Why does the length of day and night vary over the year?

Question

is it something to do with the June and december solstice? or the equinox?

Answer 1

timespiral has a good suggestion: do a demonstration with a globe and a light. Technically, you should make the globe orbit around the sun instead of vice-versa, but either way you can see how the amount of light on the northern and southern hemispheres varies in the course of the year.

Here's a way that you can think of the effect that may make it easier to understand. This is not what is ACTUALLY happening, but what we see from the earth is the same AS IF this were actually happening:

Imagine that the earth is not moving through space, but is simply spinning on its axis. (Its axis should be vertical.)

Meanwhile, imagine the sun at a significant distance from the earth, and at the same elevation as the earth. That is, the sun is directly "above" the equator. (An ant on the equator of the globe would see the sun pass directly overhead as the earth spins. An ant on either of the poles could just barely see the sun on the horizon.)

This describes the situation at the equinoxes (roughly March 21 and Sept. 21, the beginning of spring and fall).

Now imagine the sun moving upward (north of the equator). This is what we see during the spring. The sun doesn't actually move toward the north pole; rather the pole's orientation to the sun changes as the earth moves around the sun. But the VIEW from the earth (for a person who is not using fancy instruments) is the same as if the sun were moving northward.

Now as you picture the sun moving to the north, you can see that it is lighting a larger percentage of the northern hemisphere (more than 50%) and a smaller percentage of the southern hemisphere. So as the earth rotates, people in the northern hemisphere are viewing the sun for more than half of the 24-hour day. The days in spring are longer than 12 hours.

In fact, because the sun is "north of the equator," it is illuminating an area around the north pole 24 hours a day. As the earth turns, the north pole and its surroundings don't ever rotate into the dark part of the earth. On the other hand (or the other pole), the area around the south pole is constantly dark.

Six months later, the situation will be reversed, as the sun will be "south of the equator," the south pole's surroundings will have 24 hours of light and the north pole's surroundings will have 24 hours of darkness.

Meanwhile, the equator is always half light and half dark, so it always has (roughly) 12 hours of daylight and 12 hours of darkness. And for points between the equator and the poles? They experience something between the equal day & night (of the equator) and the 24 hours of light or darkness (as occurs at the poles). And the closer you are to the poles, the more seasonal variation you see in the lengths of the days.

Answer 2

The earth is inclined about 23 degrees on it's axis. As the earth orbits the sun the part of the earth in the light changes daily. In the summer, the earth is tilted toward the sun in the northern hemisphere but the reverse happens in the winter. It easiest to conceptualize this by taking a large ball and a lamp in a dark room. Now hold the ball steady at an constant angle and orbit the lamp. As you do this you'll see how the light changes on the ball.

Answer 3

It's not the distance from the Sun that changes the length of the day. The Earth is tilted on it's axis 23.5 degrees to the plane of the solar system - as it goes around the Sun, the length of the day on the equator stays the same, but sometimes one hemisphere gets more daylight, sometimes the other hemisphere does. That's why it's summer in South America during winter in North America. You'll have to look for a picture for it to make more sense.

Answer 4

The earth is on a 23 degree tilt so as the world turns you get a day as the earth goes around the sun it gets closer on one side of the equator then the other, example when it's 100* in North America it's 20* in south America think of it like a top but not spinning straight up and down but at an angle.

Answer 5

Its called EQUINOX. An equinox occurs twice a year (around 20 March and 22 September), when the tilt of the Earth's axis is inclined neither away from nor towards the Sun,

Answer 6

Disregard the previous.

Length of daylight per day varies because of how the axis of rotation of the earth is offset from the orbit of the earth around the sun. For the northern hemisphere, during the summer, the northern hemisphere is pointed more toward the sun.

Answer 7

Since Earth revolves around the Sun, the length of day/night depends on how far the Earth is from the Sun. The Earth's orbit around the Sun is not a perfect circle, rather it's an eclipse.

Answer 8

The earth's rotational axis (moving around its center) isn't parallel to its orbit axis (moving around the sun). This is why the poles have a very long night during the winter and a very long day during the summer.

http://en.wikipedia.org/wiki/Seasons

Answer 9

mind control, move to alaska, day is 6 months night is 6 months.