= 1 meter) between the clipboard and the index card. Before you can correctly solve this
equation, you will need to change all of your measurements to the same unit - in this case,
change all your measurements to km. Try this out and see how accurately you can measure
the true diameter of the Sun.
24.5 The Sun and the Earth-Moon System
Lesson Objectives
- Describe how Earth’s movements affect seasons and cause day and night.
- Explain solar and lunar eclipses.
- Describe the phases of the Moon and explain why they occur.
- Explain how movements of the Earth and Moon affect Earth’s tides.
Introduction
The solar system is made up of the Sun, the planets that orbit the Sun, their satellites,
dwarf planets and many, many small objects, like asteroids and comets. All of these objects
move and we can see these movements. We notice the Sun rises in the eastern sky in the
morning and sets in the western sky in the evening. We observe different stars in the sky
at different times of the year. When ancient people made these observations, they imagined
that the sky was actually moving while the Earth stood still. In 1543, Nicolaus Copernicus
(Figure24.21) proposed a radically different idea: the Earth and the other planets make
regular revolutions around the Sun. He also suggested that the Earth rotates once a day on
its axis. Copernicus’ idea slowly gained acceptance and today we base our view of motions in
the solar system on his work. We also now know that everything in the universe is moving.
In this lesson you will learn about how the movements of the Earth, Moon, and Sun affect
different phenomena on Earth, including day and night, the seasons, tides, and phases of the
Moon.
Positions and Movements
Earlier we discussed Earth’s rotation and revolution. The Earth rotates once on its axis
about every 24 hours. If you were to look at Earth from the North Pole, it would be
spinning counterclockwise. As the Earth rotates, observers on Earth see the Sun moving
across the sky from east to west with the beginning of each new day. We often say that
the Sun is “rising” or “setting,” but actually it is the Earth’s rotation that gives us the
perception of the Sun rising up or setting over the horizon. When we look at the Moon or
the stars at night, they also seem to rise in the east and set in the west. Earth’s rotation is