Stars and GalaxiesStars and Galaxies

What are we going to cover?What are we going to cover?

Our Place in the UniverseThe Electromagnetic SpectrumClassifying StarsClassifying GalaxiesHistory of the Universe

First up…First up…

Our Place in the UniverseWhat is our Universe made of?How big are things? How far away?How do we know?

Examining the ComponentsExamining the Components

Stars Gas and dust (Nebulae)Star clustersGalaxies

Different types of stars

Different types of stars

Image from http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/2003/21/image/a/results/50/

Types of StarsTypes of Stars

Big (Super massive)Small (Dwarf)RedBlueYellowIn groups (Clusters)Alone (Rogue)

More later

What is a “star cluster”?What is a “star cluster”?

stars formed together at same time

stars may be gravitationally bound together

two types: open (galactic) and globular

Image at http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/2007/18/image/a/format/web/results/50/

Open ClustersOpen Clusters

dozens to thousands of starsyoung stars! only a few

million years oldmay still be surrounded by

nebula from which they formedlocated in the spiral arms of a

galaxyexample: Pleiades

Image at http://hubblesite.org/newscenter/archive/releases/star%20cluster/open/2004/20/image/a/results/50/

More open star clustersMore open star clusters

Image from http://hubblesite.org/newscenter/archive/releases/star%20cluster/open/2006/17/image/a/results/50/

Globular ClustersGlobular Clusters

millions to hundreds of millions of stars

old! 6 to 13 billion years mostly red giants and dwarfs stars are clumped closely together,

especially near the center of the cluster (densely)

surround our disk as a halo

Image at http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/1999/26/image/a/results/50/

What is a “nebula”?What is a “nebula”?

A cloud in spaceMade of gas and dust

Can have stars inside

Most of the ones we see are inside our Milky Way Galaxy

Different types

Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/

Large, massive, bright nebulaeLarge, massive, bright nebulae

Emission Nebula• The hot gas is emitting light

Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/

Colder, darker nebulaeColder, darker nebulae

Dark dust blocking the hot gas behind it

NOAO/AURA/NSF Image from http://hubblesite.org/newscenter/archive/releases/nebula/dark/2001/12/image/c/results/50/

Leftovers from an ExplosionLeftovers from an Explosion

Supernova remnant (smaller, less gas)

Image at http://hubblesite.org/newscenter/archive/releases/nebula/supernova-remnant/2005/37/results/50/

What is a “galaxy”?What is a “galaxy”?

A large group of stars outside of our own Milky WayMade of billions to trillions of stars

Also may have gas and dust

Spiral, or elliptical, or irregular shapedImage at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2007/41/results/50/

Spiral galaxy--AndromedaSpiral galaxy--Andromeda

NOAO/AURA/NSF Images at http://www.noao.edu/image_gallery/html/im0606.html and http://www.noao.edu/image_gallery/html/im0685.html

Elliptical GalaxiesElliptical Galaxies

Images at http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/2007/08/image/a/format/large_web/results/50/ and http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/1995/07/results/50/

Irregular GalaxiesIrregular Galaxies

NASA and NOAO/AURA/NSF Images at http://hubblesite.org/newscenter/archive/releases/galaxy/irregular/2005/09/results/50/ , http://www.noao.edu/image_gallery/html/im0560.html , and http://www.noao.edu/image_gallery/html/im0993.html

20© 2004 Astronomical Society of the Pacific www.astrosociety.org

How big is the Milky Way Galaxy?How big is the Milky Way Galaxy?

100,000 light years

Image credits: NASA, STScI

Our Galaxy: the Milky WayOur Galaxy: the Milky Way

has about 200 billion stars, and lots of gas and dust

is a barred-spiral (we think)about 100,000 light-years wideour Sun is halfway to the edge, revolving at

half a million miles per hour around the center of the Galaxy

takes our Solar System about 200 million years to revolve once around our galaxy

The Milky WayThe Milky Way

Image at http://news.nationalgeographic.com/news/bigphotos/1945371.html

Mapping the Milky WayMapping the Milky Way

We can see stars star clusters nebulae Galaxies

Let’s try to Map our Galaxy

How do we know what our Galaxy looks like?

Measuring DistancesMeasuring Distances

What is a Light Year? A light year is the distance light travels in a year. Light moves at a

velocity of about 300,000 kilometers (km) each second; how far would it move in a year?

About 10 trillion km (or about 6 trillion miles).

Why do we use light years? Show me how far 5 centimeters is. Now show me 50 centimeters. Now tell me (without thinking about it, or calculating it in meters) how far

500 centemeters is. 2000? 20,000? We need numbers that make sense to us in relationship to objects; we

scale up and use meters and kilometers for large numbers.