For thousands of years, humans have used the stars to learn about
the planet we live on. From star sightings, you can map the change
of seasons, navigate the oceans, and even determine the size of
Earth.
Polaris, or the North Star, has occupied an important place in
human history. The location of Polaris is not affected by Earth's
rotation. At any given observation point, it always appears at the
same angle above the horizon. At Earth's North Pole, Polaris appears
directly overhead. At the equator, it is just above the northern
horizon. Polaris provides a standard from which other locations
can be measured. Such star sightings can be made using the astrolabe,
an instrument used to measure the height of a star above the horizon.
How can you determine the size of Earth? Knowing that Earth is round,
do you think you can estimate the circumference of Earth based on
star sightings.
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