Download Chapter 1 - A Modern View of the Universe

Welcome to AY 101 – S002
Introduction to Astronomy
Professor: Dr. Jimmy Irwin
Meeting Room: Gallalee Hall 227
Class time: MWF 11:00-11:50
Course website:
http://www.astr.ua.edu/jairwin/AY101/AY101.html
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 for a homework account on Mastering
Astronomy (accessible through Blackboard).
Homework
The access code for Mastering Astronomy is
bundled with your textbook, or can be bought
online.
From Blackboard, click on "Mastering
Astronomy Course Home to receive create an
account on Mastering Astronomy.
Do this as soon as you can, as your first
homework assignment designed to get you
comfortable with the Mastering Astronomy
interface will be assigned on Wednesday.
Chapter 1
A Modern View of the Universe
Planet
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 / Satellite
A rocky or icy
object which
orbits a planet.
Asteroid
A relatively small
and rocky/metal
object which orbits
a star.
Comet
A relatively
small and
primarily icy
object which
orbits a star.
Star
~106 (1 million) km diameter
light crossing time: 3 seconds
Hot, gaseous objects
generating heat and
energy by fusing
hydrogen to helium in
their cores
Solar (Star) System
A star and all the material that orbits it, including its
planets and moons, asteroids, comets
Light crossing time: 8 hours
(Earth-Sun: 8.3 minutes)
1010 km
Nebula
An interstellar cloud
~10 light years = 1014 km
of gas within galaxies
Star Cluster
A collection of dozens
to millions of stars
gravitationally bound
(or not) orbiting (or
inside) a galaxy.
Open cluster
10 light years = 1014 km
Globular Cluster
Galaxy
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
A collection of tens to
thousands of galaxies
gravitationally bound.
10 million light
years across
= 1020 km
Universe
All matter and energy.
Everything within and
between galaxies.
An estimated 100
billion galaxies in the
observable Universe
1010 (10 billion) light
years = 1023 km
Where does Earth fit into the Universe?
Our Very, Very Ordinary
Location
Earth – an average size planet in an
average-sized orbit
The Sun – a slightly above-average size
star, just one of 100 billion in our Galaxy
Our location in the Milky Way Galaxy –
neither near the center nor near the
outskirts
Our Galaxy – neither unusually big nor
small, just one of 100 billion
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
Wednesday!
Participation grading will start for real on
Wednesday, so register your clickers
beforehand, and bring them on Wednesday.
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 6digit 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 button
Step 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
Distance Units and Astronomy
Planets: kilometers (km) (1 km ~ 0.6 mile)
- 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?
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?
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?
Light travels at a finite speed (300,000 km/s).
Destination
Light travel time
Moon
1 second
Sun
8 minutes
Nearest star
4.3 years
Andromeda Galaxy
2.5 million years
Thus, we see objects as they were in the past:
The farther away we look in distance,
the further back we look in time.
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.
© 2015 Pearson
Education, Inc.
How large is the Solar System?
Let’s shrink everything down by a factor of 10 billion!
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 tip of a ball point pen
How large
is the Solar
System?
If the Sun is
a grapefruit,
Neptune is a
small pebble
located
somewhere
3 blocks
away!
How Large is the Solar System?
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!
Wrong!
Our Solar System is
almost entirely empty
space!
How Far Away is the Nearest Star
on This Same Spatial Scale?
How far away is the nearest star (if the
Sun is the size of a grapefruit in
Washington DC)?
A) 20 blocks
B) 5 miles
C) 50 miles
D) in California
Full credit (2/2) for all who answer.
How far away is the nearest star (if the
Sun is the size of a grapefruit in
Washington DC)?
A) 20 blocks
B) 5 miles
C) 50 miles
D) in California
Full credit (2/2) for all who answer.
Nearest Star at Distance of San Francisco!
Actual distance: 4.3 light years
Galaxy
Galaxy
If stars are so sparsely spaced, then why
do galaxies look like this?
Galaxy
Galaxy
Galaxies are
mostly empty
space
(neglecting
diffuse gas
they contain)!
Answer: Our telescopes are unable to
resolve the actual size of all the stars – we
see a blur of many, many faint stars.
How large is the Galaxy?
Sun
Pluto
590m
Neptune Uranus
450m
287m
Earth Venus
15m
11m
Mercury
6m
How far from Sun to nearest star?
Let’s shrink the Universe by another factor of 1 billion
1:1019 (10 quintillion!) scale – equivalent to the Milky Way Galaxy being as big as
a football field. Sun is now the size of an atom.
How far away is the nearest star (if the
Milky Way Galaxy is the size of a
football stadium and the Sun is at the
25 yard line)?
A) 4 millimeters away
B) 1 foot away
C) 17 yard line
D) the nearest end zone
Full credit (2/2) for all who answer.
How far away is the nearest star (if the
Milky Way Galaxy is the size of a
football stadium and the Sun is at the
25 yard line)?
A) 4 millimeters away
B) 1 foot away
C) 17 yard line
D) the nearest end zone
Full credit (2/2) for all who answer.