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Exploring the HeavensExploring the Heavens
Humans have always looked up at the sky and wondered
Figure E.1Size and Scale in the Universe
The view from EarthThe view from Earth
• Constellations
• The celestial sphere
Figure E.2Constellation Orion viewed from Earth
Figure E.3The Constellation Orion
Distribution of Stars in Space
Figure E.4The Celestial Sphere
Earth’s RotationEarth’s Rotation
• Spin of earth around its own axis
• Determines length of day
• Earth rotates toward the east
Figure E.5 - The Northern Sky
Celestial CoordinatesCelestial Coordinates
• Declination
– Similar to latitude on earth
• Right Ascension
– Similar to longitude on earth
– Measured in hours/minutes/seconds
Figure E.6Right Ascension and Declination
Earth’s RevolutionEarth’s Revolution
• Movement of earth around the sun
• Determines length of year
• Path is almost a circle (actually an ellipse)
Length of a DayLength 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
Figure E.7Solar and Sidereal Days
Figure E.8 - The Zodiac
Figure E.9 - Ecliptic
Length of a YearLength 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
Figure E.10 - Seasons
Figure E.11Earth’s Orbit
Figure E.12Precession
The Moon’s orbitThe Moon’s orbit
• Lunar phases
• Lunar Eclipses
• Solar Eclipses
Figure E.13 Lunar Phases
Lunar MonthLunar Month
• Sidereal Month - 27.3 days
• One revolution on the celestial sphere
• Synodic Month - 29.5 days
• Full cycle of phases
Figure E.14 - Lunar Eclipse
Figure E.15 - Solar Eclipse
Figure E.16 - Solar Eclipse Types
Figure E.17 - Eclipse GeometryMoon’s orbit tilted 5° to the ecliptic
Figure E.18 - Solar Eclipse Tracks
Measuring DistanceMeasuring Distance
• Angular Measure
• Triangulation
• Parallax
More Precisely E-1 - Angular Measure Degrees, minutes and seconds of arc
Figure E.19 - Triangulation
Figure E.20Parallax
Figure E.21Parallax Geometry
More Precisely E-2aMeasuring Distances with Geometry
More Precisely E-2bMeasuring Distances with Geometry
Figure E.22 - The Scientific Method
Scientific TheoriesScientific 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
Figure E.23 - The Scientific MethodAristotle and lunar eclipses
Measuring Size of EarthMeasuring Size of Earth
• Eratosthenes
– 276 - 194 B.C.
• Alexandria and Syene (Aswan)
• Measured radius with 1% accuracy
Discovery E-1Sizing up Planet Earth
