Lecture02 - Lecture #2: The Sky and Historical Astronomy...

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1 Astro 102/104 1 Lecture #2: The Sky and Historical Astronomy • General Introduction to the Sky. • Coordinates: Getting your bearings. • Earth's spin and orbital motion. • Classical astronomy. • Modern astronomy. Astro 102/104 2 The Main Point The movements of the Sun, Moon, planets, and stars that we observe every day and night are apparent , not actual motions, because we are moving as well! Astro 102/104 3 General Introduction to the Sky • Watching and knowing the sky is the key to understanding our place in the Cosmos. • For most of human history, knowing the sky was critical for survival. • Today, hardly anyone ever looks up. .. • The sky moves! (or does it. ..) • Actual vs. Apparent motion. Astro 102/104 4 Coordinates: Getting your bearings
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2 Astro 102/104 5 Key concepts: •Zenith. • Horizon. • Celestial Sphere. • Celestial Pole. • Rotation Axis. • Celestial Equator. • Latitude. Astro 102/104 6 People living in different places on the Earth see different motions of the night sky. .. Astro 102/104 7 Earth's Spin and Orbital Motion • Earth spins once per day on its axis. – Not obvious! The sky appears to spin, not us ! • Earth orbits around the Sun once per year. – Not obvious! The Sun appears to orbit us ! • Earth's orbital plane is called the ecliptic – this is also the apparent path of the sun on the sky. • Earth's axis is tilted relative to its orbit: – The tilt angle ( obliquity ) is about 23.5°. – The tilt is the reason for the seasons! (Lec. 4). Astro 102/104 8 Key Concepts: • Earth's axis is tilted with respect to its orbital plane (ecliptic). • Tilt angle changes the angle of sunlight striking the Earth's surface. • At a fixed location on the
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This note was uploaded on 03/04/2008 for the course ASTRO 1102 taught by Professor Squyres,s/margot,j during the Spring '07 term at Cornell University (Engineering School).

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Lecture02 - Lecture #2: The Sky and Historical Astronomy...

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