I am trying to understand why it is warm in summer an cold in winter. I know it is sort of a dumb question and googling should have helped me, and that I did, but it I still couldn’t really understand.
Let us take only the northern hemisphere for our purposes. The same reasons will work for the opposite hemisphere.
What I gather is that the seasons are because of the tilt of the earth’s axis. In summer the northern hemisphere gets more sunlight and in winter it gets less. What is this ‘more’ and ‘less’ in terms of sunlight. Is it because of the more amount of time that the surface is exposed to the sun, or is it because the surface is closer to the sun on account of the tilt? Or both?
I understand that the sun’s rays have to pass through a larger/smaller ‘thickness’ of the atmosphere on account of the tilt and so the intensity of sunlight reaching the surface is less in winter and more in summer. Looking at it another way, is it not the same as saying that the distance between the surface and sun increases and decreases because of the tilt?
If it is because of the distance from the sun that increases and decreases on account of the tilt, then how much closer and farther, in terms of an actual scale like kms or meters, are we from the sun during the two seasons?
I am sure I can calculate that by applying some trigonometry, but I would like to be lazy because I am sur some of you on this board already have that figured out.
The tilt determines how directly sunlight hits the surface of the Earth. In the summer, the light hits almost perpendicularly. In the winter, it’s a much lower angle. So the same amour of light is spread over a larger area, resulting in cooler temperatures.
Let’s say that the earth wasn’t tilted. Let’s also consider a shaft of sunlight that passes through a 10 x 10 square and hits the earth.
At the equator of our non-tilted earth, that 10 x 10 shaft of light hits a 10 x 10 square on the earth’s surface.
Now, move up to the 45 degree latitude line. Now the surface of the earth is tilted 45 degrees away from the sun. Now that 10 x 10 shaft of light strikes a (roughly) 10 x 14 rectangle on the earth’s surface (because it’s tilted away). You’ve got the same amount of incoming energy spread out over 40 percent more area.
Now just tilt the earth so that the square where all of the energy is concentrated into 10 x 10 shifts with the seasons.
The question is already answered; more hours of sunlight, and it strikes more directly, in summer.
However, I wanted to point out that this can be rather easily understood if you actually use a globe. Almost all cheap globes sold at department stores and what not have the Earth tilted at more or less the right angle. Just sit in a room with a single, weak light source, like a small light or a candle, a few feet away, and move the globe so it’s northern “summer” and then spin it. Then move it so it’s northern “winter” and spin it. It is strikingly obvious how much more light there is, and how much stronger it is, during summer. (To anyone living within five or ten degrees of 45 north, it’s equally striking how remarkably far away from the Sun we are tilted in winter. It’s much more than you might intuitively imagine.)
Get a piece of paper, shine a light on it, and tilt it. Does it receive more light when the paper is perpendicular to the light, or at an angle? The earth is tilted, so in the summer the northern hemisphere is getting the light more “head on” and during winter we get it more “at an angle”. It’s a simple as that.
Distance has nothing to do with it. In fact, the earth is closer to the sun in the northern hemisphere’s winter and farther away in the summer.
You can probably do the math. The northern temperate zone gets many more hours of sunlight during high summer than the Tropic of Cancer, but where’s the higher temperature? (The North Pole is getting 24/7 daylight at the moment, but it’s still freezing.)
Let us say we have a heat source in a vaccuum. If I put a sheet of paper of the size you have mentioned at some distance from it say 10 cms. Since we are in a vaccuum, I am assuming that all the heat transfer is on account of radiation only. The paper will absorb the radiated heat and its temperature will rise by say x degrees.
Now I tilt the paper while maintaing the same position, so that the upper part is now tilte away from the source. Will the temperature on the upper part of the paper, that is tilted away from the source be lower than the portion that is not. If that is true, then why? The amount of radiated energy is still the same from the source. The area on which it is falling is still the same. Then what will cause the difference in the amount of energy absorbed?
Now if were to put some medium between the source and the paper, things would be different. The tilted portion being farther away would imply the radiation to travel thro more of the intervening medium and thus loose energy to it, leaving less to fall on the paper itself.
First of all, the Sun is 93,000,000 miles away, not 10cm. That means that the light rays that the Earth intercepts are very nearly parallel. So, the tilt of the Earth has a hues effect, as the “solid angle” of the light ray is spread over a much larger area.
Distance doesn’t matter here. Take your trusty piece of paper and look at it head on. It should measure 8.5"x11" and look like a regular piece of paper. Now turn it 90 degrees and look at it from the side. It should be under a millimeter and look something like a line.
Which orientation catches more light? Light per area (aka energy, aka heat) is entirely a function angle and not distance.
The amount of radiated energy is not the same after you tilt the paper. Because it is tilted, it is being hit with a smaller total amount of sunlight. The area of the paper is the same, but the amount of sunlight that the paper is blocking is smaller. Imagine if you tilted the paper ninety degrees so that it was edge-on to the sun. At that angle the paper would block almost no sunlight at all, and would not heat up much as a result. If you tilted the paper forty-five degrees, it would only block about 70% as much sunlight as if it was flat-on, and would also therefore not heat up as much as a piece of paper that was not tilted.