Hyades (star cluster)

A big group of stars lives near us.

They all stay together in a bunch. They move through space as one. This group looks like a V in the sky.

Some stars in the group are very big. These stars have used up their fuel. Now they are giant stars.

One star in the group has a planet. This was the first planet found in a group like this. The stars are also very old. They are 625 million years old.

Many stars stay in the middle. The middle is very crowded. Some stars drift far away. They leave the group.

This group helps us find the bull in the stars. It is a beautiful sight in the night sky.

The Hyades is a group of stars called an open cluster.

An open cluster is a bunch of stars that stay together. These stars share the same age and place of birth. They also move through space in the same way. This group is about 153 parsecs away from our Sun.

In the sky, the Hyades looks like a "V" shape. It sits in the constellation Taurus. One bright star, Aldebaran, looks like it is part of the group. However, Aldebaran is not a member. It is much closer to Earth. The Hyades stars are about 625 million years old. Some of the brightest stars are now giants. They became giants after they used up their hydrogen fuel. One star, Epsilon Tauri, even has a planet. This was the first planet found in an open cluster.

The cluster has a crowded middle called a core. Most of the heavy stars stay in this core. This is due to mass segregation. Mass segregation is a way that heavy stars stay in the center. Lighter stars often drift to the outer edges. These stars may eventually leave the group. This way of leaving is called evaporation.

The Hyades is a very special group of stars known as an open cluster.

It is the closest open cluster to our Sun. This group consists of hundreds of stars that share the same age and birthplace. They also move through space in the same direction. Because they are so close, scientists study them very carefully. This cluster is about 153 parsecs away from us. It is an important tool for measuring distances in the deep universe.

When we look up, the Hyades stars form a "V" shape in the constellation Taurus. One very bright star named Aldebaran sits right near this shape. Even though it looks like part of the group, Aldebaran is not a member. It is only 65 light-years away, while the Hyades is much further. The brightest stars in the cluster have changed over time. They used up the hydrogen fuel in their cores. This caused them to grow into huge stars called giants. One star, Epsilon Tauri, even has a candidate gas giant planet nearby. This was the first planet ever found in an open cluster.

People have known about the Hyades for thousands of years. In ancient Greek myths, the stars were the five daughters of Atlas. They were also the half-sisters of the Pleiades. In England, people once called them the "April Rainers" because of spring showers. Giovanni Battista Hodierna likely first catalogued them in 1654. Later, astronomers like Lewis Boss studied how these stars move together. He helped show that many scattered stars belong to the same moving group. This group is often called the Hyades Stream.

Scientists use amazing tools to learn about the cluster. They use the Hipparcos satellite and the Hubble Space Telescope to measure distance. They do this by watching how stars seem to shift as Earth orbits the Sun. This shift is called parallax. Other studies using the Gaia satellite have mapped thousands of members. These studies found 1,764 candidates, including white dwarfs and brown dwarfs. The cluster is about 625 million years old. It is also richer in heavy elements than our own Sun. This measurement is called metallicity, and the Hyades has a value of +0.14.

Inside the cluster, the stars are not spread out evenly. There is a crowded center called the core. Most of the heavy stars stay in this middle part. This happens because of a process called mass segregation. In this process, heavy stars sink toward the center. Lighter stars get pushed toward the outer edges, called the halo. Eventually, these light stars might drift away entirely. This way of leaving is called evaporation. It is how clusters slowly change and break apart over time.

The Hyades is the nearest open cluster to our Sun.

An open cluster is a group of stars that share the same age and birthplace. These stars also share the same chemical characteristics and motion through space. Because the Hyades is so close, it is one of the best-studied star clusters in the sky. It serves as a vital rung on the cosmic distance ladder. This means scientists use its known properties to help estimate distances to much further objects in the universe.

From Earth, the Hyades appears in the constellation Taurus. Its brightest stars form a distinct "V" shape. The star Aldebaran sits near this shape, but it is not a member of the cluster. Aldebaran is only 65 light-years away, while the Hyades is much further. The cluster center is approximately 153 parsecs from the Sun.

Scientists have measured this distance using parallax. Parallax is the apparent shift of a star as Earth orbits the Sun. This measurement was made with high accuracy by the Hipparcos satellite and the Hubble Space Telescope.

Another way to find the distance is by using a color–magnitude diagram. Astronomers look at the intrinsic brightness of stars and compare it to how bright they appear from Earth. This method also yields a distance of about 153 parsecs. The Hyades is also chemically unique. It has a metallicity of +0.14. Metallicity refers to the amount of elements heavier than hydrogen and helium. This means the Hyades stars are more enriched with heavy elements than our Sun.

The Hyades is about 625 million years old. Most stars in the cluster are still on the main sequence, which is the stage where they fuse hydrogen. However, the five brightest stars have already evolved into giant stars. These stars consumed the hydrogen fuel in their cores. This caused them to grow much larger. Four of these giants, along with Aldebaran, form an asterism known as the head of Taurus. One star, Epsilon Tauri, is even a candidate for hosting a gas giant exoplanet. This would be the first planet discovered in any open cluster.

Recent studies using the Gaia satellite have mapped the cluster in great detail. A 2019 study identified 1,764 member candidates. This list includes 10 brown dwarfs and 17 white dwarfs. White dwarfs are the dense remains of stars like our Sun. The cluster also shows a history of mass segregation. This is a process where heavier stars sink toward the center of the cluster. This creates a dense core with a radius of 2.7 parsecs. Lighter stars are pushed toward the outer edges, known as the halo.

Over time, the cluster undergoes a process called evaporation. In this process, smaller stars are scattered outward by the gravity of more massive stars. These stars move into the halo, which extends to the tidal radius of 16 parsecs. Beyond this limit, the gravity of the Milky Way galaxy begins to pull stars away. About one-third of the confirmed member stars are already in this halo. These stars are likely in the process of escaping the cluster entirely.

The Hyades has a long history in human culture. In Greek mythology, the Hyades were the five daughters of Atlas. They were also the half-sisters of the Pleiades. In England, they were called the "April Rainers" because they were associated with spring showers. Astronomers have studied them for centuries. Giovanni Battista Hodierna likely first cataloged them in 1654. In the 1900s, Lewis Boss studied the Hyades Stream. This is a collection of scattered stars that share a similar trajectory to the cluster. While many stars in the stream move similarly, about 85% are actually unrelated to the Hyades. Their motion is caused by the tidal effects of the Milky Way's central bar.