Changing of season

Changing seasons | National Oceanic and Atmospheric Administration

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In many parts of the United States, you might change your wardrobe with the seasons, grabbing a heavy coat in winter, while wearing only a light t-shirt in summer. Although ecosystems, plants, and animals cannot adjust their attire quite so easily, they have evolved to make changes that help them survive seasonal conditions caused by the rotation of the Earth around the sun.

Do you know the difference between meteorological and astronomical seasons? Astronomical seasons are based on the position of the Earth in relation to the sun, whereas meteorological seasons are based on the annual temperature cycle. The Earth’s annual trip around the sun forms the basis for the astronomical calendar in which seasons are defined by two solstices and two equinoxes. The Earth is tilted 23.5 degrees on its axis of rotation, and how the North Pole is oriented toward or away from the sun determines two of these astronomical dates. At the winter solstice, the North Pole is tilted away from the sun, whereas at the summer solstice, the North Pole is tilted toward the sun. The equinoxes occur halfway between these events when the sun’s path is aligned with the Earth’s equator. The dates shown describe the astronomical seasons for the Northern Hemisphere in 2022; the exact dates vary slightly from year to year. Meteorological seasons are broken down into groupings of three months in our civil calendar based on the annual temperature cycle. We generally think of winter as the coldest time of the year and summer as the warmest time of the year, with spring and fall being the transition seasons. In the Southern Hemisphere, the seasons are reversed where summer occurs when the South Pole is oriented towards the sun, and winter happens when the South Pole faces away. (NOAA Office of Education/Kaleigh Ballantine)

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Click to see this graphic for the Southern Hemisphere

Do you know the difference between meteorological and astronomical seasons? Astronomical seasons are based on the position of the Earth in relation to the sun, whereas meteorological seasons are based on the annual temperature cycle. The Earth’s annual trip around the sun forms the basis for the astronomical calendar in which seasons are defined by two solstices and two equinoxes. The Earth is tilted 23.5 degrees on its axis of rotation, and how the North Pole is oriented toward or away from the sun determines two of these astronomical dates. At the winter solstice in the Southern Hemisphere, the South Pole is tilted away from the sun, whereas at the summer solstice, the South Pole is tilted toward the sun. The equinoxes occur halfway between these events when the sun’s path is aligned with the Earth’s equator. The dates shown describe the astronomical seasons for the Southern Hemisphere in 2022; the exact dates vary slightly from year to year. Meteorological seasons are broken down into groupings of three months in our civil calendar based on the annual temperature cycle. We generally think of winter as the coldest time of the year and summer as the warmest time of the year, with spring and fall being the transition seasons. (NOAA Office of Education/Kaleigh Ballantine)

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Why do we have seasons?

The Earth is tilted 23.5 degrees on its axis, which affects the distribution of the sun’s energy across the surface of the planet. As the Earth orbits the sun every 365 ¼ days, the axis is always pointing in the same direction into space, with the North Pole toward Polaris, the North Star. Around June 22, the Northern Hemisphere is angled towards the sun, and receives the most direct radiation and the most energy. This is the start of astronomical summer in the Northern Hemisphere and winter in the Southern Hemisphere.

Six months later, in December, the Earth has completed half a revolution around the sun. The Northern Hemisphere is now angled away from the sun and receives less energy than the Southern Hemisphere; this is the beginning of winter in the Northern Hemisphere and summer in the Southern Hemisphere. From north to south, the results of the distribution of solar energy can be seen in changing vegetation, animal behaviors, temperatures, and day length.

Meteorological versus astronomical seasons

You may have noticed that meteorologists and climatologists define seasons differently from “regular” or astronomical spring, summer, fall, and winter.

Astronomical and meteorological seasons

Meteorologists and climatologists use a slightly different time scale for meteorological seasons than for astronomical winter, spring, summer, and fall. Why do meteorological and astronomical seasons begin and end on different dates? In short, it’s because the astronomical seasons are based on the position of the Earth in relation to the sun, whereas the meteorological seasons are based on the annual temperature cycle and help scientists track climate and weather trends.

Spring into science

Celebrate the season of spring with NOAA! From new graphics to educational resources, spring into science with us and check out our content.

Seasonal effects

Seasonal changes in precipitation and temperature affect soil moisture, evaporation rates, river flows, lake levels, and snow cover. Leaves fall and plants wither as cold and dry seasons approach.

These changes in vegetation affect the type and amount of food available for humans and other organisms. Animals in temperate and polar regions must find alternate food sources, move to warmer locations, or hibernate.

