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## Web Assignment: How does the Sun Move?

### Introduction

You know that the Sun rises in the East and sets in the West. At least, you should know this (and now you do). But what path does it take in between? Does it go straight up to the highest point in the sky? Does it move in a straight line or along a curved path? What is it that changes from one season to another about how the Sun moves? What difference does the latitude of the observer make?

Your assignment is to answer these questions. Find out how the Sun moves in Winter, Spring, Summer and Fall at three different latitudes: 90° N (at the North Pole), 43° N (Scarborough’s latitude), and 35° S (Buenos Aires, Argentina). Use the Internet and The Sky astronomy software (or other planetarium software, if available) to view the motion of the Sun during each of the following special calendar days:

• Winter Solstice
• Spring Equinox (aka Vernal Equinox)
• Summer Solstice
• Fall Equinox (aka Autumnal Equinox)

As part of your work, carefully define each of these days in your own words. To define them fully you will need to draw a picture of the Earth in its orbit around the Sun. Downloaded pictures are not acceptable: your illustration must be hand drawn. Explain what these terms mean regarding the seasons in which they occur. Ever wondered what someone meant when they said “The first day of Summer”? Now you will find out.

Define the motion based on the following:

• The four cardinal directions: North, East, South, and West
• Altitude: how far from the horizon in angular degrees?
• The Zenith: the highest point in the sky at any moment, 90° from every point on the horizon
• The Meridian: the imaginary line that runs from the point on the horizon that is due South, through the Zenith, and ends at the point on the horizon that is due North.
• The Celestial Sphere: the coordinates in the sky that are based on Earthly latitude and longitude. The Earth’s equator, north pole, and south pole define the celestial equator, celestial north pole, and celestial south pole.

Be able to answer the following questions about each of the three given locations. Does the Sun rise exactly due East on every day of the year? When does it do so, if ever? Similarly, does it set exactly due West at any time during the year? How far North or South of due East does the Sun rise on each of the special days? Answer the same question for where the Sun sets toward the West. When does the Sun cross the Meridian each day? How far from the horizon is it at that time on each of the special days? All of these questions must be answered for each of the three locations.

Draw a pictures showing the motion of the Sun in the sky in each location for each of the special days. In your picture include the horizon, the celestial sphere, and label the cardinal directions. One picture for each location may be sufficient if you can fit the motion of the Sun on each of the four days, otherwise four different pictures may be required.

Finally, find out how the Sun moves through the sky against the background of stars. What constellation does the Sun appear in during each of the twelve months of the year? What direction does it move against the background? Hint, you will need to know and be able to define in your own words: Celestial Sphere, Zodiac, and ecliptic

We will spend about a week in the computer lab to work on this assignment. We will take one day of that week to discuss your progress and define terms. The idea is that you must wrestle with figuring things out on your own before a class discussion of it will make sense. Your final product will be an illustrated report. Better grades are given for good explanations, high-quality, original illustrations, and attractive presentations.

Last updated: Sep 13, 2007        Home