Red

Red is a bright color.

You can see it in a sunset. This happens because the air scatters blue light away. This leaves the red light to reach your eyes.

Many flags use red. Some people think red means danger. Others think it means love or joy. In some lands, red means good luck. It is even the color of the Red Planet, Mars. Red is a very special color.

Red is a bright color. It is part of the light we see.

Red light has a long wavelength. This means it travels in long waves.

Sometimes you see red in the sky. This happens during a sunset. The air scatters blue and green light away. This leaves the red light to reach your eyes.

Many countries use red on their flags.

Red can mean many things. Some people think it means danger. Others think it means love or joy. In China, red means good luck.

Animals see red in different ways. Many animals have dichromacy. This means they cannot see red well. For example, bulls cannot see red. They charge a cape because it moves.

In space, Mars is called the Red Planet. It looks red because of iron oxide on its surface. There are also red stars. These are called red giants. They are very large and bright.

Bulls react to motion, not the color red.

Red is a bright color found at the long end of the visible spectrum of light. It sits next to orange and is opposite to violet. This color has a dominant wavelength between 625 and 750 nanometers.

Scientists use different models to explain how red works. In the RGB model, red is a primary color used for screens. In the CMYK model, it is a secondary color made from magenta and yellow. Red can look many ways, from bright scarlet to dark burgundy.

Our eyes see red through a specific way of working. The human eye uses special cells in the retina called cones. Red is seen when the long-wavelength cones are stimulated.

Some animals see the world differently than we do. Many mammals, like dogs and cattle, have dichromacy. This means they can see blue and yellow but not red or green. Bulls do not actually see the red in a matador's cape. They charge because the cape is moving, not because of the color.

People have used red for a very long time. Prehistoric artists used red pigment made from ochre.

Ancient Egyptians and Mayans used red for ceremonies. Roman generals even colored their bodies red to celebrate wins. During the Renaissance, wealthy people wore red clothes dyed with cochineal. This dye came from crushing tiny insects. In the 19th century, people began making the first synthetic red dyes. These new dyes replaced the older, traditional ways of coloring cloth.

Red also shows up in the sky and in space. Sunsets often look red because of Rayleigh scattering. This is a thing that happens when sunlight travels through the air. Air molecules scatter blue and green light away from your eyes. This leaves the longer red waves to reach you.

In space, Mars is known as the Red Planet. It looks red because of iron oxide on its surface. There are also red stars called red giants. These stars are much larger and brighter than our Sun.

We see red in many everyday things too. Red pigments called anthocyanins make leaves turn bright in the autumn. These colors appear when sugar breaks down in the leaf. Red is also used in food coloring. One common type is Allura Red AC, which is often made from petroleum.

People use red to show many feelings. In the United States, it can mean heat or passion. In China and India, it is a symbol of happiness and good fortune.

Red is a color found at the long wavelength end of the visible spectrum. It sits next to orange and is opposite to violet. The dominant wavelength for red is approximately 625 to 750 nanometers.

In the RGB color model, red is a primary color. In the CMYK color model, red is a secondary color created by mixing magenta and yellow. It is also the complementary color of cyan. Reds vary greatly in shade and hue. They range from bright, yellow-tinged scarlet and vermillion to bluish-red crimson. They also vary from pale pink to dark burgundy.

Human vision of red involves specific cells in the retina called cones. The eye sees red when light stimulates the L (long-wavelength) cone cells. This occurs without stimulating the S (short) or M (medium) cone cells. Light just beyond this range is called infrared. Humans cannot see infrared, but we can sense it as heat. Many mammals, such as dogs and cattle, possess dichromacy. This means they can see blues and yellows but cannot distinguish red from green. Bulls are a famous example of this. They do not charge a matador's cape because of the red color. Instead, they react to the motion of the fabric.

Humanity has used red for thousands of years. Prehistoric artists used red pigment made from ochre. Ancient Egyptians and Mayans used red for ceremonies. Roman generals colored their bodies red to celebrate victories. During the Renaissance, the wealthy wore red costumes dyed with kermes and cochineal. Cochineal is a dye made by crushing tiny female insects from Mexico and Central America. In the 19th century, the first synthetic red dyes were introduced. These new dyes eventually replaced traditional pigments. Red has also carried heavy political symbolism. It was the color of communism and socialism. The Soviet Union used a red flag following the 1917 Bolshevik Revolution. China and North Vietnam also adopted red flags after their respective revolutions.

Red also appears in the sky through a process called Rayleigh scattering. This happens during sunrises and sunsets. As white sunlight travels through the atmosphere, air molecules and particles scatter the light. Shorter wavelengths, like blue and green, scatter more strongly. These colors are removed from the beam of light. At sunset, the path through the atmosphere is longest. This removes the blue and green components almost completely. Only the longer orange and red wavelengths reach the eye.

In astronomy, red is a vital indicator of physical properties. Mars is called the Red Planet due to iron oxide on its surface. Stars also show red characteristics. Red giants are stars that have exhausted their core hydrogen. They switch to thermonuclear fusion in a shell surrounding the core. These stars can have radii hundreds of times larger than the Sun. Red supergiants, like Betelgeuse, are even larger. They can have radii 200 to 1700 times greater than the Sun. Red dwarfs are another type of star. They are small, cool, and very common in our galaxy.

Technology also relies on the specific properties of red light. The ruby laser was invented in 1960. In 1962, the red helium-neon laser was developed. These were used in holography and education. Modern DVD players use red laser diode technology at 660 nm. Red lasers were also used in early compact disc technology. However, they are being replaced by blue lasers. This is because red's longer wavelength requires more space on a disc.

Nature produces red through various chemical processes. In autumn, leaves turn red due to pigments called anthocyanins. These are not present during the whole growing season. They develop in late summer as phosphate moves out of the leaf. This change in chemistry causes sugars to break down into anthocyanins. Bright light and cool nights help create brilliant colors. Anthocyanins also color fruits like cherries, raspberries, and apples. In food, synthetic dyes like Allura Red AC are common. This dye is often made from petroleum. Some countries in Europe do not recommend it for children. Because of health concerns, some companies use natural carmine instead.