Ch1 Scale - UCF Physics

AST 2002
Introduction to Astronomy
• Textbook
– The Essential Cosmic Perspective, by
– Included with your textbook should be an
access package for MasteringAstronomy
• Your Professor
– Dr. Dan Britt
– Office is PSB 442
– Office hours are
• T Th 9:30-10:20 AM
• 3 exams (80% of grade)
– The first two exams will cover 1/3 of the course each
– The final is will be comprehensive with extra emphsis on
the last 1/3 of the course.
• Quizzes (10%)
– I will give brief in-class quizzes on the book material every
– It will cover the material to be discussed. Read the book in
• Readings (10%)
– There are 12 short articles assigned.
– We will discuss each in class and you will be graded on
your participation.
• Scores will be posted on MyUCF Grades.
• I am not here to read you the book
– I am what is called an “expert”
– There are lots of important things that I think you
NEED TO KNOW are NOT in the book….they will be
in the lectures
• I will post the powerpoints I use
– BUT….This is NOT an on-line class
– Almost every class will have a section that is NOT in
the Book and will NOT be put in the on-line
powerpoints….but will be on the tests.
– There is no substitute for coming to class
Extra Credit
• Attend an observing session at the Robinson
Observatory AND write up an Observing Report of
what you have seen: 2% extra
– Observing report forms will be available at the Observatory
– YOU MUST turn in your observing report at the Observatory,
NO forms will be accepted in class.
• This extra 2% usually moves someone a grade
• Observatory schedule is posted
– Extra credit must be completed before April 15, so go early!
Robinson Observatory
• Watch the posted schedule for dates
• Time: Is listed OR when it gets
• Clouds? IF it is cloudy….Robinson will
be closed.
• Standing in the rain at Robinson does
NOT constitute extra credit.
How to Get an “A”
• Attend class!
– People who blow off the lectures don’t do very
well….figure 30% of test questions will NOT be
from the book or posted slides
• Participate in Class
– 10% of your grade will be participation and
– I will give extra points for good questions and
• Read the book!
– Quizzes will be in advance of the lectures
• DO the extra credit!
Dr. Britt’s quirks
• This is a small class….discussion will
be key!
• I ask questions…..
– Correct answers get points.
• I invite you to ask questions.
– You do get points for good questions….
• One more thing……
– I am on various NASA review and advisory
panels, so I will be gone sometimes.
– I also have to attend scientific meetings.
– You will have guest lecturers.
Lets do a little front-porch science…
What can you tell about the history
and composition of the Moon just
from what you can see from your
What do you see?
What do you see?
Dark Stuff
Light Stuff
What can you tell me about the
Light Stuff?
Light Stuff
What can you tell me about the
Light Stuff?
• It’s lighter
• It has more
• It covers more
of the surface
Light Stuff
What can you tell me about the
Dark Stuff?
Dark Stuff
What can you tell me about the
Dark Stuff?
• It’s darker
• It has fewer
Dark Stuff
• It covers less
of the surface
What does having more
craters mean?
So the light stuff is older….
How did the dark stuff get
where it is?
Let’s recap what we know
• The Moon has Dark Stuff and Light
• The Light Stuff is….
– Lighter, has more craters, and is older
• The Dark Stuff is….
– Darker, has fewer craters, and is
• What does this mean for the history
of the Moon?
So….what can we KNOW about
the Moon from a few simple
• It has two major regions
• Those regions were created at MUCH
different times
• The older Light Stuff was subjected to
EXTREMELY heavy cratering
• The younger Dark Stuff appears to have
flowed over the low-lying Light Stuff
– The Dark Stuff was once molten and probably
like terrestrial basalt (lava).
Not bad for an evening spent
on the porch….
• A few simple observations can tell
you a great deal about an object.
• To know more took sending humans
to the Moon.
So…..where would you send
Humans on the Moon?
But, the engineers have a few constraints:
1. Can’t land north or south of these lines
2. Can’t land on anything rough
12 14
Landing Sites
Astronomy is…..
• In this class Astronomy means a
whole lot more than looking through
• Astronomy is really about how the
Universe is put together
– How it was created
– How it evolves
– Why there are planets
– How Earth fits in the scheme of things
Where do we come from?
• The first (and simplest) atoms were created
during the Big Bang.
• More complex atoms were created in stars.
• When the star dies, they are expelled into
space…. to form new stars and planets!
Most of the atoms in
our bodies were
created in the core
of a star!
Looking back in time
• Light, although fast, travels at a finite speed.
• It takes:
– 8 minutes to reach us from the Sun
– 8 years to reach us from Sirius (8 light-years away)
– 1,500 years to reach us from the Orion Nebula
• The farther out we look into the Universe, the farther back in
time we see!
A Sense of Scale
• The first difficult concept is the immensity of
time and space
• What we will be doing a lot of is stepping out of
human scale
• Astronomers talk about large numbers in
powers of ten…..
– This is just a shorthand for writing large numbers
– For example the distance to the Sun is 150 million
Kilometers (150,000,000 Km) or 1.5 x 108 Km
• The planets outside the Air and Space Museum in DC
(1:10 billion)
• Our Sun is the size of a grapefruit, Jupiter the size of a
• At this scale the nearest star would be another
grapefruit in San Francisco
100 (1 meter)
101 (10 meters)
102 (100 meters)
103 (1000 meters)
104 (10,000 meters)
105 (100,000 meters)
106 (1,000,000 meters)
108 (100,000,000 meters)
1010 (10,000,000,000 meters)
1012 (1,000,000,000,000 meters)
1013 (10,000,000,000,000 meters)
1020 (100,000,000,000,
000,000,000 meters)
1022 (10,000,000,000,000,
000,000,000 meters)
10 (100,000,000,000,000,
000,000,000,000 meters)
Aldebaran translates as "the follower", because
this star appears to follow the Pleiades
How big is the Universe?
• The Milky Way is one of about 100 billion galaxies.
• 1011 stars/galaxy x 1011 galaxies = 1022 stars
As many stars as grains of (dry) sand on all Earth’s beaches…