuse into helium. The fusion releases a lot of energy.
This is where the stars energy comes from. Stays the
same size.
Giants and Supergiants: Third stage of its life cycle.
Red giant: star expands and cools once it is out of
hydrogen. The center of the star shrinks and the
atmosphere expands. Red giants can be 10X bigger
than the sun and supergiants can be 100X bigger.
Section 2
White Dwarfs: Final stage of a star’s life cycle. Can
have the same mass as the sun or smaller. It is a hot
star that is just the leftover center of an older star. It
does not have any hydrogen left and can shine for
billions of years before it cools completely.
Section 2
Ejnar Hertzsprung and Henry Norris Russell
developed the H-R diagram independently---their
ideas were put together. It shows the relationship
between a stars surface temperature and absolute
magnitude. It can also show how stars change over
time.
Read pg. 231….lets talk about it.
Section 2
Large stars may explode and become supernovas,
black holes, neutron stars, or pulsars.
Supernovas: Massive stars use hydrogen faster than
smaller stars. They don’t tend to have long lives
when compared to other stars. When it explodes it
may become a supernova—a gigantic explosion which
throws the stars outer layers into space. It is so
powerful that it can be brighter than a galaxy for a day.
Section 2
Neutron stars: when gravity is so great that protons
and electrons smash together to form neutrons. If it
is spinning it is called a pulsar. It sends out a beam of
radiation across space.
Black holes: so massive light cannot escape it. They
are hard to locate because they do not give off light.
Section 3
Galaxies: large groups of stars, dust and gas. Come in
all shapes and sizes.
Hubble telescope…who can tell me about it?
Spiral galaxies: have a bulge in the center and spiral
arms. The arms are gas, dust, and new stars. Pg. 234235.
The Milky Way: astronomers think our galaxy is a
spiral galaxy. It is hard to see because of gas and
dust.
Section 3
Elliptical Galaxies: 1/3 of all galaxies. Look like blobs
or spheres. Usually have bright centers with very
little dust and gas. Contain mostly old stars---b/c little
to no gas to form new stars. Two types: giant
elliptical galaxies and dwarf elliptical galaxies.
Irregular Galaxies: galaxies that don’t fit into any
certain category or class. Their shape is irregular.
http://htwins.net/scale2/
Section 3
Nebula: large clouds of dust or gas. Found mostly in spiral
galaxies but some are found in elliptical galaxies.
Globular clusters: a group of older stars that look like a ball.
Could be up to 1 million stars in the cluster. Surrounds spiral
galaxies and elliptical galaxies. Located in a spherical halo that
surrounds spiral galaxies.
Open cluster: closely grouped stars—few 100 to few 1000 in a
cluster---usually blue stars. Pg. 236. Usually found in the spiral
disk of a galaxy.
Quasars: star like sources of light that are extremely far away.
One of the most powerful energy sources in the universe.
Thought to be the most distant objects in space.
http://www.phys.vt.edu/%7Ejhs/faq/quasars.html#q2
Section 4
Cosmology: The study of the origin, structure, and
development of the universe.
The universe is expanding….galaxies are moving
apart.
Raisin-Bread Model:
Big Bang Theory: tremendous explosion--13.7 billion
years ago
Section 4
Cosmic background radiation: radiation found in all
directions that scientist believe is left over from the
big bang.
Scientist believe the universe is a cosmic repetition
made up of galaxies, planets, stars, etc.
Scientist think the universe will either continue to
expand forever or it will eventually collapse in on
itself—the opposite of expanding.