How do some countries like Norway have midnight sun?

The reason for the midnight sun (and long night at winter) is the axial tilt of the Earth. This is also the reason for the seasons.

Check out the links below.

Well, to provide an even simpler version of Jayy13's answer:

Here's an animation (the tilt is not perfect, but you'll get the point):

http://www.youtube.com/watch?v=ah_gXnjjdk4&feature...

Here's a zoomed out one:

http://www.youtube.com/watch?v=OUAkZ1FOAUQ

We think of the North Pole as "up" and the South Pole as "down", but in reality, the Earth is tilted. When the Earth then goes around the sun, and at the same time spins around itself, one side will always be in darkness. In the second animation, that is the South Pole, but six months later the Earth will have the other side towards the Sun (because it travels around the sun in circles), and the North Pole will be in darkness. This is also for countries near the Poles. The Northern line is called "the Polar Circle". If you go north of that line, the sun will be up all the time for three months, ordinary days for three months, all dark for three months, and then three months of normal days again. The further north you go, the more days the midnight sun (and midday moon) will last. At the North Pole, there will be no ordinary days, just six months of darkness and six months of light. The same with the South Pole.

This also causes the seasons, because when one half (or "hemisphere") has more sunlight than the other, it is summer there. So when it is winter on the Northern Hemisphere, the Southern Hemisphere is closer to the Sun, has more sunlight, and therefore summer.

As for what it looks like, the Sun will go from east to west, *not* set, but move from west to east, and so it goes, day after day.

Long story short, the tilt of the Earth is responsible for the length of our days and nights. As our location tilts away from the sun, the nights are longer, and when it tilts towards the sun the days are longer. However, this becomes problematic in the extreme north and south parts of Earth, near the poles.

In Antarctica, you essentially have one sunset and one sunrise a year. Once the sun rises and summer starts, the sun does not set below the horizon, ever. So even at 'night', you have sun, hence the name "midnight sun" for the sun shining even when we would normally consider it to be night. In the opposite season, the Arctic experiences this. At the poles, the midnight sun is usually referred to as a "polar day," and this constant daylight will last about six months.

Conversely, you have a phenomenon known as "polar night," where the sun never rises above the horizon. This happens when you are inside the Arctic/Antarctic Circles and the Earth is currently tilted away from the sun. Some places experience a twilight effect instead of total darkness, but very close to the poles you will have a very long night (six months if you're dead on the poles themselves).

Everywhere on Earth, the sun goes around the sky once in 24 hours in a big circle.

Most places, at night the ground gets in the way and you can't see it.

Above the Arctic Circle in summer, the circle is completely above the horizon. The sun rises up in the East, sets in the West, but never quite touches the horizon at midnight.