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# CELESTIAL MOTIONS

## CELESTIAL MOTIONS

PURPOSE: Observing the daily and annual motions of the Sun, moon, stars and planets can be very confusing. For students of astronomy, one of the difficult tasks is to distinguish between that which is “real” and that which is “illusory”. For example, the daily westward motion of the sun was explained by the ancients by the Sun orbiting the Earth. To them, the observed motion was absolute. Today, of course, we know that the observed motion is apparent and is produced by the Earth’s rotation on its axis.

This laboratory exercise deals with two absolute motions of the Earth, rotation and revolution, and the observed effects they produce.

PREPARATION: The Good Earth Pages 42-4

PROCEDURE: Work through the exercises on the following pages and record your answers. Use complete sentences in your explanations. When recording measurements, be sure to record the appropriate units of measurements.

Submit the following lab exercise questions.  All explanations should be in complete sentences. All measurements should include the appropriate units of measurements.

The horizon is defined as the boundary where the sky seems to meet Earth’s surface.

The horizon is used for references in observations. Keeping this in mind, the imaginary line fort he horizon is marked off in degrees that can be used to locate objects.

1. How many degrees would an observer have to turn to encompass all directions on the horizon?
2.  On the horizon in Astronomy, the direction of North is always designated as 0 degrees. Imagine that as an observer, you are facing North.  If you turned eastward, what would be the angle in degrees designated for that 1/4 turn?  What angle in degrees equates to a 1/2 turn southward?  What angle in degrees would a westward turn be equal to?

The following questions focus on the Sun and the Earth:

The Sun appears to move across the sky during the course of a day

• In what compass direction does the sky appear to rise in the sky?
• 4. In what compass direction does the Sun appear to set in the sky?
•  Consider the fact that the motion of the Sun is an apparent motion and is produced by the Earth’s rotation on its axis.  In which direction must the Earth be rotating to produce the effects that are observed?
• What is the period of Earth’s rotation in hours?
• How many degrees would one rotation of Earth be equal to?
• Now use your above answers in Questions #6 and # 7 to calculate how many degrees the Earth rotates each hour.

Show your work and remember to include units of measurement.

• Does the planet Saturn rotate the same amount of degrees as planet Earth?

In this next section, the planets will be the main focus.

1. Is the motion of the planets across the sky considered to be absolute or apparent motion? Give 1 explanation to support your answer!
2. Which planet has the fastest orbital velocity around the Sun? Provide a detailed explanation for your answer.
3. Which planet has the slowest orbital velocity around the Sun?  Explain your answer providing details.
4. Is the planet’s motion around the Sun apparent or absolute? Explain your answer. These last 3 Questions are about the stars. A constellation is a group of stars forming a recognizable pattern that is traditionally named after its apparent form or identified with a mythological figure.
5. Name 3 well known constellations.
6. Why are different constellations visible in the night sky throughout the course of a year?  Be detailed in your explanation!!

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