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A105
Stars and Galaxies
Essential Facts Worksheet due today
First News Quiz on Sept. 5
Read units 5, 6, 10 for next week
Course
Organization
Syllabus/Oncourse
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
How will the class work?
News Quiz every Tuesday
best 10 of 13
Homework every Thursday
best 10 of 13
Project due Nov. 30
4 observing activities (required)
Exams Sept. 28 and Nov. 2
Final exam Dec. 12
First News Quiz
• In Class QUIZ - Sept. 5
• Astronomy Magazine article on Pluto:
• Use the “News Quiz” link on
Oncourse to find the article
A copy of the textbook is on 2-hour reserve in
the Swain West Library (2nd floor of this bldg.)
The Sun Today
Solar
Orbiting
Heliospheric
Observatory
(SOHO)
Orbits between the Sun and
Earth, about a million miles away
– a constant view of the Sun
Another view from Soho
• View of
Mercury from
the Solar
Orbiting
Heliospheric
Observatory
satellite
Mercury
Regulus
Review Scientific Notation
 Write and work with very large or small numbers
without so many digits.
 Only one digit should be in front of the decimal.
 The exponent positive when the number is greater
than one, negative when the number is less than
one.
43,000,000. = 4.3 x 107
0.000043 = 4.3 x 10-5
Use the worksheet with the first homework for practice
Powers of 10
Power of 10
billion
million
thousand
hundredth
thousandth
millionth
billionth
Notation
Prefix
Abbr.
109
106
103
10-2
10-3
10-6
10-9
“giga”
“mega”
“kilo”
“centi”
“milli”
“micro”
“nano”
G
M
k
c
m
m
n
Basic
Definitions
Mass
Earth masses
Solar masses
Distances
Solar Radius (700,000 km)
Astronomical Unit (AU)
Light year
Speed
Speed of light
(300,000 km per second)
What is an Astronomical Unit?
• The average distance between the
Earth and Sun
– 150,000,000 km = 1.5 x 108 km
– 93,000,000 miles = 9.3 x 107 miles
– 8 LIGHT MINUTES
Approximation
• Some numbers are know very
accurately, but some are NOT
• Use an appropriate number of digits
• We will use approximate numbers
What is a Light
Year?
The speed of light is
300,000 km/second
a light year is a distance!
a light year is the distance that light can
travel in one year
light can travel about 10 trillion km
(10,000,000,000,000 km) in one year
Basic Definitions
Objects
• Star
• Planet
• moon, satellite,
asteroid, comet
• Nebula
Collections
• Solar system
• Star System
• Galaxy
• Cluster or group of
galaxies
• Supercluster
• Universe
• Observable universe
The star Betelgeuse is about 500 light
years away from us in the constellation
Orion. If this star exploded right now, how
long would it be until we found out about it?
a)
b)
c)
d)
e)
almost immediately
8 minutes
10 years
500 years
500 light years
Size and Scale
know those essential
facts!
Beyond the
Milky Way
Using those essential facts!
Which of the following diagrams most
closely depicts the relative sizes and
distance between Earth and the
Moon?
Modern science relies on
observations and experiments!
Understanding Science
Purpose – to understand the universe
well enough to figure out the basic
relationships that govern it
A process for understanding and
predicting
What about facts?
will it rain tomorrow?
what will be on the quiz?
what will happen if…?
new discoveries
better data
new theories
facts change!
The
Science
of
Astronomy
Refine the
model
Learn what is known
and what is NOT
known…
Develop a model to
explain or describe
what is known
Use the model to
predict what is not
known
TEST the predictions
But science rarely proceeds in
this idealized way… For
example:
• Sometimes we start by “just looking”
then coming up with possible
explanations.
• Sometimes we follow our intuition
rather than a particular line of
evidence.
Testing the Predictions
Experiments and Observations
repeatable
quantitative
well defined
fair
Statistics evaluate the reliability of
observations
Examples
 What time is it?
 Heads or tails?
