Stars and Galaxies

What are we going to cover?  Our Place in the Universe  The Electromagnetic Spectrum  Classifying Stars  Classifying Galaxies  History of the Universe

First up…  Our Place in the Universe  What is our Universe made of?  How big are things? How far away?  How do we know?

Examining the Components  Stars  Gas and dust (Nebulae)  Star clusters  Galaxies

Different types of stars Image from

Types of Stars  Big (Super massive)  Small (Dwarf)  Red  Blue  Yellow  In groups (Clusters)  Alone (Rogue)  More later

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

Open Clusters   dozens to thousands of stars   young stars! only a few million years old   may still be surrounded by nebula from which they formed   located in the spiral arms of a galaxy   example: Pleiades Image at

More open star clusters Image from

Globular 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

What is a “nebula”?  A cloud in space  Made 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

Large, massive, bright nebulae Emission Nebula The hot gas is emitting lightThe hot gas is emitting light Orion image at

Colder, darker nebulae Dark dust blocking the hot gas behind it NOAO/AURA/NSF Image from

Leftovers from an Explosion Supernova remnant (smaller, less gas) Image at

What is a “galaxy”?  A large group of stars outside of our own Milky Way  Made of billions to trillions of stars  Also may have gas and dust  Spiral, or elliptical, or irregular shaped Image at

Spiral galaxy--Andromeda NOAO/AURA/NSF Images at and

Elliptical Galaxies Images at and

Irregular Galaxies NASA and NOAO/AURA/NSF Images at and

20 How big is the Milky Way Galaxy? 100,000 light years Image credits: NASA, STScI

Our 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 wide   our 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 Way Image at

Mapping 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 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.