Beyond the big four

Though in the United States, we often think of the seasons as winter, spring, summer, and fall, but there are many different ways seasons change throughout the world, and even within the United States. Can you think of other annual climate events or ways to define seasons?

Groundhog Day forecasts and climate history

Even though he’s been forecasting since 1887, Punxsutawney Phil’s track record for the entire country isn’t perfect. To determine just how accurate he is, we’ve compared U.S. national temperatures with Phil’s forecasts. On average, Phil has gotten it right 40% of the time over the past 10 years.

EDUCATION CONNECTION

What are some ways that animals adapt to seasonal changes in your region? How does this compare to other areas? How do people adjust to the seasonal changes in their region? How do the seasons impact the use of energy in your community? The resources in this collection help educators encourage their students connect their own observations of the seasons to concepts in Earth science and biology.

Why Do the Seasons Change?

SCIENCE — Earth and Space

Have You Ever Wondered...

Why do the seasons change?
Why is there more daylight in the summer than in the winter?
Do all areas of the Earth experience the same seasons at the same time?

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Today’s Wonder of the Day was inspired by Daniel. Daniel Wonders, “Why do seasons change?” Thanks for WONDERing with us, Daniel!

It's been a long, cold winter in Wonderopolis, and we've had lots of fun in the snow. But we're looking forward to trading our hats and gloves for shorts and tank tops when the weather gets warmer.

But how do we know warmer weather is really on the way? Is there a chance it will stay cold and keep snowing all year?

Luckily, the answer to that question is "no." After winter is over, we know spring will come with warmer temperatures and lots of flowers. Then the weather will get hot in the summer before cooling off again in the fall. Cold weather will return as fall turns into winter, and the cycle will start all over again.

You may know you'll see lots of different kinds of weather over the course of the year, but have you ever wondered why the seasons change? The answers can be found in the way the Earth moves in relation to the Sun.

The Earth's axis is an imaginary line running between the north and south poles. Each day, the Earth makes one full rotation on its axis. This rotation takes 24 hours, which we call one day.

While the Earth is busy turning daily circles, it is also traveling along a giant oval path around the Sun. This path is called Earth's orbit. It takes our planet 365 days to make one complete trip around the Sun. In fact, that trip around the Sun is how we define one year.

As the Earth orbits the Sun, it is slightly tilted on its axis. The tilt means that, on any given day, the Earth is slightly pointed toward or away from the Sun.

Depending on where you're standing on Earth, there are times your half of the world (called a hemisphere) is pointed toward the Sun. At other times, your hemisphere is pointed away from the Sun. As the Earth travels around the Sun over the course of a year and the tilt of its axis points your hemisphere toward or away from the Sun, you experience the changing of the seasons.

Have you ever noticed that the sun doesn't set until close to bedtime in the summer? By the time winter rolls around, however, you're probably eating dinner when it's already dark outside. The amount of daylight your hemisphere receives also varies because of the Earth's tilted axis.

When the North Pole is tipped toward the Sun, the northern hemisphere receives more sunlight and experiences longer days. This period of longer days, warmer weather and more sunlight is commonly referred to as summer. But just because you're enjoying a nice, hot summer doesn't mean everyone on the planet is, too.

When the northern hemisphere is tipped toward the Sun, the southern hemisphere is tipped away. Although residents of the northern hemisphere may be headed to the pool, the southern hemisphere is experiencing shorter days with less sunlight. When it is summer in the northern hemisphere, it is winter in the southern hemisphere.

Imagine you live in Topeka, Kansas, and you have a friend who lives in Buenos Aires, Argentina. If you want to plan a visit to see your friend in July, you might not want to pack your flip flops and shorts. When it's summer in Kansas, it's winter in Argentina.

Locations near the equator tend to have warm weather year-round. This is because the tilt of the Earth affects them less dramatically. Regardless of whether the Earth is tipped toward or away from the sun, equatorial locations continue to receive more constant light and heat than locations with latitudes closer to the poles.

This is why it can be 12° F in Minnesota on a January day, while it's 70° F in Florida. Don't be fooled, though. Just because a location may not experience dramatic seasonal changes doesn't mean they don't have seasons, too.

Wonder What's Next?

You’ll need to let tomorrow’s Wonder of the Day really sink in — and watch your step while you’re at it!

Try It Out

What season is it where you live right now? Grab a friend or family member and explore what the seasons have to offer you by checking out one or more of the following activities:

What scents remind you of this season?

Freshly cut grass

Suntan lotion

What things do you play with, use or wear during each season?

Pumpkins

Diving boards

What foods or flavors remind you of the season?

Peppermint

Pumpkin pie

What things do you see during this season?

