Phys 1533 Descriptive Astronomy
Instructor: Dr. Jackie Dunn
Required texts:
1. Astronomy: A Beginner’s Guide to the
Universe, 5th ed by Chaisson & McMillan
2. Lecture Tutorials for Introductory Astronomy,
2nd ed by Prather, Slater, Adams, &
Brissenden -- BRING THIS TO CLASS
EVERYDAY!
A Little About Me
• Assistant Professor of Physics
• Ph.D. in astrophysics from Texas
Christian University (Fort Worth, TX)
• Office: McCoy Hall, room 219D
• Email: jackie.dunn@mwsu.edu
• Phone: (940) 397-4184
Course Structure
•
•
•
•
Lecture
Think-Pair-Share Questions
Lecture Tutorials
Open Discussions
How do we learn?
• By doing!
• Just listening to lecture is not enough.
Education Research
• Students retain about 10% what they
here in pure lecture-style courses.
• At the University of Arizona, students
took a 68 question test:
– Scored 30% pre-course.
– Scored 50% post-lecture.
– Scored 75% post-lecture tutorials.
Grading
•
•
•
•
•
Semester Project: 15%
Labs: 15%
Participation: 10%
2 Exams: 20% each (40% total)
Final Exam: 20% (Yes, it’s cumulative.)
Grading Participation
• There will be in-class activities nearly
every class period.
• These will occasionally be collected.
• Grading scale:
– 80% participation points: 10 pts
– 70 to 79% participation points: 8 pts
– 60 to 69% participation points: 6 pts
– 50 to 59% participation points: 4 pts
– 40 to 49% participation points: 2 pts
– Below 40%: 0 pts
Think-Pair-Share Example
Using your letter cards (and without
discussing with anyone), determine how
to represent the two answer choices: (1)
“E” and (2) “I have no idea.”
What is astronomy?
• The study of the universe.
• It involves concepts from physics and
math, as well as from chemistry,
geology, and biology.
• It is NOT about making predictions
about people’s lives (that would be
astrology, which is NOT based on
science).
Has the study of astronomy
had an impact on your day-today
life?
(a)
(b) No
Yes
Any particular topics you would like
to cover this semester?
A Little Perspective
The above image is a
zoomed in version of
one of the darkest
regions in the image to
the left.
Our Place in Space
• Planet (Earth)
• Star (Sun)
• Galaxy (Milky Way) - Gravitationally bound
grouping of a large number of stars.
• Universe (everything) - The universe includes
everything in existence. There are billions of
galaxies.
Constellations in the Sky
• On any night, you can see some 3000 stars with the
unaided eye.
• People tend to see patterns (your eyes and brain like
to connect the dots). This human habit has given us
the constellations.
• Northern hemisphere: named after mythological
heroes and animals.
• Southern hemisphere: named by northern explorers
when they traveled south.
• There are 88 named constellations in all.
A Couple Constellations
Leo, the Lion
Ursa Major, the Great Bear
The Celestial Sphere
• Ancient observers deemed the stars to be
fixed to a sphere that rotated around the
earth - we call this the celestial sphere.
• Ancient astronomers thought the stars
moved, but now we know the apparent
motion of the stars is caused by the earth’s
rotation.
Celestial Coordinates
• Declination (latitude)
• Right Ascension (longitude)
Is the horizon shown a real
physical horizon, or an
imaginary plane that extends
from the observer and Earth
out to the stars?
Celestial Sphere Rotation
Star B
2
Star A
1
2
Celestial Sphere
Can the observer shown see
an object located below the
horizon?
Celestial Sphere
3
1
4
3
Is there a star that is in an
unobservable position?
When a star travels from
being below the observer’s
horizon to being above the
observer’s horizon, is that star
rising or setting?
4
Celestial Sphere
Rotation
Figure 2
Horizon
Tutorial: Position (p. 1)
• Work with a partner.
• Read the instructions and questions carefully.
• Talk to each other and discuss your answers
with each another.
• Come to a consensus answer you both agree
on.
• If you get stuck or are not sure of your answer
ask another group.
• If you get really stuck or don’t understand
what the Lecture Tutorial is asking, ask me
for clarification.
In what
direction is the
observer
facing?
Celestial Sphere Rotation
Star B
2
Star A
1
2
Celestial Sphere
Celestial Sphere
3
1
4
A.
B.
C.
D.
toward the South
toward the North
toward the East
toward the West
3
4
Celestial Sphere
Rotation
Figure 2
Horizon
Imagine that from your current location you
observe a star rising directly in the east.
When this star reaches its highest position
above the horizon, where will it be?
A.
B.
C.
D.
high in the northern sky
high in the southern sky
high in the western sky
directly overhead
Is there a location from which an
observer would see a star rise due
east, move directly overhead, and
then set due west?
A.
B.
C.
D.
E.
No, that never happens.
Only if the observer is located in the southern
hemisphere.
Only if the observer is located in the northern
hemisphere.
Only if the observer is located at the north pole.
Only if the observer is located at the equator.
In what direction would an observer
located at the north pole have to look
to see the north star?
A.
B.
C.
D.
E.
Along the northern horizon.
Along the southern horizon.
Directly overhead.
About 30 degrees above the northern horizon.
The north star cannot be seen from the north
pole.
In what direction would an observer
located at the equator have to look to
see the north star?
A.
B.
C.
D.
E.
Along the northern horizon.
Along the southern horizon.
Directly overhead.
About 30 degrees above the northern horizon.
The north star cannot be seen from the north
pole.
Where would
the observer
look to see the
star indicated by
the arrow?
Celestial Sphere Rotation
Star B
2
Star A
1
2
Celestial Sphere
Celestial Sphere
3
1
4
3
A.
