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

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!

Our first stop is Central Park in New York City!

#1. New York, New York 41 o 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. ALTITUDE 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.

New York, New York 41 o N Big Dipper Cassiopeia Polaris Pointer Stars Measure the altitude of Polaris

N S W E 41 o POLARIS HORIZON 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 41 o from the horizontal in order to directly see Polaris. What does this view “feel like” in 3-dimensions? The arc represents the Celestial hemisphere (the sky above) The ground

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!

#2. Tampa, Florida What is the altitude of Polaris in Tampa?

What is the altitude of Polaris in Tampa? Again, let’s get a feeling of what this looks like in 3-D!

N S W E HORIZON What does this view “feel like” in 3-dimensions? The arc represents the Celestial hemisphere (the sky above) The ground In Tampa, would you tilt your head up more or less than in New York in order to see Polaris? Plot the position of Polaris for Tampa

#2. Tampa, Florida Did you notice that the Big Dipper, and Cassiopeia are also lower in the sky here…

#1. New York, New York 41 o N …than in New York!

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!

#3. Popayán, Colombia What is the altitude of Polaris in Popayán?

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…

N S W E HORIZON So where is Polaris in this location? The arc represents the Celestial hemisphere (the sky above) The ground PLOT the Altitude of Polaris on your dome diagram

Of the choices given, where in the world are we? New Orleans, LA Washington, D.C. Hartford, CT Quebec, Canada Churchill, Canada

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!

What is the altitude of Polaris?

N S W E HORIZON 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) The ground

All aboard for our last stop! (Location #6) Another mystery location for you to solve!

Do the measurement… Mystery Location #6

Of the choices given, where in the world are we? Meridian, MS Havana, Cuba Philadelphia, PA Ottawa, Canada Churchill, Canada

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°