Welcome to A105 Stars and Galaxies Instructor: Caty Pilachowski Assoc. Instructor: Tara Angle Today’s APOD APOD  Read units 1, 2, 3, 4.1  Essential Facts Worksheet due Thursday

Earth Radius: 6400 km Distance from Sun: 150,000,000 km 1 AU, 8 light minutes Moon Radius: ¼ Earth’s radius Distance from Earth: 384,000 km

The Sun Radius: 700,000 km Diameter: 1,400,000 km (about 100 x the diameter of Earth) Mass: 300,000 x mass of Earth

Is Pluto a Planet? oWhat is a planet? oWhat must be considered to decide if Pluto is a planet?

Pluto – Basic Data Diameter:0.18 Earth diameters Mass0.002 Earth masses Inclination17 degrees (other planets 7 degrees or less) Eccentricity0.25 (other planets less than 0.2)

Guidance from the Discovery of Ceres 1801 Planet suspected between Mars and Jupiter Campaign organized to search the sky Ceres - the first (and largest) asteroid to be found A planet…. or not? Image from Hubble

Ceres: Not! Too small Many more asteroids found shortly thereafter Tens of thousands known today PallasJuno

What defines a planet? oRound (enough mass for strong gravity) oDominant body (tosses smaller bodies out of the Solar System) oOrbits the Sun

First News Quiz In Class QUIZ - Sept. 5 Astronomy Magazine article on Pluto: Use the “News Quiz” link on Oncourse to find the article

Who’s in the class? Freshmen? Sophomores? Juniors? Seniors? Other? School…? Major…?

Science and the Distribution Requirement  Science and technology drive much of modern life  Jobs!  Informed voters make better decisions

Why are you taking this class?

I need to take a science class and astronomy sounded easy/fun I've always been interested in astronomy I had space in my schedule for another course and thought I'd try astronomy I want to be a science teacher I'm thinking of minoring/majoring in astronomy. My friend is taking the class, so I'm taking it with her/him. This is supposed to be an easy course, and I need to bring up my GPA This course was recommended by a friend I want to amaze my friends and family with my knowledge of the night sky.

Where will we start? –The night sky –Learning to see with an astronomical eye –Size and scale Where are we going? Modern Astrophysics –A little physics –Tools –Understanding the Universe

The Nearest Stars The closest star to our Sun is Proxima Centauri, about 4 light years distant.

Most of the stars we see in the sky are within 250 light years

Our Sector of the Galaxy The Sun lies along one of our Galaxy’s spiral arms, known as the Orion Arm

View of the Milky Way Galaxy Our Milky Way galaxy contains two hundred billion stars. The Sun is about 26,000 light years from the center.

Our Milky Way Galaxy is part of a small cluster of about 3 dozen galaxies.

Virgo Supercluster Our Local Group of galaxies is part of a larger Supercluster of galaxy groups.

Galaxies and clusters of galaxies collect into vast streams, sheets, and walls of galaxies.

The Visible Universe On the largest scales, the universe seems to be more or less uniform

Put these objects in the correct order from the nearest to the farthest from Earth a)The Sun, the Milky Way, Alpha Centauri, Saturn, the Andromeda Galaxy b)The Sun, Alpha Centauri, Saturn, the Andromeda Galaxy, the Milky Way c)The Sun, Saturn, Alpha Centauri, the Milky Way, the Andromeda Galaxy d)Saturn, the Sun, Alpha Centauri, the Milky Way, the Andromeda Galaxy

Overview Organization and course goals

Course Organization  Syllabus/OncourseOncourse  Text  Assigned Reading  Lecture Notes  Written Assignments  Projects  Quizzes  Observing Office Hours Caty P.: Thursday, 11-noon SW 315 Tara Angle: Tues. 11-noon Weds. 2-3 PM SW 313

GRADES  Quizzes (100 pts)  Homework Assignments (100 pts)  Observing Activities (100 pts)  Project (100 pts)  Exams (2 x 200 pts)  Final Exam (200 pts)

Course Goals  Science as discovery  Use real astronomical data  Learn about the process of science Nova GK Per, known as the “Firework Nebula” exploded in The star lies 1500 light years away, in the direction of the constellation Perseus.

One question I’ve always had about astronomy is…

ASSIGNMENTS this week  Read units 1, 2, 3, 4.1  Essential Facts Worksheet due Thursday  1 st News Quiz next Tues.