B.
C.
D.
high in the Northeast
high in the Southeast
high in the Northwest
high in the Southwest
4
Celestial Sphere
Rotation
Figure 2
Horizon
How long did it
take to get this
picture?
Take out a piece
of paper and put
your name on it
along with your
answer!!
Earth’s
rotation
causes the
Sun, Planets,
Moon and
stars to
appear to
move when
viewed from
Earth
Day-to-Day Changes
• Solar day - period from one sunrise to the
next (24 hours)
• Diurnal motion - apparent daily progress of
the Sun and other stars across the sky due to
Earth’s rotation.
• Sidereal day - a day measured by the stars.
Due to Earth’s orbit around the Sun, this is
3.9 minutes shorter than a solar day.
Tutorial: Motion (p. 3)
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with
one another.
• Come to a consensus answer you both agree
on.
• If you get stuck or are not sure of your
answer, ask another group.
• If you get really stuck or don’t understand
what the Lecture Tutorial is asking, ask for
help.
Seasonal Changes
• Since Earth revolves (orbits) around the sun,
the darkened part of the earth faces a slightly
different direction each night. This is why we
see difference constellations at different times
of the year.
• Ecliptic - the path traced out by the sun on the
celestial sphere. The constellations the sun
passes through on the ecliptic are collectively
known as the zodiac.
Why do we experience
summer and winter?
A. The earth is at different distances from
the sun.
B. The sun experiences seasonal
variations in intensity.
C. The tilt of the earth affects how much
direct light we get, which results in the
summer and winter seasons.
Seasons and Tilt
Seasonal Changes
• Summer solstice - when the sun is at its
northernmost point above the celestial equator. This
is the northern hemisphere’s longest day of the year.
• Winter solstice - when the sun is at its southernmost
point below the celestial equator. This is the northern
hemisphere’s shortest day of the year.
• Equinoxes - two points where the ecliptic intersects
the celestial equator. The day and night are of equal
length at these two points.
• Autumnal equinox - on September 21.
• Vernal equinox - on or near March 21.
• One tropical year - the interval of time from one
vernal equinox to the next (365.242 days).
Long-Term Changes
• Sidereal year - time required for Earth to
make one orbit around the sun relative
to the stars (365.256 days).
• Precession - Earth’s axis changes
direction over time (like a spinning top).
Precession
Your Astrological Sign
ROUGHLY, it is the constellation that the
Sun is covering up during the day you are
born if you were born 2000 years ago.
Zodiac The 13 Zodiacal constellations that
our Sun covers-up (blocks) in the
course of one year
(used to be only 12)
•
•
•
•
•
•
Aquarius
Pisces
Aries
Taurus
Gemini
Cancer
•
•
•
•
•
•
•
Leo
Libra
Virgo
Scorpius
Ophiuchus
Sagittarius
Capricornus
The changing phases of the Moon originally
inspired the concept of the month
Lunar Phases
• Moon’s appearance undergoes a
regular cycle of changes or phases.
• New moon, waxing crescent, first
quarter, waxing gibbous, full moon,
waning gibbous, third quarter, waning
crescent, and back to new moon.
How long does it take to
complete the full cycle of
moon phases?
A. About a day
B. About a week
C. About a month
D. About a year
E. None of the above
Lunar Cycle
• Sidereal month - the time it takes the
moon to complete one revolution
around the earth (27.3 days).
• Synodic month - the time it takes the
moon to complete one full cycle of
phases (29.5 days).
Tutorial: The Cause of Moon
Phases (p. 79)
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with one
another.
• Come to a consensus answer you both agree on.
• If you get stuck or are not sure of your answer, ask
another group.
• If you get really stuck or don’t understand what the
Lecture Tutorial is asking, ask for help.
During any given phase, how
much of the moon’s surface is
illuminated by the sun?
A.
B.
C.
D.
All of the surface.
None of the surface.
Half of the surface.
Depends on what phase.
Eclipses
• An eclipse occurs during full or new moon when the
sun, earth, and moon all line up just right.
• Partial eclipse - what happens when the alignment is
off just a bit.
• Total eclipse - happens only when the alignment is
perfect.
• When the sun and moon are in opposite directions as
viewed from Earth, we get a lunar eclipse.
• When the sun and moon are in the same direction as
viewed from Earth, we get a solar eclipse.
Lunar Eclipse
Solar Eclipse
•
•
•
An eclipse occurs
during full or new
moon when the sun,
earth, and moon all
line up just right.
Partial eclipse - what
happens when the
alignment is off just a
bit.
Total eclipse - happens
only when the
alignment is perfect.
To get a solar eclipse, where
do the sun and moon need to
be located in the sky?
A. In opposite directions.
B. In the same direction.
C. None of the above.
Parallax
• Triangulation - foundation
of the cosmic distance
scale.
• Parallax - apparent
displacement of a
foreground object relative
to the background as the
observer’s location
changes.
Tutorial: Parallax and
Distance (p. 39)
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with one
another.
• Come to a consensus answer you both agree on.
• If you get stuck or are not sure of your answer, ask
another group.
• If you get really stuck or don’t understand what the
Lecture Tutorial is asking, ask for help.
The Scientific Method
• Theory - the framework of ideas and
assumptions used to explain some set
of observations and make predictions
about the real world.
• Scientific method - process of theory,
prediction, and observation.
Scientific Theories
• Must be testable.
• Must be continually tested.
• Should be simple. (Occam’s razor: If two competing
theories both explain the facts and make the same
predictions, the simpler one is better.)
• Should (in some sense) be elegant. When a simple
principle naturally explains several phenomena
previously thought to be distinct, this is widely
regarded as a strong point in favor of the new theory.