What is interesting about the constellation Gemini for astronomers

Astrologers claim that on May 22, the Sun entered the constellation Gemini. Astronomers know that in fact it will be there only on June 21, but for now our luminary has just begun to move around Taurus. By the way, unlike astrologers, people who study the starry sky can really tell a lot of interesting things about it.


1. Why “Gemini”

This name appeared back in the time of the ancient Sumerians, who were the first to see the silhouettes of two men in a group of stars. In their mind, these were the twin gods Lugalgirra and Meslamtea. The first was the god of the plague, and the second was the god of the underworld of the dead. 

The ancient Greeks adopted this idea from the inhabitants of Mesopotamia. They saw in the constellation of the Dioscuri brothers — Castor and Pollux, two heroes of ancient mythology who performed many feats and were very faithful to each other.

2. Which star of the Gemini constellation is the brightest?

When people talk about the constellation Gemini, they remember not one star as the brightest, but a pair of Castor and Pollux, which are located next to each other. In fact, the second of them has a greater brilliance. Its magnitude is 1.14, which makes Pollux the 17th brightest star in the Earth’s sky. In fact, this luminary is the orange giant closest to us. It is 8.8 times larger than the Sun in radius, and its mass is 47% higher than the solar one.

In 2006, a planet was discovered near Pollux — a hot gas giant, 2.3 times the mass of Jupiter. Its average distance from the central star is 1.64 AU, it makes one orbit around it in 590 days.

3. Are Castor and Pollux really located next to each other?

Although the two brightest Gemini stars appear very close in the sky (the angular distance between them is 4.5°), they are not gravitationally connected, and in fact they are about 18 light-years apart in space. At the same time, Castor is a multiple system consisting of at least six separate components: two white stars orbiting a common center of mass, and four red dwarfs circling around them in a complex dance.

However, Gemini also has a really close pair. We are talking about the star of this constellation. This system is located 280 light-years away and consists of white and red dwarfs. They orbit each other with a period of no more than 4 hours, while there is a flow of matter between them. 

This system is called a “dwarf nova” because flares occur in it with different frequencies, which resemble classic novae in their mechanism of occurrence, but at the same time are much weaker.

4. Which Gemini star is closest to us?

The closest star to us in the constellation Gemini is Gliese 251, which is also called Wolf 294 and HD 265866. It is located at a distance of 18.2 light years and is a rather large red dwarf.

The mass and radius of Gliese 251 are estimated at 36% solar, and its luminosity is only 1.7% of the corresponding indicator of the luminary. Therefore, this star is not visible even in amateur telescopes. Its surface temperature is 3500°C, which is quite typical for such objects.

In 2019, astronomers announced that they had found two exoplanet candidates near Gliese 251. However, the following year their existence was denied, but another celestial body was discovered orbiting this star in 14 days. It is four times the mass of our home planet and is most likely a warm super-Earth.

5. What is Geminga?

One of the neutron stars closest to us is located in the constellation Gemini. The distance to it from the Sun is about 800 light years. It was discovered in 1975 and was named Geminga. At that time, scientists were not immediately able to identify what it was, especially since it was not possible to visually identify the signal source with a visible object.

Actually, this is indicated by the name of the object, which in the Lombard dialect of the Italian language means “it’s not there.” It was only in 1992 that high-frequency pulsations were detected in Geminga, which made it possible to establish that it was a pulsar. According to scientists, this object is the remnant of a supernova that erupted about 300 thousand years ago.