Planet Earth

• A Grand Oasis in the vastness of SpaceApollo astronaut Jim Lovell

• Planet Earth is blue and there’s nothing I can do…

David Bowie

Planet Earth

• Third planet in the Solar System• An oblate spheroid (slightly squashed

sphere) with approx. diameter 13 000 km• Surface covered (75% – 80%) with water

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

Planet Earth

• Earth rotates on its axis in 23 h 56 min (a sidereal day) from west to east

• Orbital period around the Sun 365.25 days

• ‘Extra’ day every 4 years to maintain calendar (‘leap’ year)

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

Planet Earth

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

Planet EarthPolar axis tilted at 66.5 degrees to ecliptic

Ecliptic

Equator

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.

Planet Earth

Ecliptic

Equator

This angle is the latitude of the point

Latitude is measured as an angle, north or south of the equator e.g 55 oN or 41 oS

Planet Earth

observer’s horizon

to observer’s zenith

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.

Planet EarthTo 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:

a) Havana in Cuba c) Rome in Italy

b) Santiago in Chile d) Helsinki in Finland

Planet Earth

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

Planet Earth

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

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