The Perseid meteor shower arrives

The Perseids are produced by the impact in our atmosphere of fragments of the meteoroid cloud of Comet 109P / Swift-Tuttle, and are also recorded on the surface of the Moon. During the peak, around August 11, up to fifty perseids per hour can be observed in places away from light pollution


During the second half of July the Perseids began to cross the night sky. At the moment, only between one and two events can be observed every hour, but the true astronomical spectacle will take place in mid-August, when this meteor shower will reach its maximum activity: in places far from the light pollution of the big cities, up to fifty perseids per hour.

The Perseids, one of the classic astronomical spectacles of the summer in the Northern Hemisphere, originate from Comet 109P/Swift-Tuttle. This comet completes an orbit around the Sun approximately every 133 years and, each time it approaches our star, the Swift-Tuttle heats up, emitting jets of gas and small solid particles that form the comet's tail. Every year, between the end of July and the end of August, our planet crosses the remains of this tail, causing these particles, called meteoroids, to collide with the Earth's atmosphere at high speed.

As the Earth enters this cloud of meteoroids that the comet leaves behind, the number of particles is increasing, so that the activity of the perseids rises. In 2021 that activity will peak during the night of August 11-12. However, during the night before and after the activity of the Perseids will also be high, which will allow us to see a large number of shooting stars. The Moon, which reaches its new phase on August 8, will be at the beginning of its first quarter phase, so its brightness will be very low and will not interfere with observation.

“If the observation conditions were ideal, they could be seen on the order of one hundred shooting stars per hour, but the brightness of the Moon will be one of the factors that will cause the real number of visible Perseids to drop to about fifty", points out José María Madiedo, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC).

“Most of the meteoroids released from 109P/Swift-Tuttle are as small as a grain of sand, or even smaller. When they cross with our planet, they enter the Earth's atmosphere at a speed of more than 210,000 kilometers per hour, which is equivalent to traveling our country from north to south in less than twenty seconds”, points out José Luis Ortiz, researcher at the IAA- CSIC.

At these speeds, the collision with the atmosphere is so abrupt that the temperature of these particles increases to about five thousand degrees Celsius in a fraction of a second, so they disintegrate, emitting a flash of light that is called a meteor or shooting star. This disintegration occurs at high altitude, usually between 100 and 80 kilometers above ground level. Larger particles (the size of a pea or larger) can produce much brighter shooting stars, which are called bolides or fireballs.


To enjoy the Perseids it is not necessary to use telescopes or any other type of optical instrument. It is enough to observe the sky, preferably from somewhere as dark as possible and away from the light pollution of the cities.

These shooting stars can appear anywhere in the sky. By prolonging their trajectory backwards they will appear to come from a point located in the constellation of Perseus, from which their name comes. This point is called radiant. Since the constellation Perseus rises above the horizon after dark, the probability of seeing Perseids increases as the night progresses and peaks near dawn.


The Perseids also hit the Moon. Unlike Earth, the Moon lacks an atmosphere to protect it, so meteoroids collide directly with the lunar soil at more than 210,000 kilometers per hour. This causes the meteoroids and part of the lunar soil in which they impact to be abruptly destroyed, thus forming a new crater.

In each of these collisions, a brief flash of light is also released that the human eye cannot perceive directly, but that can be detected from Earth with the help of telescopes. “The study of these flashes allows astrophysicists to obtain very relevant data on the collisions that occur against the Moon and against the Earth. For this reason, during the nights of greatest activity of the Perseids, our telescopes of the MIDAS project will also point to the Moon to be able to record how the particles detached from Comet 109P/Swift-Tuttle disintegrate against the lunar soil”, concludes José María Madiedo.



Instituto de Astrofísica de Andalucía (IAA-CSIC)
Unidad de Divulgación y Comunicación
Silbia López de Lacalle - sll[arroba] - 958230676