Gemini is one of the zodiacal constellations of the night sky, known to people even before our era. It is clearly visible in the Northern Hemisphere from December to May. In clear cloudless weather you can see up to 70 stars, the brightest of which are Pollux and Castor.
Gemini constellation
Dioscoura's twins Castor and Pollux are the heroes of ancient Greek mythology. They participated in the campaign of the Argonauts, Calydon hunting and the Olympic Games, which Hercules arranged. In ancient Greece, they were considered the savers of navigators and patrons of soldiers, in Rome they were a symbol of military courage.
The constellation was already known in antiquity, and was indicated in the Almagest by Claudius Ptolemy. According to legend, Zeus placed him in heaven so that the brothers tied to each other never parted. Arabs compared these stars to Gemini. Star Pollux they called "the head of the second twin."
In the sky, the Constellation appears in latitudes from +90 to -54 degrees. It occupies an area of 514 square degrees, and is located in the "company" of Cancer, Lynx, Small Dog, Taurus, Charioteer, Orion and the Unicorn.
Alpha Twins
Castor (α Gem) is the alpha and second brightest star in the constellation Gemini. According to the spectral type, it is characterized as A2Vm - the blue star of the main sequence. Its radius is almost three times greater than that of the Sun, and the temperature is about 9000 Kelvin. It is 50 light-years distant from our planet. The apparent magnitude of the star is 1.58, the absolute - 0.59 / 0.61. Moreover, the smaller the digital value, the larger the value.
The Castor star is a multiple, this feature of it was noted in the XVII century. Later it turned out that it is not just binary, but represents a system of three components, each of which is a spectrally binary star. The largest is Castor a, directly related to Castor b. The period of their circulation is about 350 years.
There is a so-called “moving group of Castor stars”. These are 15 stars that are combined with the Gemini alpha by the gravitational field, and move with it in the same direction. They have different sizes, but the same origin and almost the same age. The Castor group includes the star Vega, Fomalhaut, k Phoenix, α Cepheus, 14 Hares, several stars of Libra and Gliese.
Beta twins
Mark the stars with the letters of the Greek alphabet was invented by the astronomer Johann Bayer, who lived in the XVI-XVII centuries. According to his system, the more luminosity (visible brightness) luminaries possess, the older the letter in the alphabet. Thus, alpha is the most visible star in the sky, and further on waning.
But with Pollux it turned out quite differently. This is one of the brightest stars in the sky and the brightest in the constellation Gemini. However, it is in second place and is listed as "beta." And all because of the fact that it is located south of Castor on the ecliptic coordinate system.
Among all the visible luminaries of the night sky, the Pollux star takes 17th place in its brilliance. So, she surpasses the Alpha of Leo, Southern Fish and Swan, as well as Beta of the Southern Cross. You can observe it with the naked eye, without additional optical devices.
Pollux Features
The star is an orange giant and belongs to the spectral class K0 IIIb. Its temperature is 4865 degrees Kelvin, and the absolute magnitude is 1.09. All these characteristics indicate that the Pollux star is in the final stages of evolution.
It has already moved away from the main sequence stars, its hydrogen is no longer involved in thermonuclear reactions, remaining “passive”. However, a helium core still supports the reaction. Over time, the helium reserves will come to an end, and the star, shrinking and dropping the shell, will turn into a white dwarf with a very faint glow. Such a transformation must occur within 100 million years.
Now the luminosity of Pollux exceeds the solar by 32 times, and it is about forty light years distant from us. It is assumed that she is a variable star, that is, her brightness is not constant and ranges from 1.10 m to 1.17 m. Eleven years ago, scientists discovered that there is an exoplanet in its orbit that revolves around it with a period of 590 Earth days.
Other objects in the constellation
In addition to Pollux and Castor, there are 12 more stars in Gemini, brighter than the third magnitude, several dozen more have a magnitude brighter than 6.5 m. About four of them have discovered planets. Gemini is ideal for observing a constellation, a huge number of its objects can be seen even without a telescope, for example, orange k Gemini with a green satellite or spectrally double Alhena.
Another interesting star visible with the naked eye is This Gemini or Propos. It is a triple star system with a period of 2,983 Earth days. It is located 380 light-years from the Sun. It has a variable brightness from 3.1 m to W, 9 m. The transition from one value to another is quite possible to trace, observing the luminary for 233 days.
Star HD 50692 or 37 Gemini - a yellow dwarf, like our Sun. It is 56 light-years from Earth. Its age exceeds 5.5 billion years, and the mass is almost equal to the sun. In 2001, a message from the Crimean radar was sent to her system. It will be delivered to the target in 2057.
Geminid Streams
From December 4 to December 17, the Geminid meteor shower passes near the Castor star, named after the Latin name of the constellation Gemini. It has been known since the 19th century. Its average speed is 35 km / h. It is not too big, as meteors are moving in the same direction as the Earth.
The thread is considered one of the most powerful. Bright fireballs and meteors often appear in it. Geminid Peak falls on December 13-14, at which time about one hundred meteors pass in an hour. In 2011, there were 200 per hour.