GCSE Astronomy Topic 1 - Planet Earth

Oblate Spheroid

• Solid outermost layer of Earth, formed by tectonic plates

• Composed of iron, oxygen & silicon

• Continental crust ranges from 8km - 70km, whilst oceanic crust is ~8km

• Approx. 20°C

• 80% the volume of Earth

• The rock is hot enough to melt, however due to pressure, it stays a solid

• Contains convection currents of magma

• 2900km thick

• 1400°C - 3000°C

• Formed of liquid iron & nickel

• Responsible for the Earth’s magnetic field

• 2900km thick

• 3500°C - 4000°C

• Hottest division, a sphere of liquid iron at the centre of Earth

• 1200km thick

• 5000°C - 6000°C

How far north / south a position is

How far east / west a position is

The line of latitude which is exactly 0° which splits Earth into the Northern & Southern Hemispheres

Lines of latitude where the Sun lies directly overhead at the zenith at least once a year, with the Tropic of Cancer lying 23.5N & Tropic of Capricorn lying 23.5°S

At the tropics, the temperatures are hotter & there tends to be a smaller difference in seasons

The poles are both lines of latitude 66° from the equator - the Arctic circle lies north & the Antarctic circle is south. In both circles, there is at least one day where the Sun does not rise or set

Points that lie 90° from the equator where the axis of the Earth rotates

An imaginary line that goes from one pole to another through the observer’s zenith

This is the agreed line of longitude of 0° that goes through the Greenwich Observatory in London

The atmosphere is constantly moving. The moving weather can block viewing in the sky. It also means that the atmosphere refracts light from the Sun differently. This causes nitrogen to scatter & produce the blue in our sky.

The blue sky means we cannot make observations during the day, severely limiting when we can make observations, especially in the Summer.

Atmosphere refracts light, so position & brightness of stars is not accurate. This also makes stars appear to ‘twinkle’

From manmade sources like streetlights, cars etc. which builds up lots of light & prevents viewing stars at night

This particularly builds up in cities / urban areas with lots of light sources