20.8 Temperature and Heat Exchange Processes

20.8.2 Describe the temperature reference points of the centigrade scale used in New Zealand aviation.

The centigrade (Celsius) scale uses two main reference points:

• 0°C — the freezing point of pure water.
• 100°C — the boiling point of pure water at standard atmospheric pressure.

There are 100 equal temperature divisions (degrees) between these two reference points.

In New Zealand aviation, temperatures are normally expressed in degrees Celsius (°C).

Key point:
0°C = water freezes
100°C = water boils

20.8.4 Explain the factors that influence the amount of solar radiation received at the earth’s surface.

The amount of solar radiation reaching the Earth’s surface varies with several factors.

Angle of the sun

When the sun is high in the sky, its radiation strikes the surface more directly and is concentrated over a smaller area.

When the sun is low in the sky, the same amount of radiation is spread over a larger area, so heating is weaker.

This is why solar heating is generally stronger:

• Around midday than in the morning or evening.
• In summer than in winter.
• At lower latitudes than near the poles.