They began to cross the night sky in the second half of July, but the real spectacle of the perseids takes place in mid-August. They receive the popular name of ‘tears of san lorenzo‘ because it is easy to see them on the 10th of this month, feast of the Spanish martyr of the same name, but in reality their peak time is between the 11th and 13th. Specifically, this year will be the night of Friday, August 12 to Saturday, August 13with a peak around 00:03 h (Spanish peninsular time), according to the Instituto de Astrofísica de Canarias (CAR).
The Perseids are a rain of meteorscommonly called “fleeting stars”, of cometary origin and visible from the entire northern hemisphere in midsummer.
Its activity rate can reach 200 per hour, although the normal thing is to see about a hundred, and this year, moreover, it will be much less because only on the 12th there are full moonwhich will make observation difficult.
“If conditions were ideal, about a hundred shooting stars could be seen per hour, but the brightness of the Moon will be one of the factors that will cause the actual number of visible Perseids to drop to about fifty”, he points out. Jose Maria Madedoresearcher at the Institute of Astrophysics of Andalusia (IAA-CSIC).
In any case, the exact number of meteors observable per hour is highly variable. Specific predictions about their specific number, depending on the day and time, are difficult to make and are usually affected by high uncertainty, clarifies the National Astronomical Observatory (NO-IGN).
Radiant to the constellation of Perseus
The Perseids can be seen anywhere in the sky, although they appear to come from a specific area, their radiant: a constellation of perseus (hence its name). For observers located on the Iberian Peninsula (latitude 40º north), the Perseid radiant is located northeast above the horizon throughout the night.
The ‘radiant’ of the Perseids: the constellation of Perseus, from which it seems to radiate or come. / National Astronomical Observatory (IGN)
To enjoy these ‘shooting stars’ it is not necessary to use telescopes or any other type of optical instrument that limits the field of view. It is enough to observe the sky from a place as dark as possible and away from the light pollution of populations. It is preferable that there are few obstacles in sight, such as buildings, trees or mountains.
Look for dark skies
It is convenient to direct the gaze also towards the darkest areas, in the opposite direction to the position of the Moon if the observation is made when the Moon is present. The most comfortable thing is to lie down and wait for your eyes to get used to the darkness.
“As in previous years, you have to find a place far from urban centers, fix your eyes on a point in the sky and wait patiently to see some of the Perseids’ traces of light”, he says. Miquel Serra Ricarastronomer from the IAC, who confirms that it is not a good year for the Perseids: “The full moon will make it difficult to see the faintest meteors, so their frequency will be lower and we will only observe the brightest ones, which continue to be impressive.”
Serra-Ricart, in collaboration with Portuguese institutions, will relay on the night of the 12th to the 13th of August, the maximum activity of this shower of ‘shooting stars’ from La Palma and Madeira, a joint initiative to raise public awareness of the light pollution problem.
Perseid Rain from the Teide Observatory (Tenerife). / MR Alarcón / D. Padrón
The Trail of Comet 109P/Swift-Tuttle
The Perseid meteor shower is produced by the impact on our atmosphere of particles left by the Comet 109P/Swift-Tuttlewhich has a period of 133 years and last passed close to the Sun in 1992. This object was discovered in 1862 and, with a size of approximately 26 km in diameterit is the largest that periodically approaches the Earth.
When describing its orbit around the Sun, the comet leaves a trail of gases, dust and debris (rocky material). Every summer the Earth finds that cometary trail and some of the rock fragments (meteoroids) are trapped by their gravitational field. In this encounter, some particles disintegrate as they enter the Earth’s atmosphere at high speed, creating the colored luminous lines that receive the scientific name of meteors.
“Most of the meteoroids that fly off this comet are as small as a grain of sand, or even less. When they cross our planet, they enter its atmosphere more than 210,000 kilometers per hourwhich is equivalent to traversing our country from north to south in less than twenty seconds”, compares Jose Luis Ortizresearcher at the IAA-CSIC.
At these speeds, the collision with Earth’s atmosphere is so sudden that the temperature of these particles rises to about 5,000°C in a fraction of a second, whereby they disintegrate, emitting a flash of light called a meteor or, more popularly, a star. falling. Therefore, they are not real stars, but glowing particles.
Disintegration occurs at high altitudes, normally between 100 and 80 kilometers above ground level. Larger particles (pea-sized or larger) can produce much brighter shooting stars, called bolides or fireballs.