1. Precession
Eric Angat
Teacher

2. What is the orbital tilt of Earth?
Copy and answer the following questions.
What is precession?
What is the orbital tilt of Earth?
What are the two factors that causes the precession of Earth?
What is our current north star?

4. Imbalance on the distribution of lands.
flattening
Earth's daily rotation at about 1,000 mph. This produces flattening at the poles and bulging at the equator.
bulging
bulging
flattening

5. What is Precession? Remember: Earth’s axis is only an imaginary line.
nutation
Earth’s axis
rotation
Remember: Earth’s axis is only an imaginary line.
Earth

6. Comparing Rotation and Precession
Earth’s axis spins.
Earth spins.
Spinning
Day and night.
Changes our North star.
24 hours
26,000 years

7. What is Precession? Precession is the rotation of Earth’s axis.
nutation
Earth’s rotation takes 24 hrs. while Earth’s axis rotation takes
26,000 years.
Earth’s axis
rotation
Earth

8. What is the orbital tilt of Earth?
Earth’s orbital tilt is degrees. This tilt is responsible for the seasons on Earth.

9. 1. Earth’s shape is oblate spheroid.
What are the two factors that causes the precession of Earth?
1. Earth’s shape is oblate spheroid.
The spinning motion of Earth causes it to bulge at the equator.

10. 2. Uneven gravitational pull of the moon and the Sun.
What are the two factors that causes the precession of Earth?
The orbits of Earth and moon are not on the same plane causing the gravitational imbalance.
2. Uneven gravitational
pull of the moon and
the Sun.

11. Uneven gravitational pull
Precession happens because moon’s orbit is tilted from the Earth’s elliptical plane

12. Precession is similar to a spinning top.

13. What is our current North star?
Earth’s current northern star is Polaris. Thousands of years from now it would be Deneb.
Earth’s axis

14. Constellations-group of stars forming a shape.
Thuban
(Alpha draconis)
Polaris
Vega
Now is a great time to sleep out under the stars!  Looking for summer constellations in the in the northern hemisphere is a great way to spend a warm summer night and the place to start your search is the Summer Triangle.
The Summer Triangle is made up of three bright stars that are in three separate constellations and are all inside of the Milky Way  – the bright band of stars that spans the night sky.  The Summer Triangle contains the stars Vega, Altair, and Deneb.
Let’s start with Vega.  Vega is part of the constellation Lyra.  Lyra is a small constellation that you will see directly overhead and is shaped like a parallelogram.  Vega is a bluish white star that is triple the size of our Sun and one of the brightest stars in the night sky.  It should be easy to find.
Deneb
Constellations-group of stars forming a shape.

15. Polaris
The Big Dipper is an asterism that makes up part of the constellation of Ursa Major (The Big Bear). It is seen here at the lower left of the image. The Little Dipper, part of the constellation of Ursa Minor (The Little Bear), is seen at the upper right. Polaris, the North Star, is at the end of the handle of the Little Dipper.The two stars at the end of the bowl of the Big Dipper, Merak and Dubhe, are called the "Pointer Stars" because a line drawn between them points to Polaris.
Hold your mouse cursor over the image to see the lines that make up the Big and Little Dippers, and the line from the pointer stars to Polaris.
The Big Dipper and Polaris play an important part in the story of the Underground Railroad which helped slaves escape their captivity in the southern states of the United States before the Civil War by fleeing north to Canada.
The folk song "Follow the Drinking Gourd" (another name for the Big Dipper) was a coded song that gave directions on the escape route from Alabama and Mississippi. While traveling on their long escape journey, they could always tell which way was north by the location of Polaris which they could find by the pointer stars.
The Big Dipper is a circumpolar asterism for most of the United States. This means it stays above the horizon all night long as it apparently rotates slowly counterclockwise during the night around Polaris due to the Earth's rotation. It is also comprised of very bright stars in an easy-to-locate pattern. The Little Dipper, on the other hand, is comprised of fairly faint stars that do not really stand out, except for second-magnitude Polaris.
This view shows what the northern sky looks like at about 3 am on June 21, the first day of summer, or 9 pm on September 21, the first day of fall. 
Now is a great time to sleep out under the stars!  Looking for summer constellations in the in the northern hemisphere is a great way to spend a warm summer night and the place to start your search is the Summer Triangle.
The Summer Triangle is made up of three bright stars that are in three separate constellations and are all inside of the Milky Way  – the bright band of stars that spans the night sky.  The Summer Triangle contains the stars Vega, Altair, and Deneb.
Let’s start with Vega.  Vega is part of the constellation Lyra.  Lyra is a small constellation that you will see directly overhead and is shaped like a parallelogram.  Vega is a bluish white star that is triple the size of our Sun and one of the brightest stars in the night sky.  It should be easy to find.

16. How long is Earth’s complete rotation on its axis?
Copy and answer the following questions.
How long is Earth’s complete rotation on its axis?
What is the direction of Earth’s rotation?
How long is Earth’s complete revolution?

18. Earth rotates counterclockwise.
Copy and answer the following questions.
How long is Earth’s complete rotation on its axis?
6. What is the direction of Earth’s rotation?
7. How long is Earth’s complete revolution?
Earth complete rotation takes 23 hours and 54 minutes
Earth rotates counterclockwise.
Earth’s complete revolution takes days

19. 8. The spinning motion of Earth’s rotation causes it to bulge at the ________.
North pole
South pole
Equator
hemisphere
Equator

20. 9. Earth rotation on its axis causes _____________. seasons weather
tide
day and night
day and night

21. precession d. revolution
10. Earth’s Northern star changes because of_____________. The cycle completes every 26,000 years.
rotation c. nutation
precession d. revolution
precession

22. northern star gravity seasons tide
11. NUTATION or the ½ degree wobbling around the precessional axis due to the uneven gravitational pull of the moon and the oblate shape of Earth affects which of the following?
northern star
gravity
seasons
tide

23. northern star gravity seasons tide northern star
12. PRECESSION or the rotation of the Earth’s axis changes our _____________ every few thousand years.
northern star
northern star
gravity
seasons
tide

24. 13. Why does Earth experience precession?
because the Earth revolves around the sun every 365 days
because of the movement of the circumpolar stars and Polaris
because the Earth is the third planet from the sun
because the plane of the moon’s orbit is tilted from the Earth’s elliptical plane

25. Vocabulary Words: Rotation- earth spins on its axis
- completes in 24 hours ( day and night)
2. Revolution –Earth spins around the Sun.
- completes in 365 days (year).
3. Precession – Earth’s axis spins/rotates.
- completes in 26,000 years.
- changes our northern star.
4. Nutation- irregularity ( zig-zag) in Earth’s precession by ½ or 0.5 degree.
- influences seasons.
5. Earth’s 23.5 degrees tilt on its axis is responsible for the seasons, not the distance from the Sun.