Snowmen

Flip flops

What noises do you hear during this season?

Leaves crunching under your feet

Sleigh bells

What is your favorite season of the year? Why? Take an informal poll of friends and family members. Is there a consensus favorite season? Come up with a pro and con list of things you like and dislike about each season. Use your list to discuss the seasons with friends and family members. How can you use your pros and cons to make the most of each season?
Keep your very own sunlight log! For a period of a week or two, record each day what time the Sun comes up and what time it sets. Based upon the data you collect, are the days currently getting longer or shorter? Does your data match up with what you learned in today's Wonder of the Day about the changing of the seasons? If it doesn't, keep measuring for a few more days or weeks. Share what you learn with your friends and family members.
Spring, summer, autumn or winter — each season provides its own unique delights for the senses. Imagine you are creating a welcome kit introducing each of our seasons to a visitor from a distant galaxy. Create a profile for each season using your five senses: smell, touch, taste, sight, and sound, so your intergalactic buddy knows what to expect during his extended stay on Earth. Here are some questions to help you get you started. Below each question are a couple of examples. Can you guess what season applies to each example?
Smell

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Wonder Contributors

We’d like to thank:

Ashley from WA
for contributing questions about today’s Wonder topic!

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Astronomical seasons

The four astronomical seasons that make up the year: spring, summer, autumn and winter begin when the center of the Sun passes one of the points on the ecliptic: the spring and autumn equinoxes, winter and summer solstices.

The main reason for the change of seasons is the tilt of the axis of our planet in relation to the plane of the ecliptic, that is, the plane of rotation of the Earth around the Sun. The Earth's axis is tilted from the plane of the ecliptic by 23. 44 degrees. If this angle were equal to zero, the seasons would never change on the planet, the length of day and night would be the same, and the Sun would rise above the horizon to the same height throughout the year.

The change of seasons is not only on Earth. Consider the planets of the solar system.

The nearest planets to the Sun, Mercury and Venus, are not suitable examples, since these planets have almost no inclination of the axis of rotation to the ecliptic. Mercury is 0.01 degrees, and Venus is 177 degrees (it is upside down), which can be equated to 3 degrees.

Mars is similar to our planet in many ways. The inclination of the axis of rotation of Mars relative to the plane of its orbit is 25.2 degrees, which is only slightly more than the earth. Seasonality is similar to Earth, but a little more pronounced. When observed at different times of the year, you can see how the Martian “caps” at the poles change, melting occurs.

Jupiter's axis of rotation is tilted only 3 degrees with respect to the plane of the orbit. On the gas giant, the climate is not seasonal and is constant throughout the year.

The tilt of Saturn's axis of rotation is 29 degrees, so the change of seasons on this planet is characterized by more pronounced changes in the amount of sunlight than on Earth, and, consequently, temperature. All four seasons on Saturn last approximately 7 years. Since the entire year of the ringed planet lasts 29earth years. Depending on the time of year, Saturn can change its color. In the year when the automatic interplanetary station "Cassini" first approached the planet, it was winter in the northern hemisphere and this part of Saturn had a blue tint. Now it is summer in the northern hemisphere. This phenomenon occurs due to the intensity of ultraviolet radiation, in winter it decreases, in summer it rises. Well, the most noticeable fact of the change of seasons on Saturn is, of course, its rings. It is they who, for an observer from Earth, will quickly answer the question: “What season is it now on Saturn?” The inclination varies depending on the time of year, since the rings lie in the plane of the planet's equator, which means they have an inclination to the ecliptic equal to 29degrees. When it is summer in the northern hemisphere, the planet turns the northern hemisphere and its rings towards the Sun, and therefore towards the Earth, when it is winter, we see the southern hemisphere. During spring and autumn, the rings become so narrow for the observer that it is difficult to see them. At the equinoxes, Saturn turns into a planet without rings. They disappear.

The angle of inclination of the axis of rotation of Uranus is 97.86 degrees - it lies on its side, so the planet has a specific change of seasons, not similar to our planet.

On Neptune, the axis of rotation is deviated by 30 degrees, so the change of seasons here is similar to Earth, but the distance of the planet to the Sun makes its own adjustments. A year on Neptune is almost 165 Earth years, and each season lasts 41 years. Summer began in 2005 in the southern hemisphere and will last until 2046.

Does the sun always rise in the same place? No. With the change of seasons, the direction to the point of sunrise also changes. On the winter solstice, the sunrise and sunset points are closest to the south direction, and on the summer solstice they are closest to the north.

