Wednesday, Sept. 10
& Friday, Sept. 12
A100
Solar System
 Read Chapter 1 in text – History of Astronomy
Rooftop, Kirkwood Sessions TONIGHT
 1st Homework due Friday (get it on Oncourse)
Today’s APOD
The Sun Today
Kirkwood and Rooftop Sessions
• Kirkwood Observatory
– Open 9:30-11:30 PM (about 30 minutes)
– West end of Dunn’s Woods, near 4th & Indiana
• Rooftop – Swain West
– 9 PM
– Elevator to 3rd floor, follow signs to roof
– Rain date Sept. 11
• PRINT WORKSHEETS FROM ONCOURSE
(SYLLABUS TOOL) BEFORE YOU COME
SPECIAL
Opportunities!
• SCOPEOUT in Cincinnati: Sept. 13
– www.cincinnatiobservatory.org/scopeout
– Phil Plaitt (Bad Astronomy)
• Astronomy Day – Stonebelt Stargazers
– Sept. 13
– Wal-Mart in Bedford, 4-8 PM
Jupiter & the Moon in Sagittarius
Just look south… Jupiter is the brightest
object in the southern sky
Sept 8
Sept 9
Finding
Polaris
North
Big Dipper’s on
its side in the
northwestern
sky
Find an open
area away
from nearby
lights where
you have a
good view of
the sky
Find the Big
Dipper in the
northwestern sky
South
Sky chart for 9 PM TONIGHT
Finding
Polaris
To find Polaris:
• find the Big Dipper
• follow to Polaris
• the Big Dipper is ALWAYS up
in Indiana!
The Celestial Sphere
The stars all appear
to lie on a large
sphere surrounding
the Earth (the
celestial sphere)
Really, the stars
are all at different
distances
The
Local
Sky
An object’s altitude (above horizon) and direction
(along horizon) gives its location in your local sky
Our view from Earth:
• Stars near the north celestial
pole are circumpolar and never
set.
• All other stars (and Sun, Moon,
planets) rise in east and set in
west.
A circumpolar
star never sets
Celestial equator
This star never
rises in Indiana
Altitude of the celestial pole
= your latitude
Why do the constellations we see
depend on latitude and time of year?
 They depend on latitude because your
position on Earth determines which
constellations remain below the
horizon.
 They depend on time of year because
Earth’s orbit changes the apparent
location of the Sun among the stars.
The sky changes as Earth orbits the Sun
As the Earth
orbits the Sun,
different
constellations are
visible at night
At midnight, the
stars on our
meridian are
opposite the Sun
in the sky
Vocabulary Review
o Constellation
o Ecliptic
o Equator
o Celestial sphere
o Latitude
o Longitude
o Meridian
o Zenith
o Horizon
o Altitude
o North and south
celestial poles
Visualizing
Space
Expert Methods for
Visualization
Draw diagrams
Use 3d models
Use visualization
software
If you have a chance, visit
a planetarium…
Visualize the
Earth from
Space
• Pretend you are
Superman!
• What do you see?
–
–
–
–
Earth
Moon
Sun
Stars
Copyright 1980 by DC Comics Inc.
Welcome
to
Outer
Space!
Which of the following four diagrams most accurately
depicts the Earth's orbit around the Sun?
The Solar System from Overhead
• space.jpl.nasa.gov
The Solar System
from “Overhead”
• Earth’s Orbit
– 91,369,000 miles on Jan 4 (minimum)
– 94,776,000 miles on July 4 (maximum)
– average distance is 92,918,000 miles
– Varies +/- about 2% from a perfect circle
Basic Ideas
• The Earth orbits the
Sun in one year
(revolves)
• The Earth spins
around once each day
(rotates)
• The Moon orbits the
Earth about once a
month (revolves)
Where are
Mars, Earth
the Moon
and the
Sun?
The Earth
and Moon
from Mars
Visualizing the
Earth in Space:
What causes
the Seasons…?
True or False?
The Earth has seasons
because…?
• The Earth moves closer to or farther
from the Sun - it’s closer in the summer
and farther in the winter.
December
Weather
IU’s Rose
Well House
Bondi Beach Sydney, Australia
When is the Earth
closest to the Sun?
A.
B.
C.
D.
Winter
Spring
Summer
Fall
Visualizing
Seasons –
What
really
happens?
• Textbook applet: cause_of_seasons.htm
Which of the following best
explains why it is hotter in Indiana
in June than it is in December?
A
The Sun gives off
more heat energy
in June.
B
The Northern Hemisphere
is closer to the Sun in June.
C
The Sun is higher in the sky
and and provides more hours
of daylight in June.
D
Earth is closer to
the Sun in June.
With thanks to Bill Watterson, 1990
Visualizing the Moon
How can we understand
the phases of the Moon
as it circles around the
Earth?
Galileo Galilei's "The Phases of the Moon"
Image courtesy of Biblioteca Nazionale
Florence, Italy
Sometimes the Moon
looks like this
And sometimes the
Moon looks like this
What causes the Moon to change its appearance in
this way?
A. As the Moon orbits Earth, Earth's shadow covers the
Moon.
B. Clouds block part of the Moon from our view so it is
full sometimes and covered other times.
C. As the Moon orbits Earth, the part of the Moon
facing Earth is facing away from the Sun.
The
Earth
and
Moon
from
Space
Thinking about the Moon
• How much of the Moon receives sunlight at a given
time? Always half the Moon? Sometimes more or less
than half? Why?
• During new moon (when the moon appears dark) is
sunlight falling anywhere on the Moon's surface? If
not, why not? If so, why don't we see it?
• Is the Earth or the Moon closer to the Sun at new
moon?
• Which is closer to the Sun at full moon?
The Moon moves in its orbit about
12 degrees per day
It rises about an hour later each
night. Why?
Bring the perspective back to Earth
Ansel Adams; copyright © 2000 George Eastman House, Rochester, NY
Understanding the Moon in the Sky
I’m really
way off to
the right
Now
I’m
right
here!
Moon and
Venus before
Dawn
Where are the
Earth, Moon and Sun
in 3-dimensional
space?
Where is Venus?
The
Libration
of the
Moon
One question I’ve always had
about astronomy is…
Dates
to
ASSIGNMENTS
Remember
this week
 Read Chapter 1, History of…
 Kirkwood Obs. TONIGHT
 Rooftop Sky Viewing TONIGHT
 1st HW due Friday