Pleiades

The Pleiades, also known as the Seven Sisters and Messier 45 (M45), is an asterism of an open star cluster with young B-type stars in the northwest of the constellation Taurus. It is about 444 light-years from Earth. The Pleiades is one of the nearest star clusters to our planet and the closest Messier object that can be seen with the naked eye in the night sky. This cluster has bright stars and beautiful reflection nebulae such as NGC 1432 and NGC 1435, also called the Merope Nebula.

The Pleiades is made up mostly of hot blue luminous stars that formed within the last 100 million years. These stars shine brightly and make a wonderful view in the night sky. Even where there are many city lights, called light pollution, the Pleiades can still be seen.

Scientists think the Pleiades started much closer together, similar to the Orion Nebula. Over time, the stars have moved a little apart, and they will keep moving apart. In about 250 million years, the Pleiades will no longer look like a cluster because the stars will be too far apart to seem close together in the sky.

Along with another famous group of stars called the Hyades, the Pleiades forms what is known as the Golden Gate of the Ecliptic. People often say the shape of the Pleiades looks like a tiny dipper, but it is not the same as the "Little Dipper" in the constellation Ursa Minor.

Origin of name

The name "Pleiades" comes from Ancient Greek. The cluster helped people know when it was safe to sail in the Mediterranean Sea. In Greek stories, the Pleiades were seven sisters. People later said they were the "daughters of Pleione," a mythical mother. The name started from how the stars helped with sailing.

Astronomical role of M45 in antiquity

The Pleiades, also called M45, was important to people long ago when they made calendars. Its special shape in the night sky near the ecliptic made it easy to spot. Around 2330 BC, this group of stars marked an important time of year.

The Pleiades appeared on old objects like the Nebra sky disc from about 1600 BC. Many ancient cultures, such as India, Mesopotamia, Greece, and Arabia, used the Pleiades to help start their calendars. Even as its place in the sky changed, it stayed important to people in many lands.

Nomenclature and mythology

The Pleiades have been known for thousands of years by many cultures around the world. People from places like Celts, Filipinos, Hawaiians, Māori, Indigenous Australians, Persians, Arabs, Chinese, Japanese, and many others have given the Pleiades special names and meanings. In Hinduism, they are called Kṛttikā and linked to stories about gods and goddesses.

The Pleiades appear in old writings and artworks, like the Nebra sky disk from around 1600 BC. Ancient Greeks wrote about them in poems, and they are mentioned in the Bible. In Japan, the cluster is known as Subaru, which means "to cluster together." This name is used for the Subaru Telescope in Hawaii and also appears in the logo of Subaru cars. In the stories of J. R. R. Tolkien, the Pleiades are called Remmirath, the netted stars.

Observational history

Galileo Galilei was the first astronomer to look at the Pleiades with a telescope. He found that the group has many stars too faint to see without a telescope and wrote about this in 1610.

People have always seen the Pleiades as a group of stars close to each other. By watching how the stars move in the sky, scientists learned they all move together, proving they are part of the same group. Charles Messier added the Pleiades as "M45" to his catalogue of special objects in 1771.

Distance

The distance to the Pleiades helps astronomers measure how far away things are in space. Because the Pleiades is close to Earth, scientists have tried many ways to find its exact distance. Different tools have given slightly different answers, but most recent measurements say it is about 135 parsecs away.

Knowing this distance helps astronomers learn how far other star clusters and galaxies are from us. The Pleiades is a key example for testing these distance-measuring tools.

Composition

The Pleiades cluster has many stars, more than 1,000 of them. Some are bright blue stars that you can see without a telescope. These stars look like shapes of the constellations Ursa Major and Ursa Minor.

The cluster also has brown dwarfs, like Teide 1. Brown dwarfs are smaller than stars and do not shine very brightly. They are easier to study when they are young, like the ones in the Pleiades.

Members

The brightest stars in the Pleiades cluster are named after the Seven Sisters from Greek mythology: Asterope, Merope, Electra, Maia, Taygeta, Celaeno, and Alcyone. These stars are linked to their parents, Pleione and Atlas. The ancient Greeks did not give these stars individual names. Later, astronomers gave them names. These names were first used in a book from 1665 and became official in the 19th century.

Age and future evolution

Scientists study how stars change over time to figure out how old star clusters are. The Pleiades is thought to be between 75 and 150 million years old. By studying small stars called brown dwarfs, which can hold onto a special material called lithium, scientists believe the Pleiades is about 115 million years old.

The Pleiades is moving toward the feet of the constellation Orion. Over time, the cluster will spread out because of gravity pulling its stars apart. It is expected to spread out in about 250 million years due to interactions with big clouds of gas and the spinning arms of our galaxy.

Reflection nebulosity

With bigger telescopes, you can see a soft glow around some stars in the Pleiades. This glow is called a reflection nebula. It happens when dust shines because of the blue light from hot, young stars.

Scientists once thought this dust was left over from when the cluster began. Now, they think the cluster is moving through a dusty part of space. The dust is not spread out evenly. It is mostly in two layers that we can see.

Possible planets

Astronomers used the Spitzer Space Telescope and Gemini North telescope. They found that a star in the Pleiades, called HD 23514, has lots of hot dust around it. This dust could be the start of planets forming.