Days of equinoxes and solstices

Astronomical spring has arrived on March 20, 2020 at 10:49 local time. At this moment, the center of the solar disk will cross the celestial equator and move from the southern celestial hemisphere to the northern one. The height of the Sun on the celestial sphere and, accordingly, the daylight hours will increase until the onset of astronomical summer. This day is called the spring equinox. The fact that the equinox came so early is not surprising - it was a leap year.

June 21, 2020 at 4 hours 44 minutes - astronomical summer. The sun, moving along its path, will move as far as possible from the celestial equator and reach the northernmost point. This day is called the solstice.

September 22, 2020 at 20:31 - astronomical autumn. The sun on this day, moving along its path in the celestial sphere, crosses the equator and passes from the northern hemisphere to the southern. This day is called the autumnal equinox: day equals night. After that, the night in the northern hemisphere of the Earth becomes longer than the day, and in the southern hemisphere of the Earth the nights become shorter. This astronomical season will continue until December 21st.

The days around the autumnal equinox are favorable for astronomers and astronomers. The long night and relatively warm weather make it possible to carry out astronomical observations comfortably from evening to morning, about 12 o'clock.

During the equinoxes, the terminator on Earth - the line separating the day and night sides of the planet - is vertical and connects the north and south poles. This can be seen in the photographs of our planet, which are made by artificial satellites.

December 21, 2020 at 17 hours 2 minutes - winter solstice. The sun, moving along its path, will move as far as possible from the celestial equator and reach the southernmost point. The northern hemisphere has the shortest day, while the southern hemisphere has the longest. This is the most favorable period for observing various celestial objects in the night sky, but winter cold and frequent inclement weather (in central Russia) do not allow full-fledged observations.

The material was prepared by Victoria Damm, UC Planetarium
Sources: astronomical calendar for the 2019/2020 academic year. Issue 70;
Stellarium program.

Why the seasons change | First day of summer | When spring begins

If you have ever wondered why the seasons change on Earth, our article will be useful to you. We will talk about what approaches exist to determine the seasons, and also explain why the seasons succeed each other.

How many seasons are there in a year?
When are the seasons?
Why does the seasons change on Earth?
How do the seasons differ in different hemispheres?
Are there seasons on other planets?

How many seasons are there in a year?

Season or season is a period of the year characterized by certain weather conditions, average daily temperature and length of daylight hours. The number of seasons in a year depends on your geographical location and the cultural characteristics of your region. In temperate and circumpolar regions, 9 are usually distinguished0066 four seasons : spring, summer, autumn and winter.

In some South Asian countries, the year is divided into six seasons instead of four. For example, the Indian calendar has the following seasons: spring, summer, rainy season, autumn, early winter and late winter. In many tropical regions, there are only two seasons : the rainy season and the dry season.

When are the seasons?

There are two main approaches to determining the time limits of the seasons: meteorological and astronomical.

According to the meteorological approach, each season consists of three months and starts on the first day of the first month. Thus, in the Northern Hemisphere, meteorological spring begins on the first of March, summer on the first of June, autumn on the first of September, and winter on the first of December.

According to the astronomical approach, each season begins either on the day of the solstice (when the Sun reaches its northernmost or southernmost point in the sky) or on the day of the equinox (when the Sun crosses the celestial equator). In the Northern Hemisphere, the beginning of astronomical spring is counted from the March equinox, the beginning of summer - from the June solstice, the beginning of autumn - from the September equinox, and the beginning of winter - from the December solstice. Due to leap years, the dates of the equinoxes and solstices may differ by one or two days each year.

Why does the seasons change on Earth?

Many people think that the seasons change each other because of the ellipticity of the orbit of our planet: when the Earth approaches the Sun, it becomes warmer, and when it moves away, it becomes colder. However, the Earth's orbit is almost circular and does not significantly affect the weather and temperature conditions.

The main reason for the change of seasons is the tilt of the earth's axis . The axis of rotation of our planet is tilted at an angle of about 23.5 degrees with respect to the orbital plane. Most likely, the axis of rotation tilted after the collision of the Earth with another planet about the size of Mars.

Although the tilt of the axis of rotation remains unchanged, the orientation of the Earth relative to the Sun is constantly changing as the Earth revolves around the star. When one of the hemispheres of the Earth is turned towards the Sun, spring and summer come in this hemisphere; the other hemisphere at that moment receives less sunlight, and autumn and winter come there.

How do the seasons differ in different hemispheres?

The seasons in the northern and southern hemispheres are opposite. When it is winter in North America, it is summer in South America; when spring comes to Europe, autumn comes to Australia. As you now know, this is due to the fact that the Northern and Southern Hemispheres face the Sun at different times of the year.