On the Earth, a pivoted magnet will swing round to point roughly north-south and, if it is free to tilt, will take up an inclined position with the northern end pointing downwards in the northern hemisphere and upwards in the southern. Such a magnet can be used to plot the direction of the Earth’s magnetic […]

The interiors of the planets arc totally inaccessible to direct observations. The deepest bole drilled into the Earth goes to a depth of about l0 km, just a small fraction of the 6378km distance to the centre. Information about the interior must therefore come from indirect methods and in practice the most important method by […]

The best known part of the Solar System is, naturally enough, that part of it nearest to the Earth. Mercury, Venus, the Earth and Mars are known as the TERRESTRIAL PLANETS, but only because of their position in the inner Solar System, not because they are just like the Earth. The Moon, by comparison with […]