What causes seasons?
Seasons are broadly characterized by the difference in average temperature and the length of day
Intuitively, it may seem that the varying distance of Earth from Sun causes seasons.
But in fact, the maximum difference of this distance is just about 3%.
The real cause of seasons is the tilt of Earth’s rotational axis relative to the plane of revolution.
When the Northern Hemisphere is tilted towards the Sun, it has longer days, receives more
of the Sun’s rays and the Sunlight hits more directly.
This happens around June of every year when the Northern Hemisphere has summer and Southern
hemisphere has winter.
相反 在十二月左右 北半球远离太阳 因此
Conversely, around December, Northern hemisphere is tilted away from the sun, thus experiencing
These extremes, when the poles are either farthest or closest to the Sun, are called
Solstices when we have the longest days or nights.
During late March, both the hemispheres are at equal distance from the Sun, and thus have
equal length of day or night.
This is called an equinox and it marks the beginning of spring for Northern hemisphere
and autumn for Southern hemisphere.
同样 在九月末 还有一个秋分来划分另外两个季节
Similarly, in late September we have another equinox heralding the other two seasons.
Note that Solstices are not the positions when Earth is closest or farthest from the
In fact Earth is closest to the Sun in January.
而且 倾斜角在一年里是恒定的 它要过很长一段时间才会改变
Also, the axial tilt which is constant throughout a year, does change over long periods of time.