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.

How the pigments that absorb light for photosynthesis contribute to plants' green color

Although light energy is captured to power the reactions that produce the building blocks of starch, cellulose, glucose, and other sugars, chlorophyll a and b are most sensitive to violet, blue, orange, and red light, leaving green light mostly unabsorbed. This green light is instead reflected, giving most plants this color appearance.

Breaking down sunlight and why the sun appears yellow despite emitting green light the most

This peak intensity is produced alongside a spectrum of other colors, which, when combined, make the sun appear white in space. Since Earth's atmosphere scatters bluer and greener wavelengths of light more than red and orange wavelengths, sunlight reaching Earth's surface appears yellow, while the sky appears blue. (Some readers may experience a paywall.)

Solar activity and the density and chemical composition of the air affect auroral colors

Oxygen atoms can emit red and green light when energized by collisions with the solar wind, but red takes longer to be emitted and is disrupted by bumping into other molecules. This causes red light to appear at higher altitudes, where the air is less dense. Higher-energy solar wind can penetrate to lower altitudes and collide with more abundant ionized nitrogen, which produces blue light.

View a fall foliage prediction map to estimate the progressive change in the color of leaves throughout the US from September to mid-November.

Imagining if humans could perform photosynthesis and how it would change our anatomy

Since chloroplasts reflect green light, becoming photosynthetic would give our skin a green appearance. Because photosynthesis has efficiencies of only 5% to 9%, and humans burn 2,000 Calories daily compared to about 200 burned by a tree, becoming photosynthetic would also require us to adopt a less active, sun-filled lifestyle.

Many trees lose their leaves in the fall to conserve resources for future blooming rather than spending them on keeping leaves alive in the wind and cold of winter.

Red and green became Christmas colors thanks to holly—and Coca-Cola

Holly's green leaves and bright red berries linked the colors to winter festivals for centuries, but Coca-Cola's 1931 Santa—painted by Haddon Sundblom in Coke-red robes—helped cement red and green as the modern Christmas palette.

Why so many cartoons are yellow

"The Simpsons" creator Matt Groening said he found the skin tones of cartoon characters to be "freakish" and wanted his show to stand apart from everything else on television. His colorist proposed making them yellow, which color theory suggests would make the characters pop off the screen.

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.

An overview of oxygenic photosynthesis, which releases oxygen from breaking down water

Within the membranes of chloroplasts, electrons in pigments are energized by light and transferred across a series of molecules until they create the energetic NADPH molecule. This transfer also powers a hydrogen pump, which creates an ion imbalance that, when relieved, produces energetic ATP molecules. Outside the membranes, both NADPH and ATP are used to synthesize G3Ps, which are funneled into other metabolic pathways to produce sugars.

Without liver bile, human poop would be a pale silver color

Stomach acid and enzymes break down food into smaller particles, expelling a semi-fluid mass called chyme into the small intestine, where bile is added. As the intestines absorb nutrients and water, the chyme solidifies and changes color.

Stress-induced hormones contribute to gray hair

When the body experiences stress, the sympathetic nervous system releases the hormone norepinephrine. This hormone prematurely activates pigment-producing cells (melanocytes) in hair follicles, which depletes the hair's ability to retain color over the long run.

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.

From the surface, Mars can appear butterscotch, golden brown, and even green

Images from orbiters, landers, and rovers show that Mars has a mix of surface colors resulting from variations in the mineral compositions of different regions. The reddish tint when viewed from Earth comes from kicked up particles of rusted iron.

The extremophilic origins of watermelon snow and its impact on glacial melting

Also known as "blood snow," the red coloration is produced by snow algae that thrive in extremely cold conditions and take the shape of red spherical cysts in winter. To protect themselves from more intense summer solar radiation, these psychrophiles accumulate red, orange, and yellow pigments, intensifying their coloration and causing glaciers to reflect less sunlight than if they were white.

Watch a time-lapse from space of photosynthesis across Earth

Using NASA satellite imagery, carbon absorption can be tracked and serves as a proxy for photosynthetic activity on land and in the oceans. Over the course of a year, seasonal changes can be observed as plants become dormant in the fall and active again in the spring.

