Welcome to A105 Stars and Galaxies

Instructor: Caty Pilachowski

Assoc. Instructor: Tara Angle

Today’s APOD Read units 1, 2, 3, 4.1

Essential Facts Worksheet due Thursday

Earth Radius: 6400 kmDistance from Sun: 150,000,000 km

1 AU, 8 light minutes

MoonRadius: ¼ Earth’s radiusDistance from Earth:

384,000 km

TheSun

Radius: 700,000 kmDiameter: 1,400,000 km

(about 100 x the diameter of Earth)

Mass: 300,000 x mass of Earth

Is Pluto a Planet?

o What is a planet?

o What must be considered to decide if Pluto is a planet?

Pluto – Basic Data• Diameter: 0.18 Earth

diameters• Mass 0.002 Earth masses

• Inclination 17 degrees(other planets 7 degrees or less)

• Eccentricity 0.25(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

Pallas Juno

What defines a planet?

o Round (enough mass for strong gravity)

o Dominant body (tosses smaller bodies out of the Solar System)

o Orbits the Sun

First News Quiz

• In Class QUIZ - Sept. 5• Astronomy Magazine article on

Pluto:www.astronomy.com/asy/default.aspx?c=a&id

=4474 

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?

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 theMilky 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 Superclust

er

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/Oncourse

Text Assigned

ReadingLecture NotesWritten

AssignmentsProjectsQuizzesObserving

Office Hours

Caty P.: Thursday, 11-noonSW 315

Tara Angle: Tues. 11-noonWeds. 2-3 PMSW 313

GRADESQuizzes (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 1901. The star lies 1500 light years away, in the direction of

the constellation Perseus.

One question I’ve always had about astronomy is…

ASSIGNMENTSthis week

Read units 1, 2, 3, 4.1Essential Facts Worksheet

due Thursday1st News Quiz next Tues.