Schematic showing how the position of the Earth around the Sun gives rise to the seasons. The Earth's spin axis is tilted by an angle of 23.5 degrees. Summer begins in the northern hemisphere when the planet's north pole is pointed most directly at the Sun (summer solstice). When the south pole is pointed at the Sun, it is summer in the south and winter in the north (winter solstice). Spring and autumn occur at intermediate positions in the orbit, known as the equinoxes. At the start of winter in the north, the Earth is at its closest to the Sun, a point in its orbit known as perihelion. When farthest away, during northern summer, the corresponding point in the orbit is called aphelion. In addition to the 'astronomical' seasons, there are also the 'meteorological' ones. These are defined arbitrarily as three-month blocks beginning with (in the north) meteorological winter (Dec to Feb) and ending with meteorological summer (Jul to Sept).