Transcript AXIS always points to Polaris

Earth’s Rotation
The spinning of earth on its AXIS
·AXIS tilted 23.5°
rotation west to east
·Counterclockwise from NP
·15°/hour
·AXIS always points to Polaris
What are the APPARENT DAILY
MOTIONS of Celestial Objects?
·The apparent motion is caused by Earth’s rotation
west to east 15 ° / hour (counterclockwise)
·For example, the stars appear to move from east to
west. The paths are circular or parts of a circle
called an arc.
Celestial Sphere:
A huge imaginary sphere around
the Earth to which the stars appear to be
attached.
But in reality the
celestial sphere is
stationary and the earth
is rotating
counterclockwise
ALL MOTION
15°/HR
Stars appear to be moving from east
to west. Stars rising in the east.
Stars appear to be moving from east to west.
Rise in the east and set in the west.
Stars appear to move in the shape of an arc east to west because
Earth is moving west to east (counterclockwise) except in the
Northern Sky where they circle Polaris
http://www.reviewearthscience.com/subjects/es/review/100ill/3.html
The complete circular path can be seen
for stars in the northern part of the sky
around Polaris
Circumpolar
constellations never set.
Circumpolar
constellations change
with latitude
STARS APPEAR TO ROTATE AROUND
POLARIS
The complete circular path can be seen
for stars in the northern part of the sky
around POLARIS
Circumpolar
Constellations
never set but
They do change
with latitude
LAB 1C: The Altitude of Polaris
Altitude of a Celestial Body – a
star’s angle above the horizon.
Polaris – the North Star
Horizon – the boundary between the
Earth’s surface and the sky.
How to find Polaris in the night sky
How does the SHAPE of the Earth
affect our view of the stars?
We will be taking a “virtual” field trip to
different spots on the Earth and viewing
the stars there.
We are going to focus in on two major
constellations, and one very important
star—Polaris, or the North Star.
As you may already know, our view of the
constellations change over an evening—the
stars appear to move because the Earth is
rotating!
Your view of the sky at 9:00 p.m. is different
from your view at 11:00 p.m.
We will be viewing the sky at the same time
in every location we go to!
****Polaris is the exception to this!!!
Here We Go!
Hop on board!
Hop on board!
Hop on board!
Hop on board!
Our first stop is
Central Park in New York City!
#1. New York, New York 41o N Latitude
Big Dipper
Cassiopeia
Polaris
Pointer Stars
We are going to “calibrate” our screen so that we can
make measurements of the location of Polaris in other
places on Earth.
We will be using a device called a “sextant.” This
measures the star’s angle above the horizon. This is
called ALTITUDE.
This simulation is only in 2-D, so the sextant appears
like a ruler. However, in the real-world of 3-D, this
device would measure what angle you have to tilt your
head up in order to see a star.
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New York, New York 41o N
60
Big Dipper
Cassiopeia
50
Polaris
40
30
Pointer Stars
Measure the altitude of
Polaris
20
10
0
What does this view “feel like” in 3-dimensions?
POLARIS
The arc represents the
Celestial hemisphere
(the sky above)
E
41o
HORIZON
N
S
The ground
W
There is a 41 degree angle between the horizon and Polaris.
In other words, the viewer must tilt his or her head (and telescope!) up 41o from the horizontal in order to
directly see Polaris.
What is the
latitude of NY
city?
BEFORE YOU MOVE ON TO
LOCATION #2, did you:
• Mark location #1 on the map (pg.3) with
a red or orange colored pencil.
• Plot Polaris on Dome #1 (pg.4) and fill in
the Location & Latitude.
Now let’s head to Tampa, Florida and
view the night sky there!
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#2. Tampa, Florida
What is the altitude
of Polaris in
Tampa?
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50
40
30
20
10
0
What is the altitude of Polaris in Tampa?
Again, let’s get a feeling of what this looks like in 3-D!
What does this view “feel like” in 3-dimensions?
Plot the position of
Polaris for Tampa
The arc represents the
Celestial hemisphere
(the sky above)
E
HORIZON
N
S
W
The ground
In Tampa, would you tilt your head up more or less
than in New York in order to see Polaris?
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Did you notice that
the Big Dipper, and
Cassiopeia are also
lower in the sky
here…
#2. Tampa, Florida
60
50
40
30
20
10
0
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#1. New York, New York 41o N
…than in
New York!
60
50
40
30
20
10
0
What is the
latitude of
Tampa?
SO WHAT HAVE WE
LEARNED ABOUT THE
ALTITUDE OF POLARIS
and LATITUDE?
Now we are flying off to
Popayán, Colombia in order to
view the tropical night sky!
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#3. Popayán, Colombia
What is the altitude
of Polaris in
Popayán?
60
50
40
30
20
10
0
What is the altitude of Polaris in Popayán ?
MARK IT ON DOME #3
What is the latitude of Popayán?
Plot it in Red on your map
Let’s see if you are getting the hang of
this! For our next stop we are going to
view the sky and then predict our
latitude from the altitude of Polaris!
#4. Mystery Location
O.K.!
Let’s determine the
altitude of Polaris…
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60
50
40
30
20
10
0
So where is Polaris in this location?
The arc represents the
Celestial hemisphere
(the sky above)
E
HORIZON
N
S
W
The ground
PLOT the Altitude of Polaris on your dome diagram
Of the
choices
given,
where in
the world
are we?
Churchill, Canada
Quebec, Canada
Hartford, CT
Washington, D.C.
New Orleans, LA
Now that you’re so good at this,
predict the altitude of Polaris at the
North Pole!
Let’s imagine what it would be like
to do this at the North Pole.
This is LOCATION #5
Be careful you don’t strain your
neck!
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40
30
20
10
80
70
60
50
40
30
20
90
80
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60
50
40
90
80
70
60
What is the altitude
of Polaris?
90
80
70
60
Where would Polaris be on your dome if you were
standing at the North Pole? PLOT IT
The arc represents the
Celestial hemisphere
(the sky above)
E
HORIZON
N
S
W
The ground
All aboard for our last stop! (Location #6)
Another mystery location for you to solve!
Mystery Location #6
60
50
40
30
20
10
0
Do the
measurement…
Of the
choices
given,
where in
the world
are we?
Churchill, Canada
Ottawa, Canada
Philadelphia, PA
Meridian, MS
Havana,
Cuba
Well, our adventuring is over for today! Thanks for
making our mission a success!
Well, our adventuring is over for today! Thanks for
making our mission a success!
Well, our adventuring is over for today! Thanks for
making our mission a success!
Well, our adventuring is over for today! Thanks for
making our mission a success!
Well, our adventuring is over! Thanks for making our
mission a success!
SUMMARY – Read & watch the remaining
slides to help answer the discussion questions.
Polaris – North Star
• If you can spot Polaris in the sky, you can
always tell which way is north. Because of
this, Polaris was the most important star for
navigating at sea.
- Polaris is a fixed point above the North Pole
- Polaris Changes in Altitude to an observer on
the Earth.
90º
Why do observations of Polaris help
determine the Earth’s shape?
Watch the animation on the next
slide to better understand.
Polaris – Fixed Point above the
North Pole
• Because of this, in the Northern Hemisphere, the altitude
(angle measured in degrees above the horizon) of Polaris
tells observer his latitude.
• If observer’s latitude changes in the Northern Hemisphere,
the altitude of Polaris will exactly match observer’s latitude.
ALTITUDE OF POLARIS = LATITUDE OF OBSERVER
Locating Polaris – our latitude is
41°N , Polaris’ altitude will be 41°