The Geminids are one of the main meteor showers that take place each year, and are considered the most regular and intense (along with the Perseids in August, the famous Tears of Saint Lawrence).
It is a phenomenon that, in optimal dark conditions, can allow the visualization of up to 120 meteors (shooting stars) per hour at its peak activity, scheduled for the night of December 14 to 15. Furthermore, it so happens that, this year, the Moon will have reached its new phase on the 13th and, therefore, will be absent from the sky during the following nights, which implies ideal conditions for observation.
Meteor showers are caused by the entry into the Earth's atmosphere of a large number of small fragments left behind, usually by the passage of comets. These objects have in their composition many volatile materials (ice) that vaporize when they approach the Sun and drag dust particles into space. When our planet, in its orbit around the Sun, crosses a region close to the path of the comet, it encounters these fragments and the friction with the air causes them to disintegrate, generating the traces of light that we see in the sky.
The Geminids are active each year from approximately December 4 to 20, and their meteors are not caused by material released from a comet, but surprisingly from an asteroid (called 3200 Phaethon). This fact is not common, since asteroids have a more compact, rocky structure and with fewer volatile components in their composition than comets.
The Geminid meteor shower is one of the most productive of the year, with meteor rates that can reach 120 per hour under optimal visibility conditions. In particular, the observation of the Geminids is most favorable from the northern hemisphere.
Although it is always difficult to accurately predict the moment when the maximum activity of a meteor shower will occur, the Geminids usually generate a good number of shooting stars over several nights, especially those on the 13th, 14th and 15th. from December.
Specifically, the maximum is expected for the early morning of the 14th to the 15th, a little after midnight when the region of the sky from which the Geminid meteors appear to come is high above the horizon. This point is called radiant, and represents the place where the fragments of the parent object of a meteor shower enter the atmosphere. Precisely, the location in the sky of the radiant is what gives the phenomenon its name (in this case, the radiant is located over the constellation of Gemini).
This year, the observation conditions are optimal since the Moon will not be visible throughout the night (the new moon will occur on the 13th), so its absence will allow us to have the dark skies necessary to be able to perceive the shooting stars more weak.
Although the brightest Geminid meteors can be observed even from urban areas, to fully enjoy this meteor shower it is necessary to get away from the city lights. If movement is not possible, it is advisable to at least stay above the street lights, moving to elevated terraces.
Likewise, it is necessary to avoid exposure to light sources (especially white, such as that emitted by a mobile phone) to allow maximum dilation of the pupils and adaptation to good night vision.
Ideally, the place chosen for observation should be clear of nearby obstacles, so that it is possible to contemplate the largest possible region of the sky. Because although the material that generates meteors impacts the Earth at the radiant point, shooting stars can appear anywhere in the sky.
Geminid meteors can present coloration (mainly white and yellow, but sometimes also with shades of red, green or blue). The colors are caused by the presence of metals, such as sodium or calcium, in the asteroid fragments.
The asteroid 3200 Phaeton was discovered in 1983, and the calculation of its orbit allowed it to be related to the Geminid meteor shower.
Subsequently, observations made with the Arecibo radio telescope in 2017 showed that this object is about 6 kilometers in size. Based on its size and the proximity of its orbit to that of the Earth, the asteroid is classified by NASA as potentially dangerous.
But despite this classification, calculations indicate that there is no probability of an impact on our planet in the next few hundred years. In fact, the closest pass this century will occur on December 14, 2093, and at that time 3200 Phaethon will be about 3 million kilometers away from Earth.
The fact that 3200 Phaeton, being an asteroid, is the progenitor object of the Geminids has given rise to intense research to detect its possible particle emissions into space.
In 2009, NASA's STEREO satellite detected a tail extending behind 3200 Phaethon at the time of its closest approach to the Sun (perihelion). The discovery encouraged subsequent observations, which, although they suggested that the asteroid's tail could be composed mainly of sodium, did not detect any dust.
Therefore, this conclusion did not explain why the Geminid meteors are generated, and several hypotheses were then proposed: the fragments left behind by the asteroid could be the result of a past impact, or even 3200 Phaethon could be what was left. of an ancient comet.
However, on November 28, a study was published with the results of the analysis of the light reflected by 3200 Phaeton obtained by a group of researchers from the University of Helsinki. In it, scientists suggest that the asteroid's composition could be similar to that of a class of meteorites called CY carbonaceous chondrites, capable of emitting carbon dioxide, water vapor and sulfur when heated.
The orbit of 3200 Phaethon brings it closer to the Sun every 524 days, twice as close as Mercury does. At those times, its surface temperature can reach 750C, so, according to this study, the vaporizations caused near perihelion would be responsible for dragging the dust particles that end up becoming shooting stars in the December skies.
