1. Hypothesis A :dependin of the position of the earth:Its true.The seasons are caused by a thing called "axial tilt", which basically means that the Earthwobbles. It wobbles very slowly, mind you: but it does wobble.When you spin a spinning top really fast, it starts out stable. Once the top has lost some energy,it starts to wobble a bit, then some more, and more, until its too unstable to keep spinning.The Earth does pretty much the same thing: while it spins around the sun, it spins around itself,and it wobbles. This causes one side of the Earth to be pointed at the sun at a better angle thanthe other, and that side gets more sunlight.More sunlight means more warmth, and that warmth is what causes summer. Likewise, the sideof the Earth thats at a shallower angle gets less sunlight, which means colder temperatures.Currently (November 2012) the Northern hemisphere is pointed away from the sun, whichmeans less sunlight in a day, causing winter. The Southern hemisphere, on the other hand, isexperiencing summer.Hypothesis B and C :because of the Earth rotation respect to the Sun: The length of day also shortens as the Earth revolves away from a summer solsticetoward a fall equinox, and the pole stops pointing toward the Sun. On the equinox, thelength of time that the centerpoint of the Sun spends above and below the horizon is thesame for the entire planet (but length of day is actually longer than night because theSun is a disc, not a point; equal day and night is called equilux). After that, nightcontinues to lengthen until the pole is always in darkness.So, getting back to the causes of seasons: when a pole points toward the Sun, itshemisphere experiences summer, while the opposite hemisphere (with the pole indarkness) has winter. The day of solstice is either the longest or shortest day of the yearfor everywhere on the planet - but its much longer or shorter at higher latitudes thanclose to the equator. What are the most common misconceptions about the causes of the seasons? That thecloseness of the Earth to the Sun is a cause, and that the solstice points match up withperihelion and aphelion. Both are false. Find out why these misconceptions exist here.
2. Hypothesis D: depending of the distance from the Sun What About Closeness to the Sun?"Summer is when the Earth is close to the Sun, and winter is when the Earth is fartheraway."The above statement is false, and one of the most common misconceptions about thecauses of the seasons. Where does it come from? The orbital path of the Earth around the Sun is an ellipse, ratherthan a perfect circle. At some points along its path, the Earth is closer to the Sun, and atother points farther away - that part is true. But often, diagrams that illustrate the ellipsewill exaggerate it to demonstrate their points, making it much more elongated than itactually is.From there, its reasonable to assume that something close to a heat source will bewarmer than something far from it, and since summer is warm and winter is cold, theseasons must be due to closeness to the Sun along the ellipse.When we sit close to a heat source, were warmer than when we sit farther away. Butstop and think about that for a moment too. Where are you warm? The parts thatdirectly face the heat source? What about the parts off to the side? Or do you have torotate back and forth a bit to warm up your sides and keep your front from getting tootoasty? The same thing happens for the Earth, as measured by the Suns angle ofincidence, which depends on the Earths axial tilt (see page 1).Another common misconception is that the solstice points happen when the Earth is atits closest to the Sun (perihelion) and at its farthest from the Sun (aphelion). This is alsofalse. The pattern of Earths axial tilt doesnt match up quite so neatly with the orbitalellipse. So What Does Closeness to the Sun Do?While the closeness of the Earth to the Sun is not a major cause of the seasons, it doeshave some influence on the temperature ranges of whichever season is happening ineach hemisphere. The Earth is closer when the southern hemisphere is having summer,and farther away when the southern hemisphere is having winter. Meanwhile, at thesame time, the northern hemisphere has winter when the Earth is close, and summerwhen its far. As a result, on average the southern hemisphere has much warmersummers and much colder winters than the northern hemisphere.
3. Hypothesis E: depending of the amount of energy the Sun emit.Our planet has an excellent source of energy: Sun. When solar radiation (i.e. the Sun’srays) reaches the Earth’s atmosphere, part of it is reflected back outwards and part of itis absorbed by the atmosphere. The rest reaches the Earth’s surface, where once again,part is reflected back and part is absorbed. The atmosphere and the surface (both landand ocean) are heated, and thus emit infrared radiation out towards space. The overalldifference between incoming and outgoing energy is known as the net radiation orradiation balance, and it can be stated for a region or for the planet as a whole.