Astronomy 101Astronomy 101Section 020Section 020

Lecture 3Lecture 3

A Dynamic Example: Motions of the Earth and A Dynamic Example: Motions of the Earth and MoonMoon

John T. McGraw, ProfessorJohn T. McGraw, Professor

Laurel Ladwig, Planetarium Laurel Ladwig, Planetarium ManagerManager

Day, Night and the Motion of the Day, Night and the Motion of the Stars - The Diurnal (Daily) MotionStars - The Diurnal (Daily) Motion

Half of the Earth (and Moon and every other planetary Half of the Earth (and Moon and every other planetary body) is always illuminated by the sun.body) is always illuminated by the sun.

Rotation causes the apparent Rotation causes the apparent diurnaldiurnal changes in the sky. changes in the sky.

Why the Why the Constellations Constellations Change During the Change During the YearYear

Revolution of the Revolution of the Earth about the sun Earth about the sun causes the causes the annualannual changes in the sky.changes in the sky.

The Reasons for SeasonsThe Reasons for Seasons

The Earth’s rotation axis is tilted 23.5° to the The Earth’s rotation axis is tilted 23.5° to the eclipticecliptic.. The The eclipticecliptic is the plane of the Earth’s orbit about the is the plane of the Earth’s orbit about the

sun.sun.

Solar Energy: Designing Your HouseSolar Energy: Designing Your House

The Ecliptic, Equinoxes and SolsticesThe Ecliptic, Equinoxes and Solstices

The The eclipticecliptic (green) is the plane of the Earth’s (green) is the plane of the Earth’s orbit around the sun.orbit around the sun.

That Winter/Summer Thing AgainThat Winter/Summer Thing Again

Some snappy circles!Some snappy circles!

Time Zones Aid the Human (Rat?) Time Zones Aid the Human (Rat?) Race!Race!

Time zones are the result of the Earth’s rotation.Time zones are the result of the Earth’s rotation. When it is noon in Des Moines, what time is it in LA? In When it is noon in Des Moines, what time is it in LA? In

Miami?Miami?

The Motions of the Moon: Lunar Phases and The Motions of the Moon: Lunar Phases and Synchronous RotationSynchronous Rotation

The moon’s phases The moon’s phases result from its result from its revolutionrevolution about the about the Earth.Earth.

Synchronous rotationSynchronous rotation means that one side means that one side of the moon always of the moon always faces the Earth. The faces the Earth. The moon rotates once moon rotates once per revolution.per revolution.

Orbit and Phases of the MoonOrbit and Phases of the Moon

Phases and Shadows: A DemonstrationPhases and Shadows: A Demonstration

The Moon’s Synchronous Rotation:The Moon’s Synchronous Rotation:A DemonstrationA Demonstration

The “Coming Together” and “Starry” The “Coming Together” and “Starry” Months:Months:

Synodic and Sidereal PeriodsSynodic and Sidereal Periods

The 5° Inclination of the Moon’s Orbit The 5° Inclination of the Moon’s Orbit Relative to the EclipticRelative to the Ecliptic

How How EclipsesEclipses Can Occur Can Occur

Three Types of Three Types of Lunar EclipsesLunar Eclipses

A Total Lunar EclipseA Total Lunar Eclipse

The Geometry of a The Geometry of a Total Solar EclipseTotal Solar Eclipse

Solar EclipsesSolar Eclipses

Total (1991, La Paz) and annular (1973, Total (1991, La Paz) and annular (1973, Costa Rica) solar eclipses.Costa Rica) solar eclipses.

Eclipse Paths for Total Solar Eclipses:Eclipse Paths for Total Solar Eclipses:1997 - 20201997 - 2020