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Earth in Space

Earth in Space. Chapter 1 Section 1. Focus Questions. What causes day and night? What causes the cycle of seasons on Earth?. Days and Years. The ancient Egyptians were among the first people to study the stars Ancient astronomers also studies the movements of the sun and the moon

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Earth in Space

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  1. Earth in Space Chapter 1 Section 1

  2. Focus Questions • What causes day and night? • What causes the cycle of seasons on Earth?

  3. Days and Years • The ancient Egyptians were among the first people to study the stars • Ancient astronomers also studies the movements of the sun and the moon • It seems as though Earth was standing still • Sun and moon seem to move only because Earth is rotating • Astronomy – the study of the moon, stars and other objects in space

  4. Days and Years • Rotation – Earth’s spinning on it’s axis • 1,600 kilometers per hour • Earth’s axis is an imaginary line that passes through Earth’s center and the North and South poles • The north end of the axis points toward a point in space near Polaris (the North Star)

  5. Days and Years • Earth’s rotation on its axis causes day and night! • As Earth rotates eastward, the sun appears to move westward across the sky. • It is day on the side of the Earth facing the sun. (night on the side the sun cannot reach) • It takes 24 hours to rotate once on its axis.

  6. Days and Years • Revolution – the movement of one object around another object • Earth revolves around the sun. • One complete revolution around the sun is a year. • Earth’s path as it revolves around the sun is called its orbit. (flattened circle, or oval shape)

  7. Days and Years • Egyptian astronomers counted the number of days between each appearance between each first appearance of the star Sirius. • 365 days • Earth’s orbit around the sun is actually 365 ¼ days • Leap year – accommodate extra ¼ by adding an extra day every 4 years

  8. Seasons on Earth • Earth has seasons because its axis is tilted as it moves around the sun. • Warmer near the equator than at the poles because sunlight is hitting the surface more directly.

  9. Seasons on Earth • Tilt is 23.5◦ • Tilted toward the sun – summer • Tilted away from the sun – winter • Distance to the sun is not a factor

  10. Days and Years • Earth in June • The north end of Earth’s axis is tilted toward the sun • The noon sun is directly overhead at 23.5◦ north latitude (equator is 0◦) • Latitude – measurement of distance from the equator, expressed in degrees north or south.

  11. Days and Years • The hemisphere tilted toward the sun has more daylight hours than the hemisphere tilted away from the sun • Direct rays and more hours of sunlight heats the surface more than at any other time of the year

  12. Days and Years • Earth in December • At around December 21, the noon sun is overhead at 23.5◦ south latitude • Both June 21 and December 21 • Two days a year, the noon sun is overhead at either 23.5◦ north or south • Solstice!

  13. Days and Years • Earth in March and September • Halfway between the solstices, neither hemisphere it tilted toward the sun • The noon sun is directly overhead at the equator • Equinox! • Vernal equinox, or spring equinox, occurs around March 21 (beginning of Spring in NH) • Autumnal equinox, or autumn equinox, occurs around September 21 (beginning of Fall in NH)

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