(a) with the aid of a diagram, explain eclipse of the moon (b) State three charateristics of great circles (c) Outline three uses of great circles

Answer Details

(a) Eclipse of the Moon (lunar eclipse)

A lunar eclipse occurs when the Earth lies directly between the Sun and the Moon. The Earth blocks sunlight and casts its shadow on the Moon. This can occur only at full moon, when the Sun, Earth and Moon are aligned.

If the whole Moon passes into the dark central part of the Earth’s shadow, called the umbra, there is a total lunar eclipse. If only part of the Moon enters the umbra, the eclipse is partial. The Moon may appear reddish because some sunlight is bent through the Earth’s atmosphere into the shadow.

(b) Characteristics of great circles

• A great circle is formed by a plane passing through the centre of the Earth; it divides the Earth into two equal halves, called hemispheres.
• Great circles are limitless in number because they can be drawn in many different directions through the Earth’s centre.
• They are the largest possible circles on a globe. The Equator is a great circle; a complete circle formed by a meridian and its opposite meridian is also a great circle.

(c) Uses of great circles

• They help to locate places on the Earth’s surface, especially through the Equator and the system of latitude and longitude.
• They are used to determine directions and to plan routes in navigation.
• They show the shortest route between two places on the Earth’s curved surface, helping aircraft and ships save travelling time and fuel.

Examination reminder: For a lunar eclipse, remember the order Sun – Earth – Moon. For great circles, link their shape through the Earth’s centre to their navigation use: they provide shortest-distance routes.