Halo (optical phenomenon)

You can see rings in the sky.

These are called halos. They come from tiny bits of ice. This ice floats in high clouds.

The light hits the ice. It bends and reflects. This makes bright circles or arcs. Some halos look like tall pillars of light. They can even show many colors. A halo might mean rain is coming soon. It is a beautiful thing to see.

Have you ever seen a bright ring around the Sun or Moon?

These are called halos. They happen when light hits tiny ice crystals in the sky. These crystals usually float in high clouds.

Sometimes, they float near the ground in cold weather. People call this diamond dust.

There are many kinds of halos. One common type is the 22° halo. It looks like a large ring. It is about the width of your hand held at arm's length.

This halo forms because ice crystals float in many different ways. This is different from other halos. For example, light pillars look like tall columns of light.

These pillars happen when crystals float flat, like tiny plates.

Halos can also look like colorful arcs. Some people use halos to guess the weather. A halo can mean rain might fall within 24 hours. This is because the clouds that make them can signal a change in the weather.

Have you ever looked up and seen a bright ring around the Sun or Moon?

These beautiful displays are called halos. They happen when light from the Sun or Moon hits tiny ice crystals in the sky. These crystals usually float in high clouds called cirrus or cirrostratus clouds.

In very cold weather, these crystals can even float near the ground. When this happens, people call the ice crystals diamond dust. Halos can take many forms, like white rings, colorful arcs, or bright spots.

How these shapes form depends on how the ice crystals move. The crystals act like tiny prisms and mirrors. As light passes through them, it is bent or reflected. This bending is called refraction. Some light is also split into different colors, which is called dispersion.

For a 22° halo, the crystals float in many different directions. This creates a large ring around the light source. Other shapes, like light pillars, need crystals to float flat like tiny plates.

These pillars look like tall columns of light rising from the Sun or Moon.

People have studied these lights for a very long time. Ancient thinkers like Aristotle mentioned them. In China, observers recorded many types of halos centuries ago. The "Official History of the Chin Dynasty" from the year 637 mentions them. In Europe, scientists like Christoph Scheiner and Johannes Hevelius wrote about them later.

A famous painting from 1535 shows a halo over Stockholm. This painting is called the "Sun Dog Painting." It shows white circles and arcs in the sky.

There are many specific facts about these light shows. The most famous is the 22° halo. It has a radius of about 22 degrees. You can see this size by holding your hand out at arm's length.

Another rare type is called Bottlinger's ring. It is an oval shape instead of a circle. Light pillars can appear when the Sun is within 6 degrees of the horizon. These pillars can also form around street lights or the Moon.

Halos are a great way to learn about the world around us. Long ago, people used them to guess the weather. Seeing a halo might mean rain will fall within 24 hours. This is because the clouds that make halos often signal a change in weather.

Today, scientists use computers and machines to study them. They even use water glasses to mimic how light bends through ice. It is amazing how much we can learn just by looking at the sky.

A halo is an optical phenomenon caused by light interacting with ice crystals in the atmosphere. This light typically comes from the Sun or the Moon. These displays can appear as white or colored rings, arcs, or spots. They often appear near the Sun or Moon, but some occur elsewhere in the sky.

Most halos form when ice crystals are suspended in cirrus or cirrostratus clouds. These clouds exist in the upper troposphere. In very cold weather, these crystals can also float near the ground. When this happens, the crystals are referred to as diamond dust.

The specific shape of a halo depends on the orientation and shape of the ice crystals. The crystals act like prisms and mirrors. As light enters a crystal, it undergoes refraction, which means the light bends. Light may also undergo reflection, where it bounces off the crystal faces. Because of dispersion, the light can split into different colors.

The crystals send shafts of light in specific directions based on these processes. This creates the various patterns we see from the ground.

There are many distinct types of halos. The most well-known is the 22° halo, which is a circular ring. It has a radius of about 22 degrees. You can estimate this size by holding an outstretched hand at arm's length. In a 22° halo, the ice crystals are oriented semi-randomly. This randomness causes no light to reflect toward the inside of the ring. Consequently, the sky inside the ring looks darker, creating a "hole in the sky" effect. Other types include light pillars and sun dogs. Light pillars appear as vertical columns of light. They are caused by hexagonal plate-shaped or column-shaped crystals. These crystals tend to orient themselves horizontally as they fall. Sun dogs are another common type of halo display.

Some halos are much rarer than others. A Bottlinger's ring is a rare, elliptical halo. It is shaped like an oval rather than a circle. It is difficult to see in the Sun's glare and is often seen around a dimmer subsun. Scientists suggest these are formed by very flat pyramidal ice crystals. These crystals must be suspended horizontally at uncommonly low angles.

Other complex displays include the circumzenithal arc and the Parry arc. These can appear as full halos or incomplete arcs in the sky.

Humans have observed and recorded halos for centuries. Aristotle mentioned halos and parhelia in antiquity. Chinese observers recorded these phenomena for a long time. The "Official History of the Chin Dynasty" from 637 recorded the "Ten Haloes." This text provided technical terms for 26 different solar halo phenomena. In Europe, Christoph Scheiner and Johannes Hevelius provided early descriptions.

A famous Swedish painting from 1535, the "Sun Dog Painting," depicts a halo display over Stockholm. This painting shows white circles and arcs and a pair of sun dogs.

Halos have significant practical and cultural meanings. Before modern meteorology, halos were part of weather lore. They were used as an empirical way to forecast the weather. Because cirrostratus clouds often signal an approaching frontal system, a halo can indicate rain within 24 hours. In some cultures, they are seen as omens. In the Cornish dialect, a halo is called a "cock's eye" and is an omen of bad weather. In Nepal, the sun halo is called "Indrasabha," relating to the assembly court of the god Indra.

Today, scientists use various methods to study or recreate these effects. They use computer simulations and experimental machines. One method involves rotating a single crystal around one or two axes. To create complex displays like the Lowitz arcs, researchers use engineered halo machines.

Scientists even use chemical approaches to precipitate salt solutions that form crystals. This allows them to study how different crystal geometries produce specific rings or arcs. These studies help us understand the physics of light and the atmosphere.