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Exploring the Heavens
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Humans have always looked up at the sky and wondered
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Figure E.1 Size and Scale in the Universe
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The view from Earth Constellations The celestial sphere
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Figure E.2 Constellation Orion viewed from Earth
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Figure E.3 The Constellation Orion Distribution of Stars in Space
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Figure E.4 The Celestial Sphere
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Earth’s Rotation Spin of earth around its own axis Determines length of day Earth rotates toward the east
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Figure E.5 - The Northern Sky
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Celestial Coordinates Declination –Similar to latitude on earth Right Ascension –Similar to longitude on earth –Measured in hours/minutes/seconds
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Figure E.6 Right Ascension and Declination
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Earth’s Revolution Movement of earth around the sun Determines length of year Path is almost a circle (actually an ellipse)
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Length of a Day Sidereal Day - 23 h 56 m Earth rotates once relative to stars Solar Day - 24 h Earth rotates once relative to sun About 4 minutes longer than sidereal day
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Figure E.7 Solar and Sidereal Days
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Figure E.8 - The Zodiac
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Figure E.9 - Ecliptic
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Length of a Year Tropical year - 365.242 solar days Time from one vernal equinox to the next Calendars based on it Sidereal year - 365.256 solar days Revolution around sun, relative to stars
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Figure E.10 - Seasons
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Figure E.11 Earth’s Orbit
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Figure E.12 Precession
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The Moon’s orbit Lunar phases Lunar Eclipses Solar Eclipses
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Figure E.13 Lunar Phases
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Lunar Month Sidereal Month - 27.3 days One revolution on the celestial sphere Synodic Month - 29.5 days Full cycle of phases
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Figure E.14 - Lunar Eclipse
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Figure E.15 - Solar Eclipse
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Figure E.16 - Solar Eclipse Types
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Figure E.17 - Eclipse Geometry Moon’s orbit tilted 5° to the ecliptic
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Figure E.18 - Solar Eclipse Tracks
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Measuring Distance Angular Measure Triangulation Parallax
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More Precisely E-1 - Angular Measure Degrees, minutes and seconds of arc
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Figure E.19 - Triangulation
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Figure E.20 Parallax
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Figure E.21 Parallax Geometry
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More Precisely E-2a Measuring Distances with Geometry
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More Precisely E-2b Measuring Distances with Geometry
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Figure E.22 - The Scientific Method
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Scientific Theories Must be testable Must be continually tested Should be simple Should be elegant Theory has a different meaning in science as opposed to general usage
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Figure E.23 - The Scientific Method Aristotle and lunar eclipses
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Measuring Size of Earth Eratosthenes –276 - 194 B.C. Alexandria and Syene (Aswan) Measured radius with 1% accuracy
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Discovery E-1 Sizing up Planet Earth
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