The difference between solstice and equinox, explained

Five things to know about autumnal equinoxes

After the autumnal equinox, the northern hemisphere of the Earth begins to tilt away from the sun, so nights will get longer and days grow shorter.

Why we have different seasons

Visualize just how exactly seasons come to be with this animation of the earth in relation to the sun, and see how earth's tilt determines our seasons.

Meteorological v. astronomical seasons, explained

Meteorologists and climatologists define seasons differently from “regular” or astronomical spring, summer, fall, and winter. Traditional seasons reflect the movement of celestial objects, known as the astronomical seasons; meteorologists mark seasonal change based on temperature averages.

Earth’s tilt and orbit cause the sun to create a figure-eight pattern

The shape—called an analemma—can be obtained by photographing the sun from the same location and time daily for a year. The Earth's eccentricity created the analemma's width, and its tilt shifts the sun's height in the sky over the seasons.

Is the sun aligned with Stonehenge right now?

Twice a year, during the longest day and night, the sun’s path aligns ever so gently with the ruins of Stonehenge. During the summer solstice, viewers can see the sun’s rise crest the central heel stone. The winter solstice sees the sun set across the site’s altar stone. Use this interactive to tour the historic site and check its current skyscape.

The winter solstice has been celebrated globally for millennia

From gatherings at Stonehenge in the UK to celebrations of the triumph of Mithra in Iran, cultures around the world have marked the shortest day of the year in a variety of ways for a very long time. Here are eight known to us today that endure.

Every eclipse is preceded or followed by another eclipse, separated by about two weeks and alternating between solar and lunar types.

While the sun, moon, and stars rise and set from east to west due to Earth's rotation, the moon's eastward revolution around the Earth causes its shadow to move from west to east during a solar eclipse.

The solstice has been celebrated globally for millennia.

Grasp the earth's orbit around the sun with this interactive

See why seasons exist with this interactive simulator. Toggle between different views of the earth in relation to the sun and watch as the earth's axis causes the sun to shine at different angles throughout the year, causing the weather to fluctuate and more. This simulator clarifies a process many take for granted.

The world's different calendars, explained

The calendar we use to mark the days, months, and year can feel set in stone, but the history of calendars shows these organization systems can and do change. Parse the fascinating, complex details of the Gregorian, Julian, Chinese, Hebrew, and many more calendars in this comprehensive, well-executed explainer video.

Why the sun's equator rotates once every 24.5 days, but the poles take over 34 days

Just like the Earth, linear speeds on the surface of the sun decrease from the equator to the poles. However, rotation time also appears to vary with depth, with the radiative zone beneath the convection zone rotating about once every 26.6 days. Measurement uncertainty has prevented measurement of the rotation of the solar core.

Although the moon passes between the sun and Earth each month, its orbit is tilted by five degrees, preventing Earth from experiencing a solar eclipse each month.

Some maps may incorrectly identify the boundaries of a solar eclipse's totality because they assume the Earth is a smooth surface.

What's the difference between weather and climate?

A five-minute TedEd video exploring the differences between weather and climate – what they are, how we predict them, and what those predictions can tell us.

Changes in Earth's orbital cycles influence the timing of ice ages

These cycles include changes in Earth's orbit shape, tilt, and wobble, all of which alter how much solar energy different parts of Earth receive over time. Due to orbital eccentricity, summers in the Northern Hemisphere last about 4.5 days longer than winters.

Over thousands of years, the frequency of solar eclipses is greatest around the Arctic and Antarctic Circles and lowest near the equator.

Watch the sunset at Stonehenge during the 2025 Summer Solstice

Each year, tens of thousands gathered at Stonehenge to witness the sun’s alignment with the stones during the solstice. Watch a replay of a lifestream of the event from 2025.

Daylight saving time, explained

Daylight saving time is supposed to help—but does it? Dive into the history, science, and consequences of this biannual aspect of American life (unless you're from Arizona or Hawaii).

How its uneven rotation produces the sun's 11-year cycle and flips its magnetic poles

While charged material rises and falls in the sun's convection zone, which induces magnetic fields, different latitudes rotate at different rates, making these fields increasingly turbulent. This builds to a critical point—the solar maximum—where magnetic field-driven events, such as solar flares, become more common before the field collapses and flips, restarting the cycle.

Solar eclipses are a cosmic coincidence because the moon is 400 times smaller than the sun but about 400 times closer to Earth, allowing it to block sunlight for those on Earth within its shadow.

Explaining why the Earth wobbles

Astronomers going back to Hipparchus in the 2nd century BCE have noticed our planet has a distinct wobble. More recently, scientists have observed that the Earth is 26 miles wider at the equator than from pole to pole. The wobble results from our...

Why meteorologists say summer starts June 1

There are at least two periods called summer: astronomical and meteorological. Astronomical summer mirrors the movement of celestial bodies and begins roughly around June 20, with the summer solstice. Meteorologists designate the beginning of June as the start of summer to make tracking weather patterns from year to year easier.

Because the half of Earth that faces the sun is larger than the area of the shadow cast by the moon during a solar eclipse, observers may experience a total, annular, or partial eclipse.

See images of modern Druids who visit Stonehenge to celebrate the solstice

At the summer solstice, crowds at Stonehenge range from white-robed modern Druids with staffs and antler crowns to revelers with ox-horn trumpets or hula hoops—scenes regularly documented by photographers.

How the ancients calculated Earth's size correctly

Watch this seven-minute video to hear Carl Sagan explain how ancient Greek polymath Eratosthenes correctly calculated the size of the Earth in the third century BCE. At some point, Eratosthenes noticed a discrepancy in the length of shadows cast in different cities during the summer solstice. This observation grew into a simple experiment that enabled Eratosthenes, the head librarian at the Library of Alexandria, to calculate the Earth's size precisely.

