The tilt of the Earth can be attributed to the stabilizing effect of the Moon. The tilt of the Earth's rotation axis is part of what allows an appropriate climate for Earth to support life. By altering what portions of the Earth get the majority of incoming sunlight , no region on Earth is allowed to heat to extreme temperatures. A common misconception is that seasons are caused by the Earth moving farther or closer away from the Sun.
The first day of summer, or the summer solstice, occurs when the Northern Hemisphere is maximally facing the Sun. That is why we have day and night, and why every part of Earth's surface gets some of each.
Long, long ago, when Earth was young, it is thought that something big hit Earth and knocked it off-kilter. So instead of rotating with its axis straight up and down, it leans over a bit. By the way, that big thing that hit Earth is called Theia. It also blasted a big hole in the surface. That big hit sent a huge amount of dust and rubble into orbit. Most scientists think that that rubble, in time, became our Moon. When the sun is overhead, the light is falling straight on you, and so more light and more heat hit each square centimeter of the ground.
When the sun is lower in the sky, the light gets more spread out over the surface of the earth, and less heat per square centimeter can be absorbed. Since the earth's axis is tilted, the sun is higher when you are on the part of the earth where the axis points more towards the sun, and lower on the part of the Earth where the axis points away from the sun.
For the Northern Hemisphere, the axis points most toward the sun in June specifically around June 21 , and away from the sun around December This corresponds to the Winter and Summer Solstice solstice is Latin for "the sun stands". For the Southern Hemisphere, this is reversed. For both hemispheres, the earth is 90 degrees away from the sun around March 21 and then again around September This corresponds to the Fall and Spring Equinox equinox is Latin for "equal night".
Everyplace in the world has about 12 hours of daylight and 12 hours of night. Day and night are not exactly of equal length at the time of the March and September equinoxes. The dates on which day and night are each 12 hours occur a few days before and after the equinoxes. The specific dates for this occurrence are different for different latitudes.
On the day of the equinox, the geometric center of the Sun's disk crosses the equator, and this point is above the horizon for 12 hours everywhere on the Earth. However, the Sun is not simply a geometric point. Sunrise is defined as the instant when the leading edge of the Sun's disk becomes visible on the horizon, whereas sunset is the instant when the trailing edge of the disk disappears below the horizon. At these times, the center of the disk is already below the horizon. Furthermore, atmospheric refraction or bending of the Sun's rays cause the Sun's disk to appear higher in the sky than it would if the Earth had no atmosphere.
Thus, in the morning, the upper edge of the disk is visible for several minutes before the geometric edge of the disk reachs the horizon. Similarly, in the evening, the upper edge of the disk disappears several minutes after the geometric disk has passed below the horizon.
For observers within a couple of degrees of the equator, the period from sunrise to sunset is always several minutes longer than the night. This being said, the Earth is at its closest point distance wise to the Sun in January called the Perihelion and the furthest in July the Aphelion. But this distance change is not great enough to cause any substantial difference in our climate.
This is why the Earth's Near June 21st, the summer solstice, the Earth is tilted such that the Sun is positioned directly over the Tropic of Cancer at This situates the northern hemisphere in a more direct path of the Sun's energy. What this means is less sunlight gets scattered before reaching the ground because it has less distance to travel through the atmosphere.
In addition, the high sun angle produces long days. The opposite is true in the southern hemisphere, where the low sun angle produces short days. Furthermore, a large amount of the Sun's energy is scattered before reaching the ground because the energy has to travel through more of the atmosphere.
Therefore near June 21st, the southern hemisphere is having its winter solstice because it "leans" away from the Sun. Advancing 90 days, the Earth is at the autumnal equinox on or about September 21st. As the Earth revolves around the Sun, it gets positioned such that the Sun is directly over the equator. Basically, the Sun's energy is in balance between the northern and southern hemispheres. The same holds true on the spring equinox near March 21st, as the Sun is once again directly over the equator.
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