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Ch. 1 Charting the Heavens

Explore the vastness of the universe in this comprehensive guide. Learn about astronomy and the concept of light-years, which measure vast distances in space. Delve into the fascinating world of constellations—including the origins of the Big Dipper across various cultures. Understand Earth's orbital motion, its seasonal changes, and the significance of equinoxes and solstices. Discover ancient techniques for measuring Earth, including Eratosthenes' impressive calculations of the planet's circumference. Your journey through the cosmos begins here!

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Ch. 1 Charting the Heavens

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  1. Ch. 1 Charting the Heavens

  2. Our Place in Space - vocab • Universe: totality of all space, time, matter and energy • Astronomy: study of the universe • Light year: distance light travels in one year, equal to 300,000 km/sec (Earth’s diameter is 1/20th of a light-second)

  3. Constellations • We recognize 88 constellations • Most of the constellations we know are from the Greek/Roman era • However, many cultures had constellations, some using the same stars • The Big Dipper is: • The “plow” or “wagon” is Western Europe • The leg of an ox in Egyptian mythology • A stag in Siberia • A funeral procession in some Native American cultures

  4. The Celestial Sphere • The ancient Greeks believed that a transparent globe surrounded the Earth, to which the stars were attached. • This globe revolved around the Earth, making the constellations move. • Celestial poles: points where Earth’s axis intersects the celestial sphere

  5. Earth’s Orbital Motion • Solar day: 24 hrs • Sidereal day: a day measured by the stars, 23 hrs, 56 minutes long • Why the difference? • Earth moves in its orbit as it revolves around the sun • How many degrees does Earth rotate per hours? • 360 ̊ /24 hrs = 15 degrees

  6. Seasonal Changes • Summer solstice: (near June 21st) most sunlight hours, “longest day”, sun reaches highest point in the sky • Winter solstice: (near December 21st), least daylight hours, “shortest day”, sun reaches lowest point in the sky

  7. Seasonal Changes • Equinoxes: 2 days in which day and night are equal in length • Vernal equinox: (March 21st) • Autumnal equinox: (September 21st)

  8. Long-Term Changes • Precession: movement of the Earth that takes 26,000 years, changes the direction that the Earth’s axis points • Tropical year: 365.242 days (we use this one in our calendars) • Sidereal year: 365.256 days • Why the difference? • Earth’s precession

  9. Measuring Earth • 200 BC • Greek philosopher Eratosthenes will calculate the circumference of Earth • He used the noon day sun in two different cities to calculate the angle of the sun in the sky • The angles were separated by about 7.2 degrees…1/50th of a circle. • So…he multipled the distance between the two cities by 50. • He got 24, 428 miles • The actual circumference is 24, 908 miles

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