Visualize your city’s annual daylight map

Type in your town or region and see sunrise and sunset for each day of the year. A separate view shows the number of hours of day versus night for each day. Search a city far north like Oslo, Norway, and compare its graphs to one near the equator (like Singapore).

Compare various El Niño-Southern Oscillations using maps of atmospheric and ocean variables

Because the intensity of the phases in the cycle is sensitive to small variations in atmospheric and ocean conditions and depends on complex interactions between these two systems, no two El Niño or La Niña events are identical. This contributes to the variability in the length of each phase, which is why an ENSO can last as little as two years or as long as seven.

Why parts of the Earth are colder when the planet is closer to the Sun

The Earth orbits the Sun in an elliptical shape, and winter in the Northern Hemisphere occurs when the Earth reaches the point in its orbit closest to the Sun, known as perihelion. The lower temperatures result from the hemisphere tilting away from the Sun.

Aurora borealis and auroras australis do not always mirror one another

While the Earth's magnetic field is symmetric across the magnetic north and south poles in isolation, charged particles from the sun distort the field. If the angle of impact between the wave of particles and the Earth's field is such that the distortions are uneven, dissimilar geomagnetic storms and resulting auroras are produced in the northern and southern hemispheres.

Earth's smooth, continuous motion as it orbits the sun prevents detectable motion

Although humans are sensitive to acceleration, Earth's nearly circular orbit around the sun and its slow spin relative to its size produce negligibly small, minimally changing accelerations. However, the changing seasons and the day-night cycle are evidence of Earth's movement through space, as verified by satellites and telescopes.

What's the difference between an ale and a lager?

The major distinction is that ales are typically fruitier, while lagers are cleaner and crisper. This video breaks down several more of the nuanced differences between the two styles.

Sex determination isn't all XX and XY

We're generally taught that chromosomes determine an animal's sex, but it is way more nuanced than that. Watch this 12-minute video to find out how.

Lack of sunlight during Arctic winters can fuel a winter slump and a circadian disconnect.

One theory claims the retinae of SAD patients may fail to adjust to less light in winter

Most people’s eyes become more sensitive to light in the winter months, but some do not. This failure to adjust causes ripple effects on those individuals’ biological clocks. This Ted-ED video provides a clear, brief, narrative explanation of the condition in six minutes.

In 1676, Danish astronomer Ole Rømer determined that light did not travel instantaneously by observing a delay in the appearance of solar eclipses on Jupiter when it was farther from Earth.

Railroads and long-distance communication led to the development of time zones, with Greenwich established as the prime meridian—the longitude of 0 degrees—due to British advancements in star mapping and navigation.

The moon's gravity exerts an overall pressure that displaces the oceans toward the opposite sides of Earth's equator, producing tides.

Visualize the path of every solar eclipse from 1900 to 2099 and see what each looks like when observed from different locations on Earth.

Wind is the movement of air caused by the sun's uneven heating of Earth

The tilt, curvature, and variations in Earth's surface composition across the globe cause different regions to receive different amounts of solar radiation. As the Earth spins and tries to achieve thermal equilibrium, air masses move and interact, creating wind.

How jet streams and US weather are affected by the El Niño-Southern Oscillation

Jet streams are predominantly west-to-east air currents in the atmosphere that mark the boundary between cold polar air and warm tropical air, where cells of atmospheric circulation meet. By disrupting the location of these circulations on two- to seven-year cycles, ENSO alters the probability of droughts, floods, and above- or below-average temperatures across the US.

Learn all about different types of extreme weather

Find out in more detail about different types of extreme weather, from flooding to thunderstorms, from tropical cyclones to sandstorms, and more (w/ helpful videos).

What's the difference between an ocean, sea, and saltwater lake?

What are the seven seas, the five oceans, and why isn't the Dead Sea considered a sea? This overview provides definitions for each.

The faint triangle of light occasionally seen above the horizon, known as zodiacal light, is due to sunlight reflecting off ice and dust scattered throughout the inner solar system.

Take a virtual tour inside Stonehenge, the stone monument built roughly 5,000 years ago.

Prehistoric visitors approached Stonehenge along a processional route known as the Avenue, where the sunrise of the summer solstice aligns with the sarsen stones. This interactive 3D tour recreates that experience with explainer videos and detailed sidebars.

How the moon moves, an interactive lesson

How exactly does the moon move, and why does it move that way? In this ridiculously comprehensive interactive explainer, you can conduct experiments to see how the moon rotates and as it moves around the Earth, while learning how gravity works by controlling the path and speed of different objects. Dive into this beautiful, simple explainer to learn the basics on gravity and the moon.

Earth's oceans do mix, despite viral images and videos claiming to show boundaries between oceans that waters do not cross.

Day of the Dead differs from All Souls’ Day in several important ways

The holidays share a calendar date and both honor lost loved ones. However, All Souls’ Day is intended to help guide souls in purgatory to heaven, while Day of the Dead celebrates the temporary return of loved ones’ spirits to Earth.

How the moon creates tides

Anyone who has visited large bodies of water virtually anywhere on Earth notices low and high tides occur at regular intervals, a process primarily driven by the moon’s gravitational pull. This explainer details how the motion of the Earth and Moon interact to create tides.

Auroras take place all day long, but are too faint to see during the day

Because the sun constantly emits charged particles into the solar system, Earth's magnetic field deflects them continuously, with a small subset becoming trapped and colliding with atmospheric gases. Daylight, light pollution, and weather prevent the northern and southern lights from being seen most of the time, even for those at higher latitudes.