Quite often, when it comes to exoplanets, their names begin with the word Gliese. Have you ever wondered why this is? In fact, this is the name of a German astronomer who compiled a catalogue of the stars closest to Earth. It is around them that all these bodies revolve.
Have you ever heard of the planet Gliese 581 d, the planet from which a signal from extraterrestrial civilisations was supposedly received? Or about its neighbour Gliese 581 g, which is ideal for human life. Or about Gliese 667C s, a planet in a system of three dwarf stars. Or about Gliese 867 d, one of the lightest known exoplanets.
Why do so many exoplanets have the word ‘Gliese’ in their names and what does it mean? In fact, this is the name of a German astronomer who, although he lived a rather interesting life, was engaged in such uninteresting things in science that it became world famous only with the discovery of the first exoplanets.
Wilhelm Gliese was born on 21 June 1915 in a town that was then called Goldberg because it was part of the German Empire. Now it is Złotoryja in Poland. Gliese himself was German, the son of a local judge. In 1933, he began studying astronomy at the University of Wroclaw and later moved to Berlin.
There he continued his studies and worked at the Astronomical Computing Institute. But then the Second World War broke out, and the young astronomer was mobilised and sent to fight on the Eastern Front. No details of what happened to him there have been preserved. We can only assume that he had many chances of dying.
Nevertheless, Gliese survived and in 1945 was taken prisoner by the Soviets. It is worth noting that the USSR treated captured German soldiers as slaves, poorly fed them and used them for various hard labour.
However, Wilhelm survived this and returned to Germany in 1949. His hometown was now in Poland, and Germans were not welcome there. The only thing left was his home scientific institute, which had moved to Heidelberg. So, it was there that the astronomer went.
Peter van de Kamp
It was in Heidelberg that Gliese met the astronomer Peter van de Kamp, and it was this meeting that played a decisive role in his future life. Van de Kamp was engaged in the most boring field of astronomy for ordinary people – astrometry. For many years, he meticulously recorded the positions of tens of thousands of stars in the sky, studying their own motion vectors and changes in brightness.
Van de Kamp was especially interested in the stars closest to us, many of which, despite their short distance, were not visible to the naked eye. It was the study of their movement in space that led van de Kamp to the scientific work that made him famous.
Van de Kamp said that some of them, including Barnard’s star, have irregularities in their motion that indicate that planets may orbit them. This was one of the first scientific papers to prove that planets existed around other stars. For a long time, it remained controversial, and then van de Kamp’s assumptions were refuted. Later, a planet was found near Barnard’s star, but not where he said it would be.
And it was this controversial man who aroused Gliese’s interest in the Sun’s immediate surroundings, so he spent the next 40 years compiling a catalogue of the stars closest to us.
Star catalogues
It is worth noting that stellar catalogues were not something new when Gliese began his work on the study of nearby stars in 1951. On the contrary, they can be considered one of the foundations of astronomy. Even the ones visible to the naked eye are not easy to count, but astronomers need to take them all into account to study the starry sky, and no one head can hold all this information.
That is why astronomers have been compiling lists of stars with their coordinates and sometimes some other parameters for several centuries. They are called catalogues.
In the middle of the twentieth century, hundreds of thousands of stars were already known, and work was underway to compile the fourth and fifth editions of the Fundamental Catalogue. Wilhelm Gliese took an active part in this work. However, all these catalogues said a lot about how the stars are located in the Earth’s sky and practically nothing about how they are located in space relative to the Sun.
Source: early-astronomy.classics.lsa.umich.edu
As early as the 1950s, astronomers realised that most of the stars around the sun are red dwarfs, which cannot be seen without a telescope. But there are also some quite visible luminaries. So what does the full list of stars located near us look like?
The answer to this question was given by the same boring astrometry that Gliese and van de Kamp were engaged in. Thanks to them, it was possible to calculate more or less accurately how far away a particular barely visible star was from us.
In 1957, all of this work was translated into the first Catalogue of Nearby Stars, also called the Gliese Catalogue. Its first edition contained only 915 stars and each of them was assigned a serial number.
The Gliese catalogue did not become a worldwide sensation. What difference does it make where those red dwarfs are, which are not visible in the sky, when everyone is discovering pulsars, quasars and black holes? However, the scientist continued his work and in 1969 released the second edition of the catalogue, which contained data on 1529 stars. They are located at a distance of up to 72 light-years from us.
Once again, only astronomers remembered Gliese. They began to help Gliese. In the United States, Richard Wooley’s group was doing this. In Heidelberg, Hartmut Jahreiß worked with Gliese. Together, in 1979, they published a new catalogue in which close stars are designated as GJ plus a few digits. If you come across a star with this name, you should know that these two letters stand for Gliese-Jahreiß.
Years passed. Gliese continued to research and catalogue nearby stars. In the 1991 edition of the catalogue, there were already 3,800 stars close to the Sun. One of the asteroids in the Solar System was named after Gliese. However, the name of the boring astrometrician remained unknown to the general public.
In 1997, Hartmut Jahreiß and his colleagues created ARICNS, one of the world’s first electronic star databases, which was made available to astronomers online. It was based on the catalogue that Wilhelm Gliese had started to compile. However, the astronomer himself did not live to see it. He died in 1993, having lived a long but seemingly unremarkable life.
Gliese and nearby stars
Gliese’s name became truly famous after his death. In the second half of the 1990s, astronomers began to discover the first planets outside the Solar System. Interestingly, they used and still use methods that are essentially astrometric. Astronomers measure the fluctuations in the movement of stars in space and their brightness, only in more precise ways than Van de Kamp did.
But all these methods still have significant limitations. The easiest way to find planets is in stars that are not very bright themselves, but are relatively close to the Earth. But these are the same stars that are listed in the Gliese and Gliese-Jahreiß catalogues.
Since few people were interested in all these red dwarfs before, it is not surprising that these catalogues were used to name discovered planets, adding a small letter of the Latin alphabet starting with b to the star designation.
To be precise, in fact, the vast majority of stars around the Sun have designations in the Gliese catalogue. For example, Proxima Centauri is GJ 551, and Sirius is GJ 244. Another thing is that no one uses these designations.
But even without them, there are dozens of stars that are usually named in the Gliese catalogue. It should come as no surprise that whenever there is news of the discovery of a planet close to us, the name of the German astronomer is mentioned in the title. After all, his catalogue contains precisely those stars around which the discovery of planets is most likely to be noticed outside the astronomical community.
And it is quite possible that this is not the end. Someday, humanity will organise the first interstellar journeys. They will be aimed at the most promising luminaries. Those that are not far from us and definitely have planets. And to a large extent, these will be the same stars that Wilhelm Gliese once included in his catalogue.