Laws and Theories (and models)
A law is a set of hypotheses that explains
WHAT is happening – usually mathematical
Kepler’s laws of planetary motion
A theory is a well-developed set of
hypotheses that explains why many related
natural phenomena happen
Einstein’s Theory of General Relativity
Laws and theories are both based on
detailed and repeatable observations and
measurements
Laws and theories both yield testable
predictions
What is a scientific theory?
• The word theory has a different meaning in
science than in everyday life.
• In science, a theory is NOT the same as a
hypothesis, rather:
• A scientific theory must:
—Explain a wide variety of observations with a
few simple principles, AND
—Must be supported by a large, compelling body
of evidence.
—Must NOT have failed any crucial test of its
validity.
Is a Theory Right?
Can’t ever “prove” a theory right
Does the theory make correct
predictions?
If it doesn’t, then it’s wrong
If it’s not tested or testable, it’s
NOT a scientific theory
Burden of proof is on the person
making the claim
“Extraordinary claims require
extraordinary proof” (Sagan)
Understanding Science
Purpose – to understand the universe
well enough to figure out the basic
relationships that govern it
A process for understanding and
predicting
What about facts?
will it rain tomorrow?
what will be on the quiz?
what will happen if…?
new discoveries
better data
new theories
facts change!
An Ongoing Process
The process of science has been
so successful because
results are widely shared and
evaluated
experiments are reproduced and
checked
value of ideas based on observation
and usefulness, not authority
Criteria of Science
•
•
•
•
•
•
Consistent
Observable
Natural
Predictable
Testable
Tentative
Tentative:
Consistent:
Observable:
Natural:
Predictable:
Testable:
A Science
The
results
event
natural
is
The
Predictions
subject
natural
under
of
caused
to
repeated
must
study
observations
can
must
revision
cause
be
testable
bebe
can
observed
and
used
be or
to or
experiment
natural
explain
correction
used towhy
through
evidence
make
based
are
or
more
must
how
on
specific
observations
new
the
be
or less
event
available.
the
or
same.
happens
observations
predictions.
experiments.
Debating Scientific Issues
How do we tell who is correct?
Majority vs. minority opinions
Majority isn’t always right
Debate is a poor technique for deciding
EVIDENCE and DATA
How was the experiment done?
Was it repeated by others
Is a new theory TESTABLE?
How can we
distinguish
science from
non-science?
• Defining science can be surprisingly difficult
• Science from the Latin scientia, meaning
“knowledge”
• But not all knowledge comes from science…
Warning Signs of Bad Science
How is it announced? Is the source reliable?
How good is the evidence?
is it anecdotal? does it appeal to authority?
does it fit what you already know?
does it violate widely-accepted laws or theories?
is contrary evidence ignored?
What kind of reasoning is used?
Can the claim be tested?
The Baloney Detection Collection
Phil Plait's Bad Astronomy: Home Page
PLANET-DISSOLVING DUST CLOUD
IS HEADED TOWARD EARTH!
September 12, 2005, by Yahoo! News
•
By MIKE FOSTER
CAMBRIDGE, Mass. -- Scared-stiff astronomers have detected a mysterious
mass they've dubbed a "chaos cloud" that dissolves everything in its path,
including comets, asteroids, planets and entire stars -- and it's headed
directly toward Earth!
Discovered April 6 by NASA's Chandra X-ray Observatory, the swirling, 10
million-mile- wide cosmic dust cloud has been likened to an "acid nebula" and is
hurtling toward us at close to the speed of light -- making its estimated time
of arrival 9:15 a.m. EDT on June 1, 2014. The bad news is that the total
annihilation of our solar system is imminent.
To avoid widespread panic, NASA has declined to make the alarming discovery
public. But Dr. Sherwinski's contacts at the agency's Chandra X-ray
Observatory leaked to him striking images of the newly discovered chaos
cloud obliterating a large asteroid.
“If it continues unchecked, the chaos cloud will eventually reduce our galaxy
to the state of absolute chaos that existed before the birth of the universe,”
the astrophysicist warned.
Assignments for next week:
Read units 5, 6, 10
News Quiz on Tues., Sept. 5
Moon worksheet due next Thursday