Welcome to AY 101 – S004

Professor: Dr. Jimmy IrwinMeeting Room: Gallalee Hall 227Class time: MWF 11:00-11:50 Course website: http://www.astr.ua.edu/jairwin/AY101/AY101.html

Introduction to Astronomy

Reminder

Class notes are available after each class on the course webpage

http://www.astr.ua.edu/jairwin/AY101/AY101.html

Audio recordings of classes also available on Tegrity.

Also, register on masteringastronomy.com

HomeworkHomework The access code for Mastering Astronomy is bundled

with your textbook, or can be bought online.

From Blackboard, click on "MasteringAstronomy.com instructions") to receive instructions on setting up an account on Mastering Astronomy.

The course ID for this class is: IRWINAY101F2015

Do this as soon as you can, as a practice (ungraded but mandatory) homework assignment designed to get you comfortable with the MasteringAstronomy.com interface will be assigned on Monday.

The access code for Mastering Astronomy is bundled with your textbook, or can be bought online.

From Blackboard, click on "MasteringAstronomy.com instructions") to receive instructions on setting up an account on Mastering Astronomy.

The course ID for this class is: IRWINAY101F2015

Do this as soon as you can, as a practice (ungraded but mandatory) homework assignment designed to get you comfortable with the MasteringAstronomy.com interface will be assigned on Monday.

Chapter 1Our Place in the Universe

Chapter 1Our Place in the Universe

PlanetPlanet

A moderately large object which orbits a star; it shines by reflected optical light from its host star. Planets may be rocky or gaseous in composition.

A moderately large object which orbits a star; it shines by reflected optical light from its host star. Planets may be rocky or gaseous in composition.

Moon / SatelliteMoon / Satellite

A rocky or icy object which orbits a planet.

A rocky or icy object which orbits a planet.

AsteroidAsteroid

A relatively small and rocky object which orbits a star.

A relatively small and rocky object which orbits a star.

CometComet

A relatively small and icy object which orbits a star.

A relatively small and icy object which orbits a star.

~106 (1 million) km diameter

light crossing time: 3 seconds

~106 (1 million) km diameter

light crossing time: 3 seconds

StarStar

Hot, gaseous objects generating heat and energy by fusing hydrogen to helium in their cores

Solar (Star) SystemSolar (Star) SystemA star and all the material that orbits it, including its planets and moons

Light crossing time: 10 hours

(Earth-Sun: 8.3 minutes)

A star and all the material that orbits it, including its planets and moons

Light crossing time: 10 hours

(Earth-Sun: 8.3 minutes)

1010 km

NebulaNebula

An interstellar cloudof gas within galaxiesAn interstellar cloudof gas within galaxies ~10 light years = 1014 km

Star ClusterStar Cluster A collection of dozens to

millions of stars gravitationally bound (or not) orbiting (or inside) a galaxy.

A collection of dozens to millions of stars gravitationally bound (or not) orbiting (or inside) a galaxy.

10 light years = 1014 km

Open cluster Globular Cluster

GalaxyGalaxy A great island of billions

of stars and gas, all held together by gravity and orbiting a common center

A great island of billions of stars and gas, all held together by gravity and orbiting a common center

100,000 light years across = 1018 km

Galaxy Groups or Clusters

Galaxy Groups or Clusters

A collection of tens to thousands of galaxies gravitationally bound.

A collection of tens to thousands of galaxies gravitationally bound.

10 million light years across = 1020 km

UniverseUniverse

All matter and energy. Everything within and between galaxies.

1010 (10 billion) light years = 1023 km

Where does Earth fit into the Universe?

Where does Earth fit into the Universe?

Our Very, Very Ordinary Location

Our Very, Very Ordinary Location

Earth – an average size planet in an average-sized orbit

The Sun – a slightly above-average size star

Our location in the Milky Way Galaxy – neither near the center nor near the outskirts

Our Galaxy – neither unusually big nor small

Earth – an average size planet in an average-sized orbit

The Sun – a slightly above-average size star

Our location in the Milky Way Galaxy – neither near the center nor near the outskirts

Our Galaxy – neither unusually big nor small

Earth/Moon viewed from 183 million km (114 million miles), about 1.2 Earth-Sun distances by MESSENGER spacecraft.

