exploring the heavens. humans have always looked up at the sky and wondered

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