Tomorrow is the Equinox, when the amount of daylight and the amount of darkness will be equal. It's the first day of Spring.
The seasons are NOT caused by the Earth getting closer or further away from the Sun. There ARE times when we are a little bit farther away from the Sun; that happens during the summer in the Northern Hemisphere, so that can't be the cause of winter. Also, the seasons are the opposite in the Southern Hemisphere - right now in Australia they're getting ready for fall. And at the Equator, there aren't really any seasons at all. It's warm all of the time. If we had seasons because we got further away or closer to the Sun, then the whole Earth would have the same seasons.
The reason we have seasons is because the Earth is tilted. This means that during some parts of the year, your hemisphere is pointed towards the Sun, and at other parts, it's pointed away. When your hemisphere is pointed towards the Sun, more sunlight falls on each square meter. This makes it warmer and brighter. You've probably noticed that summertime is not only warmer, but brighter too. Now you know why!
When your hemisphere is pointed away from the Sun, less sunlight falls on each square meter. So it's colder and not as bright. That's why even a sunny winter day isn't as bright as a summer's day.
In addition, because of the tilt, during the winter time your hemisphere spends more time in the dark shadow of the Earth on the side opposite from the Sun. That means that the night time is longer. But it's the opposite in the Summer. So right now, every night is a little bit shorter and each day is a little bit longer, about 2 minutes on average. Nights keep getting shorter and days keep getting longer until one day, night is equal to day. "Equi" means "equal" and "nox" means "night". So the equinox is when the day and night are equal in length. After tomorrow, days will be longer than night. They will keep getting longer until the Solstice, which I'll talk about in June.
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