1. The Earth in the Universe
Location, Rotation, Precession and Nutation

2. A few tidbits about our planet…
The diameter of the Earth at the equator is approximately 12,750 km.
The circumference of the Earth is 40,075 km..
The Earth has an estimated mass of × 1024 kg

3. Other facts…. The Earth is 93 million miles from the sun.
The Earth is the third planet from the sun.

4. Even more….
The Earth is made up mostly of the elements iron, oxygen and silicon.
The Earth is considered to be a terrestrial planet. This means it has a core and a rocky surface.
The Earth is broken into large pieces called tectonic plates.

5. Where is the Earth located?
Earth is the third planet from the Sun in our solar system.

6. How does our Earth compare?
Earth is the largest of the terrestrial planets.
Earth is fifth largest of the eight planets.

7. Where is our solar system located?
Our solar system is located in the Milky Way Galaxy.
The Milky Way is part of a cluster of about 30 other galaxies.

8. More about our galaxy
Zoom through our galaxy

9. Review….. The universe is made up of many galaxies.
Galaxies are made up of many stars.
Some stars have planetary systems similar to our solar system.
Earth is a satellite planet of one particular star…. our Sun.

10. Building Our Milky Way
Let’s understand our galaxy by building it.

11. Building Our Milky Way The central bulge is at the center.
Spiral arms are around the central bulge. They contain mostly blue stars, gas and dust.
The Earth is located in one of the spiral arms.
There are blue stars and red stars in our galaxy.
Blue stars are young and hot stars.
Red stars are old and cool stars.

12. Is the Earth round? Technically, Earth is an oblate spheroid.
It is wider at the equator than at the poles.
This is caused by the rotation of the Earth on its axis.

13. So what is this axis thing you speak of?

14. Earth’s axis
The Earth’s axis is an imaginary line that runs through the center of the Earth from the north pole to the south pole.
The Earth is “tilted” with relation to this imaginary line 23.5⁰

15. Motion on the Earth’s Axis
One “spin” of the Earth about its axis is called a rotation.
One rotation takes 24 hours to complete.
This is what makes a “day”.

16. Some visuals about Earth’s rotation
Day and Night and Earth's Rotation - YouTube

17. Summary about Earth’s Rotation
The Earth rotates on an imaginary axis.
One rotation about the Earth’s axis takes 24 hours. This is called a day.
Rotation about the Earth’s occurs from west to east. (Counter clockwise)
Earth’s rotation is the cause for day and night.

18. What happens when the direction of the axis changes?
The change in the direction of the Earth’s axis is called precession.
The angle remains the same.
This will affect the stars near the poles
Does not change the seasons as long as the 23.5⁰ tilt stays the same.

19. Precession Illustrated

20. Wobble baby…..
Let’s check it out….. Ooppsss…. Wrong wobble!!!!

21. What is wobble and how does it relate to precession?
The “wobble” about the precessional axis is called nutation.
Nutation is a change in the angle of tilt by ½ ⁰ one way or the other. Results in the tilt either being 23⁰ or 24⁰.
This occurs over an 18 year period.
This is due to the Moon.
This causes a slight change in the seasons.

23. Barycenter

24. Now… let’s explain what barycenter is...
A barycenter is the point between two objects where they balance each other.
Its kind of like the center of gravity.
The center of gravity is the point in the middle of all the material that makes up an object, mass.

25. Center Point of Gravity
A ruler
A sledge hammer

26. Center Point of Gravity and Barycenter
When a moon orbits a planet, or a planet orbits a star, both bodies are orbiting around a point that lies outside the larger body.
The moon does not orbit the exact center of the Earth, but a point about 1710 km below the Earth’s surface.
The sun is not stationary in the solar system. It moves as the planets tug on it, but it never gets too far from the solar system barycenter.