What causes the seasons to change? The first answer many people give when asked why the Earth gets cold in the winter and warm in the summer is because the Earth’s distance from the sun can vary during its orbit. Astronomers have carefully measured the distance between the Earth and Sun and have discovered that the Earth is closest to the Sun in January, and farthest away in July. Show But wait a second! January is the peak of winter in the Northern hemisphere, and July is the peak of summer. There is another problem with the distance/season misconception: Why is it that when it is summer in the Northern hemisphere, it is winter in the Southern hemisphere? Something else besides varying distances from the sun must be causing the seasons.
Eventually, humans figured out that the varying seasons were caused by the earth’s tilt in combination with its orbit around the sun. You might have learned that the Earth spins like a top. It does not spin straight up and down, though—it spins at a 23 ½ degree tilt. The imaginary line that the earth is spinning around on is called its axis. When the top of the Earth is tilted towards the sun, it is summer in the northern hemisphere. Since the bottom half of the Earth (the southern hemisphere) is tilted away from the sun, it’s winter there.  On around June 21st, the northern hemisphere is at its max tilt towards the sun. This is called the summer solstice. This is also the longest period of daylight of the year in the northern hemisphere. On around December 21st, the Northern hemisphere is at its max tilt away from the Sun, which is known as the winter solstice and the shortest period of daylight. June 21st is the winter solstice for the southern hemisphere, and December 21st is its summer solstice. Just think about it: kids in Australia get to enjoy long summer days and winter holidays at the same time! In addition to solstices, our planet also experiences equinoxes. During its journey around the sun, the Earth reaches two points in its orbit where the tilt isn’t towards or away from the sun. The length of day and night are equal. These are called the equinoxes. On about March 21st, it is the spring equinox in the northern hemisphere, and the fall equinox in the southern hemisphere. On about September 21st, it is the spring equinox in the southern hemisphere and fall equinox in the northern hemisphere. The tilt correctly predicts the seasons, but how does the tilt cause warmer or colder temperatures? You can see for yourself! How does the tilt of the Earth cause the seasons?
The number of squares you count will vary depending on the size of your globe, graph paper squares, and flashlight. When you moved the flashlight over the surface of the globe, you probably noticed that the circle of light emitted by the flashlight was brighter and rounder near the equator. The circle of light became bigger and not as bright as you moved it towards the poles. There should be more graph paper squares in those circles. The light tracings also should start to look less like circles and more like stretched-out ovals. When you moved the flashlight along the middle part of your globe’s southern hemisphere, you were likely to notice that the circle of light was not as bright as it was in the northern hemisphere. When you got to the bottom of the globe, the light from the flashlight shouldn’t have reached the globe’s South Pole at all. In addition to demonstrating how seasons are caused, this experiment shows why some parts of the earth are warmer than others year-round. Remember that the flashlight always emits the same amount of light. When the light shines on the equator, the circle is bright and small, meaning lots of sunlight is concentrated in a small area. This is why the parts of the Earth near the equator are hot and have tropical vegetation. As you moved the light along the curve of the Earth towards the middle of either hemisphere, the same amount of light was spread out over a larger area. These parts of Earth’s surface get only a medium amount of light energy, explaining why these parts of the Earth are not as warm as parts located near the equator. Your light tracings near the poles were the biggest, meaning the sun’s light was spread very thin. That is why the North and South Poles are so much colder than the equator. The Earth’s tilt creates seasonal differences in light intensity. Since the northern part of the Earth was tilted towards the sun, the light circles were smaller and brighter. This causes these parts of the Earth to be warmer during the summer. By the time your light reached the North Pole, the light circle was bigger (meaning the light is more spread out), but since the pole was tilted toward the light, it can still experience daylight in the summer. When you shined the light toward the South Pole, it probably didn’t reach the South Pole at all because this pole is tilted away from the sun during the winter. This is why the poles experience almost total darkness in the winter. Disclaimer and Safety Precautions Education.com provides the Science Fair Project Ideas for informational purposes only. Education.com does not make any guarantee or representation regarding the Science Fair Project Ideas and is not responsible or liable for any loss or damage, directly or indirectly, caused by your use of such information. By accessing the Science Fair Project Ideas, you waive and renounce any claims against Education.com that arise thereof. In addition, your access to Education.com's website and Science Fair Project Ideas is covered by Education.com's Privacy Policy and site Terms of Use, which include limitations on Education.com's liability. Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety. If you’ve ever wondered what causes seasons on the Earth, you’ve come to the right place. In this article, we’ll give you different definitions of the seasons and explain why our planet has seasons at all. ContentsHow many seasons are there in a year?A season is a period of the year distinguished by particular weather conditions, temperature patterns, and the amount of daylight hours. The number of seasons depends on the geographical location and cultural traditions of the region you’re in. In temperate and subpolar regions of the Earth four seasons are generally recognized: spring, summer, autumn, and winter. Some South Asian calendars use six seasons instead of four. For instance, the Hindu calendar has the following seasons: Vasanta (spring), Greeshma (summer), Varsha (monsoon), Sharad (autumn), Hemanta (early winter), and Shishira (late winter). Many tropical regions only have two seasons: the rainy season and the dry season. When do the four seasons begin?There are two main approaches to defining the dates of the seasons: meteorological and astronomical. According to the meteorological approach, each season includes three months and begins on the first day of a three-month period. So, for the Northern Hemisphere, meteorological spring begins on March 1, summer on June 1, autumn on September 1, and winter on December 1. According to the astronomical definition, each season begins either on a solstice (when the Sun reaches the most southerly or northerly point in the sky) or on an equinox (when the Sun passes over the Equator). In the Northern Hemisphere, astronomical spring correlates with the March equinox, summer – with the June solstice, autumn – with the September equinox, and winter – with the December solstice. Because of leap years, dates of equinoxes and solstices can shift by a day or two. Why do we have seasons?Many people think that seasons change due to the elliptical orbit of our planet: when the Earth is closer to the Sun, the weather gets warmer, and when it’s farther away, temperatures drop down. However, the Earth’s orbit is nearly circular, so it has little effect on the weather and temperature patterns. The real reason behind seasonal variations is the Earth’s axial tilt, also known as obliquity in astronomy. Our planet’s axis of rotation is tilted at an angle of about 23.5 degrees relative to the orbital plane. Most probably, the tilt was caused by a collision with another planet about the size of Mars. Although the axial tilt does not change over the year, the Earth's orientation with respect to the Sun continuously varies as we revolve around our star. Thus, when one of the Earth’s hemispheres is oriented towards the Sun, it gets more hours of daylight, and we experience spring and summer; when it is tilted away from the Sun, it gets colder, and we get autumn and winter. How are seasons different in the Northern and Southern Hemispheres?The Southern Hemisphere seasons are opposite to the seasons experienced above the Equator. When it’s winter in the United States, it’s summer in South America; and when the spring season comes to Europe, autumn starts in Australia. As you now understand, it happens because the Northern and Southern Hemispheres are tilted toward the Sun at different times of the year. Do other planets have seasons?Every planet in the Solar System has seasons because the rotational axes of all eight planets are tilted. However, seasons on other planets are quite different from the Earth’s seasons. Let’s take Uranus as an example. This planet is tilted at nearly 98 degrees, so its rotational axis is almost parallel to its orbital plane. Moreover, it takes Uranus 84 Earth years to complete one orbit around the Sun. As a result, the ice giant has 21-year-long seasons; during the winter-summer seasons, the winter side of the planet doesn’t see the Sun for 21 Earth years. The rest of the planets are no less bizarre: for instance, Venus’ seasons are shorter than its days, and on Mercury, you can’t even tell when one season ends, and another begins. Now you know why we experience seasons on the Earth. 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What causes the seasons to change on Earth
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