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Planetarium Program
part III for
The Sun in Time

sun_in_time_ssm.jpg (10439 bytes)

{For our readers in the southern hemisphere, you will need to adjust this section for your part of the world.  You, of course, don't have a "South Star" but your planetarium will show circumpolar motion about the southern pole.  You would use that area of the sky as a starting point for the following discussion and point out, for example, Musca, Mensa, and Tucana as circumpolar constellations.}

Point out Polaris and Merak and Dubhe

Let's start here in the northern part of sky where we find Polaris, the North Star.  When I was young, I thought the North Star was important because it was big and bright---not so!  Polaris is a fairly ordinary star, except for one thing:  it doesn't appear to move in the sky. 

To find Polaris, we use the stars of the Big Dipper, found over here.  Take the two outer stars of the bowl (called Merak and Dubhe), and extend a line from Merak to Dubhe and beyond.  The first more-or-less bright star you come to, is the North Star, Polaris.

Turn on Celestial Meridian

Not only can the North Star show us where North is, it can also tell us where on Earth we are.  If I put up the Celestial Meridian, you can see that the Meridian rests on top of the North Star.  You can then read on the scale the height (in degrees) of the North Star above the horizon.  It's the same as our latitude! If we visit the North Pole, Polaris would be directly over our heads and would be at a height of 90° above the horizon...our latitude would be...90° (North).  If we were at the equator, Polaris would lie exactly on the northern horizon, it's altitude would be 0° and so would our latitude.  Easy, huh?

Many ancient peoples saw bears where we see dippers.  Now I don't know about you, but I don't see a bear where I do see a Big Dipper and I know why.  It's a problem called light pollution.  Our modern world is a wonderful place, filled with many things to do...including activities at night.  For instance, ball games, shopping at the mall, visiting people...all these things are possible or made easier to do at night because we have electric lights.  But much of this light is aimed at the sky. In much the same way as the sun affects the sky during the day, the light from the stars at night is washed out, causing the stars to be hidden from our view.  However, if we could get away from city lights, to a really dark nighttime sky, the view would be something like this...

Fade house and/or cove lights completely down. Point out Ursa Major.

Now, let's find a bear!

Before electric lights, the sky would have looked a lot like this.  Over the entire globe, people tried to create order from chaos and saw patterns in the stars.  Once they saw patterns, they told stories about these stellar dot-to-dot pictures which we call constellations.  In England the Big Dipper is called the Plow.  In Egypt it was the foreleg of a bull.  A little over a hundred years ago, escaping slaves fleeing North were told to follow the "Drinking Gourd." 

Turn on positive daily motion

Point out Cepheus and Cassiopeia and Ursa Major as circumpolar constellations...not necessarily identifying them by name.  Now stop daily motion.

Now if I turn on the sky motion, and let some time go by, you see stars rise in the East and set in the West...but the North Star appears to stand still.  You'll also see that some constellations close to Polaris, seem to move in a circle around the Pole Star.  These constellations never set at our latitude (approximately 34° and higher); these are called circumpolar constellations.

You can simulate this motion in your classroom like this: stand next to your desk, look at the ceiling and find a spot or dot above your head.  Point at this spot and continue to look at it as you turn around.  As you turn, you will see everything in your peripheral vision move, but your spot will appear to stand still.

To return to Part II of the Planetarium Program, click here.

To return to Part I of the Planetarium Program, click here.

To return to the Slide Show Index, click here.

To return to the Sun in Time home page, click here.