Zodiacal light

A soft glow shines in the night sky.

This light comes from tiny bits of dust. The sun hits the dust. This makes the light shine. It can look like a fake dawn.

This dust is mostly from comets. Some dust may come from Mars, too. The dust stays in a big cloud. It spreads across the sky. You can see it best when the sky is dark.

It is a beautiful sight to see.

Have you ever seen a faint glow in the night sky?

This is called zodiacal light. It is a soft light from sunlight. The light hits tiny bits of dust in space. This dust is called interplanetary dust. The dust stays in a large, flat cloud. This cloud is shaped like a pancake. It spreads across the path of the planets. We call this path the ecliptic.

You can see this light best in a dark sky. Moonlight or city lights can hide it. Some people call it a "false dawn." This is because it can look like the sun is coming up.

Where does this dust come from? Most of it comes from comets. These are icy objects in space. When comets break apart, they leave dust behind. More than 85 percent of the dust is from comets. Some dust might also come from Mars.

Scientists use spacecraft to study this dust. They want to learn how the cloud stays so thick. New dust must arrive to replace the old dust.

Have you ever looked at a very dark night sky and seen a faint, ghostly glow?

This light is called zodiacal light. It is a soft glow caused by sunlight hitting tiny bits of dust in space. This dust lives in a huge, flat cloud called the interplanetary dust cloud. The cloud is shaped like a pancake and sits along the ecliptic. The ecliptic is the path that the planets follow around the Sun. Because the dust is spread out, it makes the whole sky look a little brighter.

This light works through a simple step-by-step process. First, sunlight travels through our solar system. Next, that light hits tiny grains of interplanetary dust. These grains are very small, ranging from 10 to 300 micrometres. The dust scatters the sunlight in different directions. This scattering creates the glow we see from Earth. The light is brightest when we look near the Sun. This happens because the dust particles closest to our line of sight scatter the most light. You might also see a small, bright oval called the gegenschein. This is a related glow that appears directly opposite the Sun.

People have wondered about this light for a very long time. Mesoamericans were aware of the zodiacal light before the year 1500. It was perhaps first written about in print by Joshua Childrey in 1661. Later, the astronomer Giovanni Domenico Cassini studied it in 1683. Some say Nicolas Fatio de Duillier was the first to explain the light using dust. In the 1970s, spacecraft like Pioneer 10 and Helios gave us even more clues. These missions proved that the light really does come from dust in our solar system. Even famous musicians have studied it! Brian May, the lead guitarist for Queen, finished his science thesis on this dust in 2007.

There are many interesting facts about this cosmic dust. More than 85 percent of the dust comes from Jupiter-family comets. These are comets that orbit the Sun in less than 20 years. Some dust also comes from collisions between asteroids. Data from the Juno mission in 2020 suggested some dust might come from Mars. This dust is so small that it can be as tiny as one nanogram. If the dust were larger, like 1 millimetre pieces, they would be 8 kilometres apart!

This shows how thin the dust cloud actually is.

You can think of zodiacal light as a natural way the sky stays bright. It is a part of the natural light of a clear, moonless night. In some cultures, it has a very special meaning. The prophet Muhammad described it as a "false dawn." This helped people tell the difference between the zodiacal light and the true dawn at sunrise. This was important for timing daily prayers and fasting. Just like the stars you know, this light tells a story about the tiny pieces of our solar system.

Zodiacal light is a faint, diffuse glow of sunlight scattered by interplanetary dust. This phenomenon appears as a soft light spread across the sky, contributing to the natural light of a clear, moonless night. It is often most visible as a triangular shape extending from the Sun's direction along the zodiac. Because the light is quite subtle, it is easily hidden by moonlight or light pollution.

When viewed in the evening, it can look like a false dawn, and it is also known by this name. This light provides a window into the composition of our solar system.

The mechanism behind this glow involves a specific sequence of physical events. First, sunlight travels through the solar system and encounters the interplanetary dust cloud. This cloud is a thick, pancake-shaped collection of particles that straddles the ecliptic plane, which is the path the planets follow. As the sunlight hits these grains, the light is scattered in different directions. The particles range in size from 10 to 300 micrometres, with masses between one nanogram and tens of micrograms. The light is brightest when observing at a small angle toward the Sun because of strong forward scattering.

There are distinct ways to observe this light depending on your position relative to the Sun. One specific feature is the gegenschein, or counterglow. This appears as a faint but slightly brighter oval glow located directly opposite the Sun. While the zodiacal light is most intense near the Sun, the gegenschein is caused by sunlight backscattered from the dust. Additionally, the dust band itself is uniform across the entire ecliptic. However, the dust further from the ecliptic is almost undetectable unless viewed at a small angle toward the Sun.

History shows that humans have observed this light for centuries. Mesoamericans were aware of the zodiacal light before 1500. It was likely first reported in print by Joshua Childrey in 1661. In 1683, the astronomer Giovanni Domenico Cassini investigated the phenomenon. Some records suggest Nicolas Fatio de Duillier was the first to explain the light using dust particles. In the 1970s, the Pioneer 10 and Helios spacecraft provided crucial observations. These missions confirmed that the light is indeed scattered by the interplanetary dust cloud.

The origin of this dust has been a subject of intense scientific debate. It was previously thought that the dust came from comet tails and asteroid collisions. We now know that over 85 percent of the dust comes from the fragmentation of Jupiter-family comets. These are comets with orbital periods of less than 20 years that are often nearly dormant. The Poynting-Robertson effect causes these dust particles to spiral slowly into the Sun. This means a continuous source of new particles is required to maintain the cloud.

Recent data has added new layers to our understanding of the dust's source. Analysis from the Juno spacecraft suggests that dust near Earth might have a local origin from Mars. This dust distribution extends from Earth's orbit to the 4:1 orbital resonance with Jupiter. However, researchers are still working to explain how this dust could escape Mars' gravity. Furthermore, the 2015 Rosetta mission confirmed that Jupiter-family comets, such as comet 67P/Churyumov–Gerasimenko, are likely the primary parent bodies. This dust is so sparse that if the particles were 1 mm in size, they would be 8 km apart.

Zodiacal light also has significant cultural and scientific connections. In Islam, the prophet Muhammad described the light as a "false dawn." This distinction helped practitioners differentiate it from the "true dawn" to time daily prayers and fasting correctly. In modern science, the study of this dust is vital for space exploration. Dust around other stars, called exozodiacal dust, can interfere with the imaging of distant planets. Interestingly, these hot debris disks can actually indicate the presence of planets, as planets tend to scatter comets into the inner solar system. ]