Launch: August 3, 2004

Arrived at Mercury: March 18, 2011

Earth viewed by Voyager 1, 4 billion miles or 6.4 billion kilometers away

Don’t Forget Clickers on Monday!

Don’t Forget Clickers on Monday!

Participation grading will start for real on Monday, so register your clickers beforehand, and bring them on Monday.

If you brought your clickers today, you will get a day’s worth of extra credit added to your participation grade.

Participation grading will start for real on Monday, so register your clickers beforehand, and bring them on Monday.

If you brought your clickers today, you will get a day’s worth of extra credit added to your participation grade.

Clickers:

You will need to register your clickers by going to your Blackboard page for this course and clicking on “Register Clickers Here”, and inputting the 6-digit code after the words: Device ID (some of the digits are letters) on the back of the clicker device.

Clickers:

Step 1: Press the Channel buttonStep 2: Type in “12” (will always be 12 for this course)Step 3: Hit “Enter”Step 4: When question is asked, hit “A”, “B”, “C”, etc. button

Question:

The most interesting finding from the recent New Horizons fly-by of Pluto is:

A) the curious lack of craters on Pluto.

B) the heart-shaped feature on Pluto.

C) the different colors of Pluto and its moon

Charon.

D) Why are we talking about Mickey Mouse’s

dog?

The Length Scale of the Universe

The Length Scale of the Universe

Distance Units and Astronomy

Distance Units and Astronomy

Planets: kilometers (km) - i.e., Earth’s circumference is ~40,000 km

Solar System: Astronomical Unit (AU) - average Earth-Sun distance = 150 million

km - Venus is 0.7 AU from Sun, Mars at 1.5 AU

Stars, Galaxies, Universe: light year (ly) - 9.46 trillion km (distance light travels in

one year)

Planets: kilometers (km) - i.e., Earth’s circumference is ~40,000 km

Solar System: Astronomical Unit (AU) - average Earth-Sun distance = 150 million

km - Venus is 0.7 AU from Sun, Mars at 1.5 AU

Stars, Galaxies, Universe: light year (ly) - 9.46 trillion km (distance light travels in

one year)

How far is a light-year?How far is a light-year?

1 light-year = (speed of light) (1 year)

km 365 days 24 hr 60 min 60 s= 300,000

s 1 yr 1 day 1 hr 1 min

×

⎛ ⎞⎛ ⎞× × × ×⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

How far is a light-year?How far is a light-year?

1 light-year = (speed of light) (1 year)

km 365 days 24 hr 60 min 60 s= 300,000

s 1 yr 1 day 1 hr 1 min

=9,460,000,000,000 km

×

⎛ ⎞⎛ ⎞× × × ×⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

A light-year (or parsec, where 1 parsec = 3.26 light years) is a unit of distance, not a unit of time (sorry, Han Solo!).

"You've never heard of the Millennium Falcon?... It's the ship that made the Kessel Run in less than twelve parsecs."

How can we know what the universe was like in the past?

How can we know what the universe was like in the past?

Light travels at a finite speed (300,000 km/s).

Thus, we see objects as they were in the past:The farther away we look in distance,

the further back we look in time.

Light travels at a finite speed (300,000 km/s).

Thus, we see objects as they were in the past:The farther away we look in distance,

the further back we look in time.

Destination Light travel time

Moon 1 second

Sun 8 minutes

Sirius 8 years

Andromeda Galaxy 2.5 million years

This part of the image is 100,000 years older

than this part!

At great distances, we see objects as they were when the universe was much younger. Appearance of object is effectively “frozen in time” while the light from the object is transiting space.

At great distances, we see objects as they were when the universe was much younger. Appearance of object is effectively “frozen in time” while the light from the object is transiting space.

© 2015 Pearson Education, Inc.

How large is the solar system?

How large is the solar system?

1:10 billion (1010) scale - the Sun is the size of a grapefruit - Jupiter is the size of a marble - Earth is the size of a ball point

Let’s shrink everything down by a factor of 10 billion!

How large is

the Solar System?

How large is

the Solar System?

How Large is the Solar System?

How Large is the Solar System?

Wrong!

Children’s books often give us the wrong impression of how large planets are relative to their distances.

If the Sun is a grapefruit, Neptune is a small pebble located somewhere 3 blocks away!

Our Solar System is almost entirely empty space!