Every year August brings with it the Perseid meteor shower, one of the most famous and most active meteor showers , which is especially attractive because it occurs at a time when a large part of the population is on vacation and, especially, in which you want to stay at night observing the night sky, because the weather conditions accompany .
This shower of stars receives two names, Perseids, the most usual and astronomical, and tears of San Lorenzo , more traditional. The first name has a functional origin: the fireballs in this meteor shower appear to originate near the constellation Perseus . This constellation is located in the sky of the northern hemisphere , between the constellations of Andromeda and Auriga, as well as between the constellations of Cassiopeia and Taurus. This constellation already existed in antiquity, as it was part of the 48 constellations that Ptolemy classified in the second century AD The Perseids seem to come from Perseus because that is the direction in which the Earth moves in its movement around the Sun during the time in which this meteor shower occurs.
The second name has a more romantic origin and honors San Lorenzo . This deacon of Rome, born in Huesca during the third century AD, was martyred and burned at the stake during the persecution of Christians that would end with the martyrdom of the then Pope Sixtus II. San Lorenzo died on August 10 and that is why his saints are celebrated on that day. Apparently the Perseids would be the tears that he shed during his death .
Of course, all this tells us about the culture and historical events that surround this meteor shower, but not about the true astrophysical origin of the event in question. This origin is neither divine nor has anything to do with the Perseus constellation or any of the stars that form it, but is located in the Swift-Tuttle comet . This comet was discovered in 1862 during an approach to Earth by astronomers Lewis Swift and Horace Parnell Tuttle. During this close approach the comet became as bright as the Pole Star . It was predicted from observations and measurements in 1862 that it would return through the inner solar system between the years 1979 and 1983 , but it did not. The comet ended up returning in 1992, with which it was definitively identified as the protagonist comet of some historical observations, such as those made in China in the year 188 . In its approach in 1992 it was not visible to the naked eye, since it did not get to be less than about 170 million kilometers from Earth, greater than the distance that separates us from the Sun. However, this approach was enough to cause, at The following year, a considerable increase in the activity of the Perseid meteor shower, which reached the rate of 300 fireballs per hour.
We now know from observations after the 1992 flyby that the comet is about 26 kilometers in diameter and takes about 133 years to complete a full orbit around the Sun. This orbit is also highly elliptical, meaning that the difference between the point closest point of its orbit, the perihelion, and the furthest point, the aphelion, is considerable. During perihelion , Swift-Tuttle gets to be slightly closer to the Sun than the Earth , at about 144 million kilometers from the star. During aphelion however, the comet can reach a distance of more than 51 times the distance between Earth and Sun , thus reaching beyond Neptune and even the outermost parts of Pluto’s orbit . In addition, the comet is in a 1:11 resonance with Jupiter, completing one orbit around the Sun for every 11 orbits of the gas giant.
Comet Swift-Tuttle is by far the largest of those bodies in the solar system whose orbit regularly brings it close to Earth . This makes it potentially dangerous, due to the possibility of a collision between both bodies. Calculations made after the 1992 observations indicated that the comet would pass extremely close to Earth on its next visit , in the year 2126. However, it was later seen that these calculations carried errors from an earlier calculation made in 1973. When it was identified that this comet was the same one that was observed in China almost two thousand years ago and when these data were introduced into the calculations, it was seen that the risk of collision decreased considerably According to the current calculation, the comet Swift-Tuttle will pass more than 22 million kilometers (about 57 times farther than the Moon) from Earth on August 5, 2126 and will have no chance of colliding with the planet for the next two thousand years.
If it were to collide, it is estimated that this comet would impact with about 27 times more energy than that corresponding to the meteorite that killed the dinosaurs 66 million years ago.
Reference:
Yau, K. et al, 1994, The past and future motion of Comet P/Swift-Tuttle, Monthly Notices of the Royal Astronomical Society. 266, doi:10.1093/mnras/266.2.305
