Earth-Sun Relations and Seasons
The earth receives almost all its energy from the Sun"s radiation. Sun also has the This cycle will carry on, creating the seasons that we experience on earth. The seasons are caused as the Earth, tilted on its axis, travels in a loop around the Sun each year. Summer happens in the hemisphere tilted. Some assume our planet's changing distance from the sun causes the change in the seasons. That's logical, but not the case, for Earth.
Well, Earth's axis is tilted The tilt doesn't really make one pole that much closer to the sun than the other pole, as the figure suggests. You could calculate this distance knowing the radius of Earth and the fact it is tilted The real significance of the tilt is the distance through the atmosphere that the sun's rays must travel see figure 2.
A ray entering the atmosphere directly overhead, or parallel to a vertical line from Earth's surface, passes through a distance of 1 atmosphere roughly km. The farther through the atmosphere a ray must travel, the more likely it is to be absorbed, reflected, or scattered by molecules in the atmosphere, which would reduce the intensity of energy received at the surface.
The Seasons Referring to figure 1, we see that on June the Northern Hemisphere is tilted towards the sun, and the sun's vertical rays are directly above The sun is high in the sky in the Northern hemisphere and hence more solar energy reaches the ground than in the Southern Hemisphere.
The Seasons, the Equinox, and the Solstices
Just the opposite occurs on December when the Northern Hemisphere is tilted away from the sun. The sun's vertical rays are directly above Now it is summer in the Southern Hemisphere. Where do the sun's vertical rays strike during the two equinoxes? Note that Earth's axis is always tilted in the same direction. It is because Earth is on opposite sides of its orbit that the Northern Hemisphere is towards or away from the sun.
If Earth's axis were not tilted, there really wouldn't be any seasons. Ice Ages Earth's temperature really does not have to decrease much for an ice age: There is one condition that is necessary. There must be substantial land masses in the high latitudes where ice sheets and glaciers can form.
If the land masses are available, the easiest way to have an ice age is to decrease the contrast between winter and summer.
Warmer winters means that it snows more, because warm air can hold more moisture. Cooler summers means less snow melts, and hence the glaciers can grow.
The Seasons, the Equinox, and the Solstices
Sun also has the most dominating influence on the changing climate of various locations on Earth at different times of the year. The Earth rotates about on a fixed plane that is tilted The Earth needs 23hrs 56mins to complete one true rotation, or one sidereal period, around the sun.
The solar day, on the other hand, is the time needed for a point on earth pointing towards a particular point on the sun to complete one rotation and return to the same point. It is defined as the time taken for the sun to move from the zenith on one day to the zenith of the next day, or from noon today to noon tomorrow.
The length of a solar day varies, and thus on the average is calculated to be 24hrs. In the course of the year, a solar day may differ to as much as 15mins.
There are three reasons for this time difference. Because of this, the sun appears to move proportionately at a constant speed across the sky.
The sun thus produces a daily solar arc, which is the apparent path of the sun"s motion across the sky. At different latitudes, the sun will travel across the sky at different angles each day. The rotation of the earth about its axis also causes the day and night phenomenon. The length of the day and night depends on the time of the year and the latitude of the location.
For places in the northern hemisphere, the shortest solar day occurs around December 21 winter solstice and the longest solar day occurs around June 21 summer solstice. In theory, during the time of the equinox, the length of the day should be equal to the length of the night. The average time the earth takes to move around the sun in approximately days. This path that the earth takes to revolve around the sun is called the elliptical path.
When the sun is moving down from above the celestial equator, crosses it, then moves below it, that point of intersection between the two planes is when the Autumnal Equinox occurs.
This usually happens around the 22nd of September.