Chapter 26.4Groups 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

ConstellationsZodiac – “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.

http://www.allthesky.com/constellations/orion/big.jpg

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 starsOpen Clusters – Pleiades

A cluster of 100s - 1000s of stars – in this case young blue stars

Closed (Globular) ClustersOlder stars densely packed.

Galaxies = Groups of millions - trillions stars

that are held together by gravity.

http://www.telescope.org/btl/data/01904.gif

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://amazing-space.stsci.edu/resources/explorations/galaxies-galore/build/index.html

Types of GalaxiesSpiral

http://www.telescope.org/btl/data/01904.gif

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.

Spirals have a good deal of dust & gas

A

A

B

B

C

D

Types of Galaxies - Ellipitical

The giant elliptical galaxy M87 (AAO)

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.

Types of GalaxiesSpiral-Barred –

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 CollisionsSimulations: 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 SpaceHubble 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 GalaxiesThe 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

Our Official Address:

Planet Earth

Sol Solar System

Orion Arm, Milky Way Galaxy

Local Group

Virgo Supercluster

Observable Universe

This is Andromeda – one of the spiral galaxies in our Local Group (2.2 million LY)

Magnitude = Star BrightnessSome 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 1 2 3 4

Very Bright Bright Dim

Absolute Magnitude = How bright something REALLY is

Apparent Magnitude = How bright it SEEMS (maybe its close)

Magnitude Questionshttp://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/astro101/java/parallax/parallax.html

Black Hole Song/Visual

http://www.rdrop.com/users/green/school/form.htm