Five things to know about autumnal equinoxes

The difference between solstice and equinox, explained

A solstice marks the extremes in the amount of day or night, while the equinoxes come on days with a balance between the two. Learn why with this brief video.

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.

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.

The science of springtime, 101

Dive into the basics on springtime including the astronomy that brings it about, natural signs of spring's arrival, and some of the cultural approaches to the season.

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

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.

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.

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.

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.

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.

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.

Emulating Earth’s light-dark cycle is important for astronaut health and safety

Astronauts aboard the International Space Station experience 16 daily sunrises, but scientists have learned to try to promote circadian rhythms by phasing through several light settings aboard the ISS to improve astronauts’ sleep and productivity.

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

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.

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

Twelve ways the world celebrates springtime

Celebrating the seasonal change is rarely filled with as much relief and hope around the world as spring. This list compiles some famous and lesser-known springtime traditions from diverse cultures.

During the fall, shorter days trigger cells in leaves to produce less chlorophyll, a green pigment that is typically present in sufficient concentrations to mask other pigments, such as yellow and orange.

There is a template for how to live a better, healthier day, and it includes a digital sunset

Science suggests that early-morning exercise, later-morning peak work or social time, consistent exercise, and a "digital sunset"—starting to turn down the lights in the evening and avoid screens—are important for circadian health.

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.

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).

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.

Asia's agriculture-focused set of 24 'small seasons'

In contrast to the four broad seasons and their basis in astronomy and climate, ancient farmers in China and Japan had many more and varied seasons (or "sekki). Take Keichitsu (March 6 to 21), for example: this means "going-out of the worms" when bugs come out from hibernation.

The moon is moving 3.8 centimeters farther away from Earth each year

Driven by tidal forces, the effect is minimal and slow, ensuring stable tidal patterns and lunar cycles. Earth's rotation slows down as the Moon gains orbital momentum, slowly lengthening the day over time.

The side effects of falling back and springing forward

Daylight saving time can interfere with a person’s sleep schedule, but it also has been linked to increased rates of depression, heart attack, stroke, cancer, and car accidents. UT Southwestern’s Dr. Joseph Takahashi explains why the time change is bad for your brain and health.

Life during three months of polar night

In Norway's Svalbard archipelago, night reigns from November to January, as with many communities living within the polar regions. Contrary to popular assumptions about such places, many residents of the region describe the long darkness as peaceful, a time to slow down and draw nearer to neighbors and community. Read more on life in polar night, specifically in the Svalbard town of Longyearbyen, in this essay from a resident there.

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.

The solstice has been celebrated globally for millennia.

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.

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

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).

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.

Daylight Saving Time is linked to a rise in heart attacks and strokes

Losing an hour of sleep with seasonal time changes is not good for our health and it’s linked to risks for the first couple days of Daylight Saving Time, including a short-term rise in heart attacks and strokes. Scientists theorize these elevated risks are linked to the disruption to the body’s circadian rhythm.

Learn about various ocean-atmosphere cycles impacting global weather patterns

Although the El Niño-Southern Oscillation is among the most impactful, the North Atlantic Oscillation strongly influences weather patterns in the Northeast US by periodically changing atmospheric pressure over the Atlantic. The North Pacific Oscillation fluctuates atmospheric pressure and sea-surface temperatures that affect winter temperatures over much of the US.

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.

SAD disrupts melatonin secretion, producing it longer in the morning

The hormone is secreted from the pineal gland in the brain and is key to the timing of sleep. However, the substance does not generate sleep itself. With seasonal affective disorder, the body misperceives the photoperiod—the time with light—and the cycle of sleeping and waking gets off-phase, leading to issues with circadian rhythms.

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.

Circadian rhythms shift as we age—making older adults want to go to bed earlier

Throughout our lives our internal biological clocks shift. Early-to-rise toddlers become hard-to-wake teens and eventually early-to-sleep seniors. Circadian rhythm fluctuations throughout our life cycle explain some of these changes.

Ending daylight saving time may prevent as many as 300,000 strokes annually

Changing clocks twice a year disrupts circadian rhythms, which last an average of 24 hours and 12 minutes. Studies have shown that permanent daylight saving time provides fewer health benefits than standard time.

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...

New Year's Eve celebrations date back to ancient Babylon

Rather than celebrating in winter, the Babylonians honored the vernal equinox, a day in late March with equal amounts of darkness and light that signaled the start of a new year. They celebrated with Akitu, an 11-day festival.

From seed to pumpkin, a 3-minute time-lapse

Pumpkins are atypically enormous winter squashes, meaning they are harvested in the fall and then remain edible throughout winter. See how it all happens with this mesmerizing, music-backed time-lapse showcasing a pumpkin's 120-day journey from...

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.

If the sun disappeared, we would not know about it for 8 minutes and 20 seconds, at which point the Earth would suddenly move in a straight line on its way out of the solar system.

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.

The science of spring fever

Researchers have confirmed what people have sensed for ages: Our emotions during the springtime can go a little wild. This piece breaks down the impact of the seasonal transition on our bodies and prescribes a few ways to mitigate the effects.

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.

10 percent of SAD cases occur in the summer

Despite its significantly lower incidence, summer-risk SAD is as significant as its winter counterpart. Rather than being prompted by less light, the summer version is typically spurred by high temperatures, strong light, distinct summer time social pressures (appearing in a bathing suit, for example), and pollen. Common treatments include keeping cool and prioritizing sleep.

Blood moons only occur during total lunar eclipses, when the Earth blocks the sun, but its atmosphere lets redder parts of sunlight through to reflect off the lunar surface.

The hour originated from an ancient Egyptian astronomical system

The movements of astronomical objects, measured in a day and a year, form the foundation of our sense of time. The Egyptians divided each day and night into 12 time eras, using arbitrarily selected stars as references rather than movements of specific celestial objects.

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.