Seasons

Source: https://www.exploringnature.org/db/view/1888

Our weather changes all year long – this is called the seasons. The seasons cycle from fall to winter to spring to summer every year. The seasons change because of two things:

1. How much direct sunlight a place gets during the year: When the sun is right over our heads, high up in the sky – that is called direct sunlight. That is the most sun an area can get. Direct sunlight is warmer than sunlight hitting the Earth at an angle. Here in the Northern half of the Earth (the Northern Hemisphere), we get the most direct sunlight on June 21st every year. This is the first day of summer.

2. How long the sun shines on one place during a day (day length): Longer days get more sunshine. The longer the day, the more time the sun has to warm us up. On June 21st – the first day of summer– we get more sun for the longest time than any other day all year.

The longest day length is called the summer solstice and is considered the first day of summer. In the Southern Hemisphere, it is the exact opposite! They experience the winter solstice on that day – the shortest day length of the year.

Figure 1.

How Does This Work?

The length of day changes all year. That is because the Earth is tipped 25^o on its axis (see picture). If the Earth stood straight up and down, we would have 12 hours of day and 12 hours of night all year round, everywhere on Earth. Because of the Earth’s tilt, the Arctic in the far north, in the summer is tipped toward the sun. So from March 20th to September 22nd the sun never stops shining in the Arctic. Yet even though it gets sunlight for six months of the year, it is still not as hot as places nearer the equator. This is because the sun does not shine on the Arctic directly overhead, but at an angle.

You would think that the hottest day in the Northern half of the Earth (Northern Hemisphere) would be on June 21st, but it really takes several weeks to warm the Earth. So it is usually July before we feel the warmest days. It also gets hotter all day as the sun “rises” in the sky. As with the seasons, even though the most direct sunlight is at noon, the day gets warmer and warmer until early in the afternoon.

The hottest place on record in North America is Death Valley, California, where it often reaches over 100^oF and once reached 134^oF on July 10, 1913. The coldest place on record in North America is Prospect Creek, Alaska where it reached -80^oFon January 23, 1971.

Figure 2.