Download Chapter 26.4

Chapter 26.4
Groups of Stars
Groups of Stars:
Constellations
Stars that seem to form a picture.
These stars are may or may not be
close to one another.
Constellations
Circumpolar –
• “Circle” North and
South Pole
• Can be seen all year
Ex: Ursa Major (Big
Bear with the Big
Dipper), Draco
(Dragon)
Polaris = North Star
Constellations
Zodiac – “Birthday”
Constellations
“Move” on the ecliptic line
– and can only be seen
during certain months.
The month of your
birthday, you cannot
see your zodiac
constellation because it
is BEHIND the sun.
Binary Stars – Two stars orbit around a
shared center of mass
Alcor and Mizar in
the Dipper appear
as double stars
Over 65% of
stars may have
companion
stars.
“Star System” 2 or more stars orbit around a center of
mass.
Other groups of stars
Open Clusters – Pleiades
A cluster of 100s - 1000s
of stars – in this case
young blue stars
Closed (Globular) Clusters
Older stars densely
packed.
Galaxies = Groups of millions - trillions stars
that are held together by gravity.
Milky Way Stats
100 000 LY across
2 000 LY thick
5 Spiral Arms
Our sun is 2/3 the way out
on the Orion spiral arm.
Moves around center at a
speed of 500,000 mi/hr (It
takes 200 million yrs to complete one
rotation)
Try this simulation:
http://www.telescope.org/btl/data/01904.gif
http://amazingspace.stsci.edu/resources/explorations/g
alaxies-galore/build/index.html
Types of Galaxies
Spiral
A. Central Bulge – Most stars are
located here. Old stars are concentrated
here. Possible location for BLACK HOLES
B. Disk – Flattened pancake of young
stars
C. Arms – Lanes that radiate from center
– Young blue stars
D. Halo – surrounds bulge & arms.
Contains old stars, globular clusters, &
possibly dark matter.
D
B
C
Spirals have
a good deal
of dust & gas
B
A
A
http://www.telescope.org/btl/data/01904.gif
Types of Galaxies
Spiral-Barred –
Types of Galaxies - Ellipitical
Elliptical Galaxies are
shaped like ovals or
footballs. They are dense
and the stars in them are
VERY OLD. Stars “swarm”
around like bees inside.
The giant elliptical galaxy M87 (AAO)
Types of Galaxies – Irregular
No real shape
•Common in distant
(early) universe
•Younger stars, gas, &
dust
•Sometimes a result
of galaxy collisions
Test your knowledge of galaxy types here!:
http://amazing-space.stsci.edu/resources/explorations/galaxies-galore/hunt/index.html
Quasars
Very distant objects that
release energy in outputs
= to that of hundreds of
GALAXIES combined
Quasars may be powered
by SUPERMASSIVE
black holes that “accrete”
galaxies.
Galaxy Collisions
Simulations:
http://www.cita.utoronto.ca/~dubinski/tflops/
The Milky Way is predicted to collide with our larger neighbor Andromeda in
about 5 billion years. (It is approaching us at 670,000 mi/hr). Eventually
they may merge to form an elliptical galaxy. Because stars are so far apart
– it may have no affect … then again – we could get ejected out of our
“place” on the Orion arm due to collision.
Deep Space
Hubble Telescope
takes a picture of
deep space. Each
“star” is actually an
entire galaxy made
up of billions of
stars.
Many of these
galaxies are over
13 billion LY away.
It took light 13
billion years for the
light to travel to us.
Groupings of Galaxies
The Milky Way orbits in a
circle with a group of
neighboring galaxies
called our LOCAL
GROUP.
These GROUP of GALAXIES
orbits with other GROUPS
of GALAXIES in a
SUPERCLUSTER
This is Andromeda – one of the spiral
galaxies in our Local Group (2.2 million
LY)
Our Official Address:
Planet Earth
Sol Solar System
Orion Arm, Milky Way Galaxy
Local Group
Virgo Supercluster
Observable Universe
Magnitude = Star Brightness
Some stars seem brighter than others.
Brightness (Magnitude) depends on..
a. Closeness (closer brighter)
b. Size (bigger = brighter)
c. Temperature (hotter = brighter)
Magnitude Scale
-1
0
Very Bright
1
Bright
2
3
4
Dim
Absolute Magnitude = How bright something REALLY is
Apparent Magnitude = How bright it SEEMS (maybe its close)
Magnitude Questions
http://www.enchantedlearning.com/subjects/astronomy/stars/bright.shtml
Star A has a magnitude of 2
Star B has a magnitude of 1
1. Which is brighter?
2. Bernard’s Star is one of the closest stars
to us. It has a magnitude of 8. What
conclusions can you make about Proxima
Centauri based on this?
Parallax
http://instruct1.cit.cornell.edu/courses/astro1
01/java/parallax/parallax.html
Black Hole Song/Visual
http://www.rdrop.com/users/green/school/for
m.htm