Summer time, shooting stars time. Like every year, the appointment with the magical “tears of San Lorenzo” returns, the meteors of August better known as Perseids. One of the most anticipated astronomical events of the year, capable of arousing curiosity and interest among the general public, thanks to the summer period and holidays, perhaps spent under a clear and dark sky.
When to see shooting stars
Tradition links the phenomenon to the martyrdom of San Lorenzo, who according to tradition was burned on the grill in 258, whose anniversary is celebrated on August 10 and from which the popular name of the swarm derives; however, it is active for many days (between July 17 and August 24, with a rapid “collapse” after the maximum) around the true peak of visibility, which nowadays falls between August 11 and 13. At most, an average of up to 100 meteors can be observed per hour, provided that the observation is made in the second part of the night. Ideally, observations should be conducted from a dark place, since artificial light drastically reduces the number of visible meteors. No telescopes or other devices are necessary, since the naked eye is undoubtedly ideal for capturing the sudden flash of such luminous trails, thanks to natural panoramic vision.
What are the Perseids?
The Perseid meteor shower originates from the Swift-Tuttle comet, discovered in 1862. It was the Italian astronomer Giovanni Virginio Schiaparelli (the “father” of the Martian channels) who, in the 19th century, established a connection between the meteors and the comet in question, a mechanism of general interest for meteor showers. The phenomenon occurs precisely when the Earth passes near the intersection between its orbit and that of the comet in question, thus “diving” into the cloud of dust scattered by the latter along its path around the Sun. These grains of dust, penetrating the Earth’s atmosphere at great speed, burn due to friction, thus leaving the characteristic trail in the sky. This therefore reveals that it is not stars at all that are “falling”, but rather crumbs of the comet in question. Swift-Tuttle is a periodic plumed star, which returns approximately every 135 years. The last passage dates back to 1992. Meteors can be observed every clear night of the year, but it is possible to see them in greater numbers precisely in correspondence with these “orbital” encounters, when therefore there is a greater quantity of dust ready to enter the atmosphere. In these cases we speak of meteor showers: the one in August is only the most popular, but there are others of notable interest throughout the entire year.
The name of the Perseids comes from the position in the sky occupied by the radiant, or the point from which the meteors appear to emerge from a perspective: in this case, it projects in the direction of the constellation of Perseus, the famous protagonist of the autumnal firmament. However, the meteors appear throughout the sky: ideally retracing the trails of the Perseids backwards, they would converge precisely in the radiant, whose position is moderately variable over the course of the days. You can decide to look towards the constellation of Perseus, located halfway to the north-east at the end of the night, also in a wonderful area of the sky, or simply lie down on the ground and thus gaze towards the zenith, or the center of the sky.
The difference between the various “vintages”
As astrophysicist Gianluca Masi explains on the Virtual Telescope Project website, although it is a recurring phenomenon, not all “years” are the same. The number of meteors actually visible, while always interesting (with at least 50 meteors per hour close to the maximum), experiences significant fluctuations. First of all, the most intense showers are those close to the return of the comet, which supplies its trajectory with “fresh” dust. Furthermore, it can happen that during the period of maximum activity of the Perseids the Moon is present, perhaps close to its full phase, with a heavy negative effect on the visibility of the meteors. For example, last year, right around the date of the maximum, it was visible all night, thus resulting fatally invasive.
After a favorable 2023, in 2024 the observation conditions for the Perseids will still be favorable. The Moon, in fact, will be new on August 4, while the maximum is expected between August 11 and 12: on the evening of the 11th our satellite, not even having reached the first quarter, will set shortly after 11:00 pm, leaving the sky perfectly dark for the rest of the night, the most favorable night for viewing meteors. It can be observed at any time, remembering however that in the second part of the night there is a significant increase in meteoric activity, since at dawn the observer is on the part of the Earth that advances along its orbit towards the cometary dust, therefore it is as if he were seeing from the “windshield”, rather than from the rear “window” of our planet. Furthermore, towards dawn the radiant of the swarm will be high in the sky. This condition, together with the setting of the Moon, therefore guarantees good results.
Naked eye and camera
As mentioned, naked eye observation is undoubtedly the best, while it is important to choose an observation site as far away as possible from light pollution, the true enemy of sky observation and disastrous evidence of an immense waste of electrical energy.
Anyone with a camera capable of relatively long exposures can easily attempt to capture the brightest Perseids. The chances of success depend on various factors, such as the area of sky framed in the shot, the brightness of the lens used, the ISO sensitivity adopted. The larger the field of view, the greater the chances of intercepting the trail of a meteor. Super wide-angle lenses (with a focal length of less than 20mm) and “fish-eye” lenses are excellent in this sense, especially if they are bright (wider than f/4). It is useful to set the camera sensitivity to 800/1600 ISO, compatible with the noise of the camera. In this way, images are collected in sequence, each with an exposure of 30/60 seconds (check the degree of blackening of the sky background, which depends on the local light pollution), perhaps pointing in the direction of the radiant.