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7.1 Ancient Astronomy. What do you call a tick that lives on the moon?. A lunatic!!. Vocab Words. celestial object astronomer revolution rotation. Human survival depends on the reliability of the Sun rising every morning and the seasons returning every year.
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Vocab Words • celestial object • astronomer • revolution • rotation
Human survival depends on the reliability of the Sun rising every morning and the seasons returning every year. • During a solar eclipse, the moon passes in front of the sun and temporarily blocks the Sun’s light.
Early Calendars and Sky Observations. • A calendar is a way of showing days. The days are organized into a schedule of larger units of time, such as weeks, months, seasons, or years. • Calendars allow people to predict other important events, such as spring rains, the annual flooding of rivers and lakes, and the migration of birds, insects, and herds of animals.
Fishers and travellers knew the fixed patterns of the stars in the sky and used them to help them find their way, or navigate, on land and water. • The ancient Egyptians relied on a star called Sirius to let them know when the Nile river was about to flood. Sirius rises just before dawn at the same time every year before the annual flooding.
Early Astronomers • Early ancestors paid close attention to the sky and tried not to offend the Gods who they believed ruled the skies. • A sign such as an eclipse they believed meant that the deities were getting restless and they would do something they thought would please them to return order to the sky.
From this grew the role of celestial priests and priestesses who studied celestial objects such as the Sun and other stars, the Moon, and the planets to predict celestial events such as seasons and eclipses.
Mesopotamian Astronomers • The Mesopotamians were the first astronomers that we have evidence of their observations. Their calendars were thorough and having a calendar meant that organized agriculture was possible. • Producing extra food meant that other people in these societies could be freed up from farming to focus o skills such as wood working and metallurgy.
Today’s Year • Our year is determined by the amount of time it takes for Earth to make one revolution around the Sun. • This means that a year is 365.24 days long.
One day is the average time it takes for Earth to make one rotation on its axis with respect to the Sun. The first clocks were simply pillars and sticks in the ground and people would use the shadows they cast to tell the time of day.
Inferring Earth’s Spherical Shape • The ancient Egyptians thought that Earth was flat and supported by mountains at four different places. Originally the Greeks thought that Earth floated in the ocean like a piece of wood floats in water. • Eratosthenes and Aristarchus hypothesized the Earth is spherical and that the apparent flatness of Earth is an illusion created by Earth’s enormous size and they had 3 pieces of evidence to back it up:
1. Disappearing Ships • As a ship sailed out into the Mediterranean Sea, the hull disappeared below the horizon but the masts and sails were still visible. Eventually all of the ship would disappear as the ship moved farther away.
2. The Changing Sky • When travelling farther north they saw that stars were rising farther above the northern horizon and when traveling south they saw stars they had never seen before at all.
3. Earth’s Curved Shadow • When studying an eclipse of the Moon they noticed that the shape of Earth’s shadow was always curved. • Using this knowledge Aristarchus calculated the relative size of the Sun and Moon as well as the relative size of the Earth and the distance from Earth to the Sun.
Eratosthenes knew that on the summer solstice at local noon in Syene on the Tropic of Cancer, the sun would appear at the zenith, directly overhead He also knew, from measurement, that in his hometown of Alexandria, the angle of elevation of the sun was 1/50th of a circle (7°12') south of the zenith on the solstice noon. Assuming that the Earth was spherical (360°), and that Alexandria was due north of Syene, he concluded that the meridian arc distance from Alexandria to Syene must therefore be 1/50 = 7°12'/360°, and was therefore 1/50 of the total circumference of the Earth. • Calculating the circumference • of the Earth
Review questions: • P.276# 1,2,5,8