Climate change is disrupting maple syrup by shortening its production season

The number of unusually warm winter days in parts of Maine has increased significantly over the past few decades, stressing maple trees into shifted sap flows and leaving producers with less consistent outputs.

Water is naturally tinted with a slight blue, but sediments and organics can alter its color

The innate coloration comes from water absorbing red light in the visible spectrum more than green or blue, giving shallow waters in some parts of the Caribbean their turquoise hue. If sand is light, it can be churned up by turbulent water, clouding its appearance. Plankton and other organisms can color water by affecting how the rest of the spectrum is absorbed or reflected.

What is the rarest color in nature?

Plants, animals, or minerals found in nature bear almost every color imaginable. There are two factors that influence what hues you see in the wild: physics and evolution. So, which colors are you least likely to see in the natural world? Victoria Hwang explores one of nature’s rarest spectacles.

LEDs emit pure colors, while incandescent bulbs filter white light

Traditional Christmas lights produce softer, less saturated colors by partially blocking the full spectrum of light, resulting in a particularly warm glow by dimming the cooler blue tones. LEDs are designed to emit a single wavelength of light, creating intense colors that are visually unbalanced in multicolor environments.

Visualize the purpose of stomata in photosynthesis

These openings on the underside of leaves can be opened and closed by specialized guard cells to regulate the movement of carbon dioxide into and oxygen out of cells, thus impacting the rate of photosynthesis. At night, when the light-dependent reactions in photosynthesis are not possible, the stomata close to prevent the plant from losing water through transpiration.

A diamond's color comes from impurities, defects, and unique formation processes

While most diamonds are transparent and sparkly, the presence of nitrogen and boron during formation can make them yellow, orange, or blue. Radiation can produce green diamonds, and structural deformities can introduce red hues.

How house colors can indicate gentrification

Reporters from the Washington Post share an analysis that indicates gray and neutrally toned houses are signs of gentrification in a neighborhood. Visuals of different paint swatches help illustrate which colors are chosen for newly built homes in certain DC districts.

Red blood, skin, hair, and nail cells destroy their DNA upon maturing

To maximize the amount of oxygen they carry and more easily alter their shape to fit into narrow blood capillaries, red blood cells destroy their own nuclei. Cornified cells found in hair, nails, and the outermost layer of skin destroy their nuclei and other cellular contents to make room for keratin, which provides durability and structural support.

Copper is responsible for turning blonde hair green in swimming pools

Pools use copper sulfate to control algae, which can bind to hair either damaged by the sun or recently bleached. Chlorine, which is often considered to be the culprit, weakens the hair structure to exacerbate the green coloration reaction, rather than causing it.

During coral bleaching, corals sacrifice their food source and expel colorful microorganisms to protect themselves, a phenomenon that resembles an organism's immune system attacking itself.

Watermelons were once neither red nor sweet

The gargantuan summer picnic staple has a fascinating story: 100 million tons are produced worldwide and they take up the most space of any vegetable crop in the world. But not long ago, the flesh of the melon was white and it had a bitter taste.

Melanin and light scattering contribute to different eye colors

Brown eyes have high melanin, while blue eyes have low melanin. Multiple genes contribute to eye color, which can change over time due to melanin buildup. Hazel eyes can shift color depending on ambient light.

Red is deeply symbolic in Chinese culture

Since the bold hue warded off the mythical Nian, the color red has come to represent luck, prosperity, and celebration. If you come across a home or neighborhood preparing for new year celebrations, you'll see red lanterns, wall hangings, clothing, and more.

Watch underwater photosynthesis make water look like champagne

In shallow waters where sunlight can reach, photosynthetic reactions absorb water and dissolved carbon dioxide, producing bubbles of oxygen at the surface of plants. As these bubbles rise to the water's surface, a fizzy appearance is created.

An explanation of the Calvin cycle, including why it needs to run six times to create glucose

Each run of this second phase of photosynthesis begins with a five-carbon molecule called RuBP, which gains an additional carbon atom when carbon dioxide (CO₂) is attached. Across six cycles, the six six-carbon molecules—36 carbon atoms in total—are processed into 12 three-carbon sugars, which can be used to generate glucose, and six RuBP molecules, enough for each cycle to restart.

