THE SUN AND ITS FAMILY

« period of revolution round the Sun, a period we call a year. 2.The seasons The Earth does not spin upright in space as it travels around the Sun.

That is, its axis is not perpendicular to the plane of its orbit.

Its axis is tilted at an angle of 23 and a half degrees. The Earth's axis is always tilted in the same direction in space. This means that, as the Earth travels each year around the Sun, the axis is tilted alternately towards, then away from the Sun. Naturally, when the northern hemisphere is tilted towards the Sun, the southern hemisphere is tilted away; and vice versa. The tilt of the Earth's axis has a marked effect on the climate in most parts of the world, creating what we call the seasons. There are four main seasons: summer, autumn, winter and spring. The temperature varies in each season, depending how much a place is tilted towards or away from the Sun. It is midsummer in a place when it is tilted most towards the Sun.

It is midwinter when the place is tilted most away from the Sun.

In the northern hemisphere mid-summer is on June 21st and midwinter is on December 21st.

In the southern hemisphere midsummer is on December 21st and midwinter on June 21st. Between summer and winter is autumn, marked by a point in the Earth's orbit when the axis tilts neither towards nor away from the Sun.

And between winter and summer is spring, marked again by a point at which the Earth's axis tilts neither towards nor away from the Sun.

These points in the Earth's orbit are known as the equinoxes because then the lengths of day and night are equal throughout the world.

In the northern hemisphere the autumn equinox occurs on September 23rd and the spring equinox on March 21st each year.

Again, the seasons are reversed in the southern. »