Stars and Galaxies
Dec 16, 2015
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?
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.