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whate causes seasons on earth ? 9
The Earth is tilted on its axis. 'Summer' (the warmest season) occurs when a hemisphere, either the northern hemisphere or the southern hemisphere, is tilted towards the Sun and thus receives more direct sunlight (the Sun is closer to the zenith and is above the horizon longer). A common misconception is that the seasons have to do with the Earth being closer to the Sun due to the elliptical nature of its orbit. The orbit is elliptical and the Earth is closest to the Sun [aphelion] in early January, farthest away [perihelion] in early July) this has a minor effect on the seasons, more important is the number of days and weeks the Sun is higher in the sky; near perihelion for the northern hemisphere (although the Sun is further away) the atmosphere has the opportunity to heat up more.

Twice during the year (spring and fall Equinox - around the 20th of March and September respectively), the Sun appears to circle more directly over the equator [the axis of the Earth is in a plane perpendicular to the orbit], and most areas of the globe receive similar amounts of daylight (the poles are exceptions with extremely long periods of the sun either above or below the horizon. From late December to late March, the Southern Hemisphere experiences 'summer' while the Northern Hemisphere experiences 'winter'. From late June to late September, the position is the other extreme, and it is summer in the Northern Hemisphere, winter in the Southern.

These yearly changes in insolation (incoming energy from the Sun) cause the seasons, in conjunction with the prevailing directional wind patterns, ocean areas, currents, and pressure systems which all affect the local climate.