1. Earth’s rotation and revolution Asteroids, meteoroids and comets

2. How do we know how big the Earth is?
Watch
starts at 1:13 to 4:06
Alexandria: links Greece and Egypt
40,075 km actual Earth’s circumference
Eratoshenes’s calculation: km
2piR = C=  R= 6263 km
TODAY WE MEASURE 6371 km

3. Earth= 4.54 billion years old
First life
3.8 billion-year-old
Age of universe: 13.7 bya
Mass = 5.97E24 kg; Earth is 76x heavier than Moon
Moon mass= × 1022 kg
Sun mass =1.99E30 kg = 333,000 x Earth’s mass
Earth- Moon distance: 384,400 km
Methods:
Rocks in the 4-5 Ga range may be dated by measuring ratios of isotopes of uranium/lead, rubidium/strontium, potassium/argon, argon/argon, and neodymium/samarium. One way to judge the reliability of a radiometric measurement is to compare the results of different measurement techniques for the same sample.
Pretty much the solar system was formed 4.5 bya then
Homo sapiens: years ago
How old is the sun? how do we know  dating technique with Rb
First star: ~ 200 mill years after big bang

4. Earth’s axis of rotation
Is 23.5o tilted
Earth rotates eastward toward the Sun
SUN
Good video to recap:
Recap:

5. How rotation differs from revolution?
The turning of an object around an imaginary axis running through it
E.g. Earth’s rotation takes 24 hrs
The rotation of an object around an external axis (e.g. another object)
E.g. Earth’s revolution around the Sun is days
Leap year anyone?

6. Watch: MIT video https://www.youtube.com/watch?v=Pgq0LThW7QA
When it is summer in the northern hemisphere, it is winter in the southern hemisphere. Why?
Watch: MIT video

7. If the Earth weren’t tilted on its axis, there would be no season
Reason for seasons
Answer: because of Earth’s tilt
In summer months: Northern hemisphere toward the Sun
In winter months: Northern hemisphere away from Sun
The opposite happens to Southern hemisphere
Satellites that orbit Earth, including the moon, do not always stay the same distance from Earth. Sometimes they are closer, and at other times they are farther away. The closest point a satellite comes to Earth is called its perigee. The farthest point is the apogee. For planets, the point in their orbit closest to the sun is perihelion. The farthest point is called aphelion. Earth reaches its aphelion during summer in the Northern Hemisphere. The time it takes a satellite to make one full orbit is called its period. For example, Earth has an orbital period of one year. The inclination is the angle the orbital plane makes when compared with Earth's equator.
If the Earth weren’t tilted on its axis, there would be no season

8. Asteroids
Small, rocky objects that never formed into planets
They also orbit the Sun
Most found in the asteroid belt between Mars and Jupiter
Some can have their own satellite/moon
Bill Nye- Can we prevent the next impact by an asteroid?
Ida
Dactyl

9. Piece of rock moving through space
Meteoroid
Meteor
Meteorite
Piece of rock moving through space
a burning meteoroid as it enters the Earth’s atmosphere
a fragment of a meteor fallen to earth.
1st video to 2:25 min

10. A- Metorite B- Meteroid C- Meteor D- Asteroid
What do we call a rock that is…?
____Found between Mars and Jupiter?
____Travelling through space
____Burnt up in Earth’s atmosphere
____the space rock that reaches Earth’s crust
A- Metorite
B- Meteroid
C- Meteor
D- Asteroid

11. Shooting stars
Meteor Shower
are actually not stars but meteors as they burn up in Earth’s atmosphere leaving behind trails
Occurs when Earth passes into the path of debris left behind by a comet
These debris burn up in Earth’s atm. creating streaks of light in the sky
As a comet travels close to the Sun, it heats up and part of the comet vaporizes. After a comet has orbited the Sun many times, a lot of small pieces of the comet are left along the comet's path. A meteor shower happens when Earth passes through the path of a comet. When this happens, the bits of comet debris, most no larger than a grain of sand, create streaks of light in the night sky as they burn up in Earth's atmosphere. Bits of debris which enter Earth's atmosphere are called meteors. On any night, there are several small meteors which shoot across the sky. However, during a meteor shower, tens to hundreds of meteors can be seen each hour. Many of these meteor showers can be predicted and occur at the same time each year.
(Ha!)

12. Pingualuit meteor crater in Quebec

13. Comets Objects made of dust, ice, rock, and gas
The Sun’s wind pushes gases and particles away from the comet creating a tail
A comet has 2 tails: dust tail and gas tail

14. End

18. Solstices Occur on June 21 and Dec 21
Solstice occurs when the Sun shine directly on one of the two tropics because the tilt of the Earth’s axis reaches its maximum angle compared to the Sun
During the June (summer) Solstice the rays of the Sun shine directly on the Tropic of Cancer; longest day
During the December (Winter) Solstice the Sun’s rays shine on the Tropic of Capricorn; longest night

19. Equinox
As the Earth moves around its orbit, it reaches two points during the year where the tilt of its axis causes it to be straight relative to the Sun.
Thus, the Sun will shine directly on the equator on Mar 20 and Sep 22