Discover the chemistry behind smoking foods, including the types of smoking and the source of smoking flavors and colors.

Eggshell color doesn't indicate taste or superiority

Brown, white, and blue eggs taste and cook identically. Despite popular notions that brown eggs are superior, the shell color reflects the genetics of the hen alone. What actually determines egg quality is freshness and the diet of the hen (where grass and leafy greens lead to denser yolks). And freshness can go both ways: older eggs peel more easily than fresh ones.

'Some painters transform the sun into a yellow spot, others transform a yellow spot into the sun.'

- Legendary artist Picasso (1881–1973)

Pill bottles have often been orange to help protect medication from UV light

Amber pill bottles were introduced in 1968 to keep medications potent while allowing patients to see how much medication they had left. The color has since become universally associated with prescription medication.

Red and blue election maps are a modern media invention

The red–blue color scheme used on election night maps emerged in the 20th century as television networks adopted color graphics to make results easier to follow. The association of red with Republicans and blue with Democrats later became standardized.

Bioluminescence produces new light while biofluorescence re-emits absorbed light

A chemical reaction between luciferin and oxygen—catalyzed by luciferase—produces light within bioluminescent organisms. Biofluorescence, on the other hand, involves special proteins that absorb light of one wavelength and re-emit the light at a different, typically longer, wavelength.

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...

See how fireworks are made and which metals are responsible for different colors

This roughly five-minute video breaks down details about how pyrotechnicians make fireworks, including that magnesium is responsible for white fireworks, copper salts for blue, and charcoal for orange.

Pigments in paint can come from rocks, plants, insects or synthetic sources

Paint's composition is varied through the combination of pigments with binding agents. In the past, artists created their own paints by mixing pigments with water, oils or egg yolks to bind the colors together.

How our sense of taste evolves as we age

Kids are hardwired to prefer sweets over greens, with sweetness a shorthand for calorie-rich and bitter flavor warning of potentially noxious plants. This holds true even in the womb, where fetuses have been seen via ultrasound scans grimacing as their hosts consume kale capsules. As they age into double digits and beyond, their taste cells and sense of smell diminish, leading to broader and less sensitive palates.

Poison ivy's rash-causing compound is found in the plant's roots, stem, and leaves—so coming into contact with any part of the plant can lead to rashes for the 85% of people who are allergic to it.

What is orange wine?

You've heard of rosé, a so-called anomalous wine. But what about orange wine? Orange wine is made using white wine grapes and red wine production methods. This guide walks you through the history of these wines—now trendy in the global market after being produced for thousands of years in places like Georgia. It also explores the flavors typically found in orange wine and how to pair it with food.

Seasonal allergies don't always show up in childhood

The human immune system may become sensitized to pollen and develop an allergic reaction to it after prolonged exposure. Other triggers for new seasonal allergies may include exposure to new environments and changing climate conditions that affect allergy season length and conditions for various pollens.

Marigolds are an iconic symbol of Day of the Dead

The native Mexican flower performs several functions in Day of the Dead celebrations. Its vibrance and unique scent help guide wandering souls home, and its cheerful color reminds celebrants that death can still be joyful.

Watch students comically portray how plants can detoxify the environment

Through a series of processes that collectively make up phytoremediation, plants can take up pollutants from soil and water through their roots, then break them down, release them as less harmful gases, or store them within their cells. Any plants that sequester heavy metals or other toxins must be removed and managed after the environment is decontaminated.

The fall is the best time of year to buy a car

The months of October through December are generally considered the best time to buy a car because old inventory is getting pushed out the door to make room for new cars. In addition to those months, some days of the week are considered better for car buying than others. To find out more, read this article.

Power lines are dotted with large, brightly colored balls to improve the visibility of these thin wires to helicopters and small planes and help prevent potential crashes.

Synchrotron radiation has revealed the fur color of creatures millions of years old

When electrons are accelerated in the loop, they produce intense X-rays that can reveal properties of a sample struck by them, just as X-rays can be used to show bone structure in humans. Studying the reflected light from fossils can uncover the presence of known pigmentation compounds.

Modern media exposure may impact whether people dream in color or black and white.