As sunlight passes through our atmosphere, its energy becomes scattered in various directions. Shorter wavelength light waves such as blue tend to disperse more widely than their red counterparts.
John Tyndall and later Lord Rayleigh helped reveal why the sky appears blue.
What is the colour of the sky?
Rayleigh scattering is responsible for creating the blue hue in our sky. This occurs when sunlight passes through Earth’s atmosphere and is scattered by air molecules; shorter wavelengths (such as blue) tend to be scattered more than longer ones like red, which causes sunlight reaching Earth’s surface mostly to be blue in hue.
The color of the sky varies with the amount of dust or water droplets present in the atmosphere, which determines its intensity. When there are large quantities of aerosols or dust in the air, its darkness becomes evident while with less aerosols present, its brightness can become more prominent.
Many people believe that the ocean’s color reflects that of the sky; this is incorrect; rather, its hue comes from absorbing its hues. When the sun sits low on the horizon and needs to pass through more atmosphere layers before reaching its destination (i.e. visible light), more ultraviolet and infrared radiation from sunlight is absorbed; consequently tinting its visible beams with blue.
Why the sky is blue remains an enigma that wasn’t fully resolved until the 19th century. John Tyndall took an important first step toward unraveling its hue in 1859 by noting that sunlight contains all possible wavelengths; yet he could not explain why sunlight appeared blue to him.
Scientists only realized the color of the sky after it took some more years for them to understand that its hue was caused by atmospheric particles – specifically small droplets of water vapour and air – scattering light more effectively when combined. When water vapour mixed with dust forms an atmosphere where light scattering becomes even greater – which explains why skies often appear very dark during rain.
Sky blue is an extremely delicate and tranquil color, often associated with daydreaming and Alice in Wonderland or Pisces (the sign associated with dreamy waters). Additionally, it evokes images of tranquil sea waters.
Why is the sky blue?
One of the first questions a child will probably pose about nature is why the sky is blue. While there may be various answers available, such as sunlight reflecting off ocean waves or oxygen being a blue-colored gas, one correct explanation lies within sunlight itself: when passing through Earth’s atmosphere, light waves are scattered by molecules into all directions more frequently if their wavelengths include shorter waves like blue and violet wavelengths; thus producing bluer light at our zenith while those reaching us nearer the horizon are redder.
Noting the colors present in white direct sunlight is key to understanding why grass appears green, flowers red and wood brown; when looking at natural scenes illuminated with this hued light they should appear to contain all their original hues.
As Sun rays pass through our atmosphere, they encounter various particles such as dust and water droplets that are much larger than light waves themselves and therefore reflect it back as Rayleigh scattering. Light waves with longer wavelengths like red, orange and yellow wavelengths tend not to be strongly reflected by atmospheric particles; on the contrary, blue and violet wavelengths tend to be strongly reflected, giving our sky its distinctive blue hue.
Blue and violet light tends to be less absorbed than other wavelengths, meaning its energy can be spread more evenly across its full range. As such, these hues tend to be more noticeable.
Polarized blue and violet light waves are more likely to be scattered by molecules in the atmosphere, giving the sky its characteristic hue. Furthermore, this effect gives the Moon its characteristic blue color when near Earth.
What causes the sky to be blue?
As sunlight travels from the Sun through Earth’s atmosphere, its light is scattered by nitrogen and oxygen molecules in its path, with bluer wavelengths getting scattered more than red ones and creating what we perceive to be its color – giving our skies its blue hues.
Scientists still are unsure exactly why molecules scatter blue light more than any other colors, but one thing is clear – smaller particles tend to scatter it more readily than their larger counterparts and oxygen and nitrogen molecules found in our atmosphere are particularly small.
Another factor is our eyes’ greater sensitivity to blue wavelengths, and our brain’s interpretation of this scattered light as the color of the sky. So it follows that blue sunlight passes through our atmosphere more efficiently, giving an appearance of blue skies.
However, this does not explain the color of the sky at night or when the Sun is low in the sky; that color depends on other factors like humidity and dust in the air; countries nearer the equator tend to have more moisture and particulate matter in their atmosphere than Australia, leading to bluer skies than Australian cities. When there’s been lots of dust or fire-generated by recent volcanic eruptions for example, redder skies can occur quickly.
Astronomers have examined the color of the sky from space. Their observations show that skies on other planets tend to resemble ours with certain differences; Mars for instance has an extremely red sky due to a dearth of water in its atmosphere and extreme dustiness; Venus by comparison has a blue hue due to having much denser atmospheres than our own, scattering less light, being extremely hot, and having yellow tinted air due to low density compared to Earth; Rayleigh scattering plays a part as does changes in humidity and dust levels in its atmosphere compared with changes here on Earth; all this adds up to explain why our skies look blue: the presence of water/gases/dust combinations all play their part resulting in this effect; all this together helps form this planet’s unique blue hue!
What causes the sky to be red?
As light travels through the atmosphere it is scattered by tiny molecules of nitrogen and oxygen – this phenomenon is known as Rayleigh scattering – with shorter wavelengths of visible spectrum colors (violet and blue) being most affected; hence why sky appears blue during daylight hours.
As the sun descends low into the sky at sunrise or sunset, its light must travel further through the atmosphere. This disperses more diffusely so that longer wavelengths such as red can make their way to our eyes; giving a brilliant hue to the sky during these times.
Scientists hypothesize that the current hue of the sky may be caused by dust particles suspended in the air. Similar effects cause white-looking skies near mountains or volcanic eruptions. Smaller particles scatter all wavelengths of visible light but are most effective at scattering blue than violet light wavelengths.
Red skies can often be found during sunset when forest fires or volcanic eruptions are nearby, or after volcanic activity has taken place. But even on a clear day the sky can appear red if pollution levels in the air reduce Rayleigh scattering sufficiently, allowing shorter wavelengths like red and green wavelengths that stimulate our eye’s red and green cones more readily to pass through our atmosphere.
These colors are also the ones most affected by dust or smoke in the air, since their wavelengths tend to be scattered more easily and therefore less likely to reach our eyes. When there’s lots of pollution in the air, red skies appear. Cities tend to experience this more than rural areas do due to greater pollution levels. Red skies can also appear during tropical storms or large dust storms and Leonardo da Vinci wrote extensively about this phenomenon in his notebooks while watching sunlight pass through wood smoke.