Costellazione Lira, stelle principali e mitologia
La Lira (in latino Lyra) è una piccola costellazione dell'emisfero boreale, ben rappresentata da Vega (Alpha Lyrae), che, dopo Arturo (Alpha Bootis), è la stella più splendente dell'intero emisfero nord. Si tratta di una delle 88 costellazioni moderne ed era già presente nella elencazione di Tolomeo. Sebbene non sia particolarmente estesa, la luminosità di Vega ne consente una pronta collocazione nel cd. Triangolo Estivo (insieme alle costellazioni dell'Aquila e del Cigno).
Main stars of the constellation Lyra
The most important stars in the constellation Lyra are:
– α Lyrae (Vega), which in Arabic means attacking eagle: it is the second brightest star in the northern hemisphere (the fifth overall among the stars observable in the night sky), as well as among the closest to our solar system, as it is just 25.3 light years away; furthermore, it is the first star to have been photographed.
– β Lyrae (Sheliak), from the Arabic Harp: it is a blue star, with a magnitude of 3.45; it is an eclipsing variable that constituted the prototype for the foundation of a specific class of stars.
– γ Lyrae (Sulafat), which in Arabic indicates Tortoise: this name derives from the composition of tortoise shell which was used as the sounding board of the lyre.
Within the constellation of Lyra there are numerous variable and double stars of particular importance.
In particular, the RR Lyrae constitutes a red variable star, visible even to the naked eye: it is a star similar to the Cepheids, which has given its name to an entire class of stars (the RR Lyrae variables), used as standard candles in determining the distance of globular clusters (in which it is very common to find them).
The constellation also has numerous double stars, some of which are among the best known:
– δ Lyrae, double star formed by a blue-white star and a red giant.
– ε Lyrae, a very well-known pair of stars, since it is visible to the naked eye and can be broken down into two main components with the use of ordinary binoculars, both of which are blue in colour. However, using more powerful instruments, it is possible to appreciate the fact that the two components are in turn formed by two pairs, which has given the system the name Double Double, one of the most famous multiple stars in the sky.
Lyra is particularly close to the Milky Way, which makes it possible to observe many deep space objects within the constellation’s figure; among these we can mention M57, also known as the Ring Nebula: its brightness and its clear disk shape have made it one of the best-known nebulae.
Mythology of the Lyre
The Lyre takes its name from the instrument of the same name of Orpheus, a legendary musician of ancient Greece made known by the story of his descent into Hades.
Orpheus’ Lyre was invented by Hermes, son of Zeus and Maia (one of the Pleiades), who built it from a tortoise shell: having cleaned the shell, Hermes created holes along the edge, inserting seven strings (corresponding number to that of the Pleiades), finally equipping the instrument with a plectrum with which to play the strings.
According to the story provided by Eratosthenes, Hermes stole some cattle from Apollo: to appease the wrath of the powerful sun god, the former bewitched him with the sound of the lyre, causing him, however, to fall in love with the music produced by the instrument, ending by leaving the cattle to Hermes in exchange for the lyre. Subsequently, Apollo gave the Lyre to his son Orpheus (born from the union with the Muse Calliope), who made use of its melodies in numerous adventures: his ability to enchant stones and waterways with his songs is legendary, as well as to calm the minds of angry people, it is said that the sound of his lyre even attracted the trees down from the mountains towards the coasts of Thrace.
The myth of Orpheus and Eurydice is very well known: after the death of the nymph, the former descended into Hell to ask for the young bride to be resurrected; it was the sound of his lyre that convinced the god of the afterlife, who granted Orpheus the possibility of leading his bride towards the world of the living on the condition that the musician did not turn around to look at the bride along the way. During the journey, Orpheus led the way to Eurydice in the dark corridors of the underworld by playing the lyre. However, a few meters before reaching his destination, overcome by the temptation to make sure that Eurydice was actually following him, Orpheus turned around, causing the bride to be sucked back into her shadow forever. Devastated, Orpheus wandered the countryside for the rest of his days, playing melancholic music on his instrument.
According to what Ovid tells, it seems that the numerous women who had proposed to him as his wife, being constantly rejected, ended up ganging up against him, angry, with the aim of killing him. Upon his death, however, Orpheus was able to reunite with his beloved Eurydice and the Muses placed the Lyre among them following the advice of Zeus, their father.
In honor of his Greek origins, Ptolemy named the brightest star in the constellation Lyra. The current name, Vega, however, was given by the Arabs, who named it al-nasr al-waki, that is “attacking eagle”, since in their atlases they considered this constellation represented as a bird with closed wings, ready to swing a lyre. Conversely, in the constellation of Aquila, the conformation of the star Altair and the others nearby gave the figure of a bird with spread wings.
The Lyre is also present in the Chinese and Japanese tradition: in these oriental cultures the Eagle was considered as a shepherd (Hikoboshi) and the Lyre as a weaver (Orihime); taken by passion for each other, they ended up neglecting the celestial tasks assigned to them (the production of fabrics for the creation of clothes for the gods and the care of grazing livestock). For this reason, the two were punished, dividing them at the two ends of the sky so that they could no longer meet, except once a year: in fact, on the seventh night of the seventh Moon a bridge of birds crosses the Milky Way, allowing the two lovers living together for a brief moment.
Characteristics and observation of the constellation
Since it is a summer constellation, being part of the Summer Triangle together with the Eagle and Cygnus (with which it crosses in July) and taking into account the extreme brightness of Vega, Lyra is practically impossible not to find in the night sky. In particular, Vega constituted the western and brightest vertex of the triangle; furthermore, to the east of Lyra lies the luminous trail of the Milky Way.
Lyra is a northern constellation, so it is easily observable at our latitudes, particularly on summer evenings, around 9 pm; However, it is also visible in the months from May to the end of December, while its zenith occurs at the beginning of September. In the southern hemisphere it is observable in its entirety only at altitudes not too southerly, in particular in the period between June and September.