Astronomy 1010Fall_2015

Day-9Planetary 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.

Useful Information for Next LabMotions of the Sun

ClassAction Web Site (Link from apsu.edu/astronomy)

Print the instructions BEFORE you come to class!

That Picture Question

• 37: <= 12hrs• 14: 24 hrs• 5: 10 hrs• 4: 6 hrs• 3: 14-16 hrs• 2: “A night”• 2: Answer had nothing to do with question• 1: 5hr, 9.5hr, 8hr, 72 hrs,6 min, “Couple of days”, No

Answer

i_Clicker QuestionClassAction: Questions: Basic Motion: Seasonal Analogy

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

Earth’s Axis

Earth’s axis is not perpendicular to the ecliptic plane.

Instead, it is at an angle of 23.5 degrees. This is why there are seasons.

Earth’s Axis

The angle of sunlight is closer to perpendicular in summer.

Energy is more concentrated. The southern hemisphere is opposite the

northern hemisphere.

Special Days of the Year

Summer solstice: Sun farthest north.

Autumnal equinox: Sun on the equator, moving southward.

Winter solstice: Sun farthest south.

Vernal equinox: Sun on the equator, moving northward.

Lecture – TutorialPath of the Sun: pg 89

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

each other.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: Coords & Motion: Sun Path 1

i_Clicker QuestionClassAction: Questions: Coords & Motion: Sun Shadow

Lecture – TutorialSeasons: pg. 93

Work with a partner!Yada Yada Yada …This one is homework

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.