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