How do you explain the cause of seasons?
That means that during part of the Earth's orbit, the northern hemisphere is leaning toward the Sun, so it gets more sunlight, while the southern hemisphere is leaning away, so it gets less sunlight. Six months later, the situation is reversed. In-between these extremes, the Earth's axis isn't exactly toward or away from the Sun, but rather is tangent to its orbit, so both hemispheres get similar amounts of sunlight.
When a hemisphere gets more sunlight due to the tilt, it is summer. When it gets less, it is winter. In-between, it is spring or fall. The cycle is the same in each hemisphere, only 6 months apart.
The Earth has a tilt of 23.5 degrees relative to the "ecliptic plane" (the imaginary surface formed by it's almost-cicular path around the sun). The tilt toward the sun is maximized during Northern Hemisphere summer in late June (the "summer solstice"). At this time, the amount of sunlight reaching the Northern Hemisphere is at a maximum.
In late December, on the date of the "winter solstice", the Earth's tilt away from the sun is maximized, leading to a minimum of sunlight reaching the Northern Hemisphere. The seasons, of course, are reversed in the Southern Hemisphere.
During the winter, cold air masses build up over North America, Europe, and Asia, due to the low intensity of sunlight. The oceanic air masses are much less affected by the seasons because circulations in the upper ocean replenish warm surface water if it has been ...more