Messier 7

Many stars live close together.

They look like a big group. You can see them in the sky. They are near a shape called Scorpius.

People saw these stars long ago. One man saw them in the year 130. In China, they called them the fish.

A big tool can see more stars. It can see about 80 stars at once. This group is very old.

It is about 200 million years old. The stars are far away. They are made of the same stuff as our Sun.

It is a bright and pretty sight.

Messier 7 is a group of stars. We call this an open cluster.

It sits in a shape called Scorpius. You can see it with your own eyes. Long ago, a man named Ptolemy saw it. He lived in the year 130. In China, people called it Yú. This means "the Fish."

Many stars live in this group. Telescopes show about 80 stars at once. The cluster is very big. It is 25 light years across. A light year is how far light travels in one year. The stars are 980 light years away.

This cluster is about 200 million years old. The stars are made of similar stuff to our Sun.

In 2006, a spacecraft used it for a test. The craft is named New Horizons. It is on a trip to Pluto. Some big telescopes have not taken a photo of it yet. This is because the cluster is so large. It would take too many photos to see it all.

Messier 7 is a beautiful group of stars. We call this an open cluster. It sits in the constellation of Scorpius. You can find it near the stinger of the scorpion shape. Many people can see it without a telescope. It is the southernmost object in the Messier list. This makes it a special part of our night sky.

This cluster works by holding many stars together. It is about 25 light years across. The stars are 980 light years away from us. The cluster has a combined mass. This mass is about 735 times the mass of our Sun. It is about 200 million years old. The stars inside have much like our Sun. They contain similar amounts of elements besides hydrogen and helium.

People have looked at these stars for a long time. A Greek-Roman astronomer named Ptolemy saw it in 130 AD. He thought it was a nebula. Later, Giovanni Batista Hodierna saw it before 1654. He counted 30 stars in the group. In 1764, Charles Messier put it on his list. He called it the seventh member of his list. John Herschel called it a coarse cluster of stars.

There are many specific facts about these stars. Telescopes show 80 stars in a small view. This view is 1.3 degrees across. In China, astronomers called the cluster Yú. This name means "the Fish." One very bright star is HD 162391. It has a magnitude of 5.53. Another bright star is HD 162496 with a magnitude of 5.68. There are over a thousand likely stars in the whole group.

Modern tools help us see the cluster in new ways. In 2006, the New Horizons spacecraft used it for a test. This was the first light image for its LORRI telescope. This craft is traveling to Pluto. The Hubble Space Telescope has not photographed it yet. This is because the cluster is very large. It would take too many photos to see it all. Hubble has a small field of view for such big things.

Messier 7, also known as M7, is a large open cluster of stars. An open cluster is a group of stars that stay close together in space. This specific cluster is located within the constellation of Scorpius. It is easily visible to the naked eye near the stinger of the scorpion. Because of its position, it is the southernmost object in the Messier catalog.

The cluster consists of many individual stars held together by gravity. It has a combined mass of approximately 735 times the mass of our Sun. The cluster is estimated to be about 980 light years away from Earth. This distance means the cluster has an actual diameter of about 25 light years. While there are over a thousand likely member stars, telescopes show about 80 stars within a small field of view. This specific field of view is only 1.3 degrees across.

Scientists study the composition of the stars to understand their nature. The stars in Messier 7 have a chemical makeup similar to our Sun. They contain a similar abundance of elements other than hydrogen and helium. The cluster is roughly 200 million years old. Within the group, many stars have already evolved away from the main sequence. The main sequence is the stage where stars spend most of their lives. The most luminous stars on this sequence are around spectral class A0.

Humans have observed this cluster since ancient times. In 130 AD, the Greek-Roman astronomer Ptolemy recorded it. He described the cluster as a nebula, which is a cloud of gas or dust. Before 1654, the Italian astronomer Giovanni Batista Hodierna observed it and counted 30 stars. In 1764, the French astronomer Charles Messier added it to his famous list. He named it the seventh member of his catalog of comet-like objects. Later, the English astronomer John Herschel described it as a cluster of coarsely scattered stars.

Different cultures have given the cluster unique names. In Chinese astronomy, the cluster is identified as Yú, which means "the Fish." There are several very bright stars within the cluster that astronomers track. One bright member is HD 162391, which has a magnitude of 5.53 and a spectral type of G8/K0III. Another is HD 162496, with a magnitude of 5.68 and a spectral type of K1III. Other notable stars include V957 Sco and HD 162515. These stars help astronomers understand the brightness and types of stars in the group.

Modern technology provides new ways to look at Messier 7. On August 29, 2006, the cluster was used for a very important test. It was used for the "first light" image of the LORRI telescope. LORRI is the Long Range Reconnaissance Imager on the New Horizons spacecraft. This spacecraft is currently on a mission to Pluto. Using a known object like M7 helps scientists ensure the telescope is working correctly.

Interestingly, Messier 7 is one of the few Messier objects not photographed by the Hubble Space Telescope. As of January 2022, it remained unphotographed by Hubble. This is not because it is unimportant, but because of its size. The cluster has a large angular diameter. Hubble has a very small field of view. To photograph such a large object, Hubble would need to take thousands of separate photos. For example, a panoramic photo of the Andromeda Galaxy required about 7,400 exposures and 400 movements. Messier 7 is simply too large for Hubble to capture easily.