Organizing the cosmosOrganizing the cosmosGalaxies Galaxies

& our & our Universe Universe

There is still uncertainty on exactly how the universe and our solar system formed. There are many theories but no one knows for sure. By studying distant galaxies astronomers may

one day determine how the universe was formed

What is a Galaxy?What is a Galaxy?

A large group of A large group of stars, dust, and stars, dust, and gases held gases held together by gravitytogether by gravity

Interstellar Interstellar Matter- Matter- dust and dust and gases found gases found between starsbetween stars

Our Milky WayOur Milky Way

SizeSize: large spiral disk : large spiral disk 100,000 light year wide & 100,000 light year wide & 10,000 thick10,000 thick

StructureStructure: Spiral disk-like : Spiral disk-like shape like our solar shape like our solar systemsystem

Galaxy is Greek for milkGalaxy is Greek for milk

**Our Sun is 1 of 100 Billion **Our Sun is 1 of 100 Billion stars in the stars in the Milky Way Milky Way GalaxyGalaxy

The sun rotates around the The sun rotates around the galaxy once about every 240 galaxy once about every 240 million yearsmillion years

Pinwheel GalaxyPinwheel GalaxyLargest galaxy known to Largest galaxy known to

datedate

The giant spiral disk of The giant spiral disk of stars, dust and gas is stars, dust and gas is 170,000 light-years 170,000 light-years across or across or nearly twice nearly twice the diameter of our Milky the diameter of our Milky WayWay. The galaxy is . The galaxy is estimated to contain at estimated to contain at least one trillion stars. least one trillion stars. Approximately 100 billion Approximately 100 billion of these stars alone of these stars alone might be like our Sun in might be like our Sun in terms of temperature terms of temperature and lifetime. and lifetime.

Andromeda GalaxyAndromeda Galaxy Our closest neighborOur closest neighbor

It is visible as a It is visible as a faint smudge on a faint smudge on a moonless night, it is moonless night, it is one of the farthest one of the farthest objects visible to objects visible to the naked eye, and the naked eye, and can be seen even can be seen even from urban areas from urban areas with binocularswith binoculars

2.3 million ly away2.3 million ly away

Did You Know ?Did You Know ?

The Milky Way galaxy, and its closest The Milky Way galaxy, and its closest neighbor, the Andromeda galaxy, are neighbor, the Andromeda galaxy, are on a collision course with each other! on a collision course with each other! This collision between these two spiral This collision between these two spiral galaxies will likely occur in about 3 galaxies will likely occur in about 3 billion years, and the resulting galaxy is billion years, and the resulting galaxy is expected to be an elliptical. expected to be an elliptical.

Galaxy Classification

In 1924, Edwin Hubble divided galaxies into

different “classes” based on their appearance.

Galaxies differ in size, shape, and ages of their stars

•Hubble classification serves as the basic language of the field.

Types of GalaxiesTypes of Galaxies

Spirals & Ellipticals & Spirals & Ellipticals & IrregularsIrregulars(oh my!) (oh my!)

1. 1. Spiral GalaxySpiral Galaxy

Disk shapedDisk shaped (looks like a pinwheel) (looks like a pinwheel) Contain mixture of young/old stars Contain mixture of young/old stars

Greater concentration of stars near the Greater concentration of stars near the middle (older stars)middle (older stars)

Arms (younger stars)Arms (younger stars) are seen are seen extending from central nucleusextending from central nucleus

Orderly rotational motionOrderly rotational motion Our own Galaxy is a spiralOur own Galaxy is a spiral..

Types of Spiral GalaxiesTypes of Spiral Galaxies

Normal Spiral Normal Spiral Galaxies- Galaxies- a flattened, a flattened, rotating galaxy with rotating galaxy with pinwheel-like armspinwheel-like arms of of interstellar material interstellar material and young stars and young stars winding out from its winding out from its centercenter or nucleus or nucleus

Barred Spiral Barred Spiral Galaxies-Galaxies- a galaxy a galaxy having having straight arms straight arms extending from its extending from its centercenter Spiral arms Spiral arms attach to attach to

the bar instead of the the bar instead of the center diskcenter disk

2. 2. Elliptical GalaxiesElliptical Galaxies

(not a disk) and (not a disk) and often football shapedoften football shaped

Smooth round shapeSmooth round shape No armsNo arms Very little interstellar Very little interstellar

matter leads to matter leads to minimal star minimal star formationsformations

Composed of old Composed of old starsstars

Random star motionRandom star motion 60% of all galaxies60% of all galaxies

“Space footballs”

3. 3. Irregular GalaxiesIrregular Galaxies

No exact size or shapeNo exact size or shape Composed of mostly young starsComposed of mostly young stars Lacks symmetryLacks symmetry Small and faintSmall and faint

Final Galaxy Final Galaxy vocabulary….vocabulary….1.  Most Galaxies are 1.  Most Galaxies are

located in groups located in groups called a called a clustercluster..

2.  2.  Local GroupLocal Group – the – the name for the name for the cluster of galaxies cluster of galaxies the Milky Way is the Milky Way is inin

3.3. Super cluster Super cluster – – Gigantic Cluster Gigantic Cluster of galaxiesof galaxies

Skip QuasarsSkip Quasars

Hubble’s Tuning ForkHubble’s Tuning Forkdiagram classifying diagram classifying

different galaxies by shapedifferent galaxies by shape

Use your Hubble’s Tuning Fork Diagram to help you identify these Galaxies: