1. Planet Earth A Grand Oasis in the vastness of Space
Apollo astronaut Jim Lovell
Planet Earth is blue and there’s nothing I can do…
David Bowie

2. Planet Earth Third planet in the Solar System
An oblate spheroid (slightly squashed sphere) with approx. diameter km
Surface covered (75% – 80%) with water

3. Planet Earth Internal composition: core(s); mantle; crust
Moderate range of temperatures (approx. minus 20 oC to 40 oC)
Atmosphere of nitrogen, oxygen, water vapour, inert gases, CH4, SO2, O3, CO2

4. Planet Earth
Earth rotates on its axis in 23 h 56 min (a sidereal day) from west to east
Orbital period around the Sun days
‘Extra’ day every 4 years to maintain calendar (‘leap’ year)

5. Planet Earth
The orbital path of the Earth around the Sun is that of an ellipse
Perihelion (closest approach) occurs in early January
Aphelion (furthest point from the Sun) occurs in early July

6. Planet Earth
It is the tilt of the Earth’s polar axis is mainly responsible for seasons...

7. Planet Earth Polar axis tilted at 66.5 degrees to ecliptic Equator

8. Planet Earth
In summer, the northern hemisphere is tilted towards the Sun and so the Sun is higher in the sky and for longer each day.
In winter, the northern hemisphere is tilted away from the Sun and so the Sun is lower in the sky and for only a few hours.

9. Planet Earth
This angle is the latitude of the point
Equator
Ecliptic
Latitude is measured as an angle, north or south of the equator e.g 55 oN or 41 oS

10. Planet Earth
to observer’s zenith
observer’s horizon

11. Planet Earth
The pole star, Polaris, lies directly above the Earth’s north pole (well, almost!).
We can easily show using geometry that the angle of elevation of Polaris is equal to the latitude of the observer.
Polaris is a very useful navigational tool in that it also lies due north.

12. Planet Earth
To locate a point on the Earth’s surface, we also need its longitude.
This is the angular distance east or west of the Prime Meridian that passes through Greenwich in London.
e.g. 27 oE or 85 oW
Question 1. Find the latitude and longitude to the nearest degree) of:
Havana in Cuba c) Rome in Italy
Santiago in Chile d) Helsinki in Finland

13. Planet Earth
The Earth is not a luminous source; it reflects light from the Sun and so from space exhibits phases (like the Moon)

14. Planet Earth
However, the Earth does emit light in the form of light pollution!

15. Planet Earth
The Earth spins through 360 degrees in (just under) 24 hours. It takes 1 hour to spin through 15 degrees and 4 min to spin through 1 degree