Astronomy 1010Fall_2015Day-10

Planetary Astronomy

Course Announcements• SW chapter -2 due: Mon. 9/21; 2pm• How is the lunar observing going?• 1st Quarter night – Mon. 9/21 -7:30pm – on campus• Exam 1: Mon. Sept. 21• This Week: APSU-OUR: Research & Creative Activity

Week. Events in the library 2:30-3:30 every day.

Stuff in Chapter 2• Coordinates• Position• Daily Motion (spin of Earth on its

axis)• Visibility of the sky• Year Motion (Earth orbits the Sun)• Seasons (tilt of the Earth’s axis)• Precession of the equinoxes• Motion and phases of the Moon• Eclipses

Precession

Currently, the north celestial pole is near the bright star Polaris.

Earth’s axis wobbles with a period of 26,000 years.

Location of the poles slowly shifts.

Earth wobbles like a top, slowly. Since the axis shifts, the equator shifts. Positions of the equinoxes precess as well.

Stuff in Chapter 2• Coordinates• Position• Daily Motion (spin of Earth on its

axis)• Visibility of the sky• Year Motion (Earth orbits the Sun)• Seasons (tilt of the Earth’s axis)• Precession of the equinoxes• Motion and phases of the Moon• Eclipses

The Moon’s Motions

Because the orbit is elliptical and not circular, the rotation speed doesn’t always match the orbital speed.

Full Moon to Full Moon takes 29.53 days

The moon takes the same amount of time to complete one rotation as it does to complete one orbit

Cycle of phases:The synodic month 29.53 days

The Orbital Period is the Sidereal Month: 27.32 days

Lecture – TutorialCause of Moon Phases: pg 81

Work with a partner!Read the instructions and questions carefully.Discuss the concepts and your answers with

one another.Come to a consensus answer you both agree on.If you get stuck or are not sure of your answer,

ask another group.If you get really stuck or don’t understand what

the Lecture Tutorial is asking, ask one of us for help.

i_Clicker QuestionClassAction: Questions: Lunar Cycles: Phase Evolution; option 1

Lecture – TutorialPredicting Moon Phases: pg 85

Work with a partner!Read the instructions and questions carefully.Discuss the concepts and your answers with

one another.Come to a consensus answer you both agree on.If you get stuck or are not sure of your answer,

ask another group.If you get really stuck or don’t understand what

the Lecture Tutorial is asking, ask one of us for help.