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
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.
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.