If you have ever seen a shooting star on a clear night, surely someone has invited you to make a wish. However, it is a natural phenomenon without any magical connotation, beyond its great beauty.
What is really a shooting star? Where do these shiny moving bodies come from? How and when can we observe this astronomical phenomenon?
Meteor shower or shooting stars?
Although we popularly call them shooting stars, they are not really stars but particles of incandescent dust. To understand why, it is important to first distinguish between meteoroid, meteor and meteorite.
A meteor is the astronomical phenomenon that occurs when one or more particles of matter (meteoroids) enter the atmosphere at high speed. These meteoroids, which are usually very small (between a tenth of a millimeter and a few centimeters), are fragments of dust, ice or rocks that wander through space.
Due to the effect of our planet's gravity, if their trajectory is close enough, they are attracted and rush towards Earth, colliding at high speed with the air molecules in the atmosphere. Due to friction, they reach very high temperatures and become incandescent, producing a luminous and brilliant trajectory on their descent that makes them resemble stars.
The duration of this phenomenon is usually very short (fractions of a second, hence the term 'fleeting') and will depend on the size, speed and composition of the particles.
Meteors begin to emit light about 100 kilometers above the earth's surface. Normally they stop being seen when they have been totally consumed (when they reach about 60-70 km in height).
Therefore, since they are not really stars, the most appropriate – although less romantic – would be to call them meteor showers instead of shooting stars.
Sometimes, with a lot of luck, we can see some huge and bright meteors. They look like balls of fire and leave a luminous trail that lasts several seconds, even minutes, even producing sound phenomena and explosions. These meteors are called fireballs.
If the meteoroids, the particles that enter the atmosphere, are large (initial mass greater than 1 kg) they may not completely disintegrate. If any fragment reaches the surface of the planet we speak of meteorites (stones that fall to us from space). There are many collections with recovered meteorites, and their study allows us to discover the composition of celestial bodies beyond Earth.
What is the origin of meteor showers?
Where do the particles from outer space that produce meteors come from? Some of these particles have existed since the formation of the solar system, but most are produced during the journey of some comets around the Sun.
As they draw their orbit around the Sun, comets (huge bodies of ice and rock), due to the effect of heat and solar wind, release into space a series of gases, dust and rocky materials that remain in an orbit very similar to that of the comet In this way, each kite forms a kind of ring with the fragments that it has released after each step.
If the Earth, in its orbit around the Sun, crosses one of these rings, some of these rocky fragments released by the comet are caught by the Earth's gravitational field and fall at high speed through the atmosphere forming the meteor shower
When can we observe meteor showers?
When we are on vacation, it may be that we find ourselves somewhere far from the light pollution of big cities and that we take advantage of going out in a relaxed way at night. If we are tempted to look up we will be amazed by the sight of stars, planets, galaxies, even the Milky Way. And maybe we will also be lucky enough to observe a shooting star.
But shooting stars can not only be seen in summer. In fact, each year there are fourteen meteor showers, of which ten can be seen at night. Each one is associated with the passage of a comet that has left a trail of meteoroids on its journey.
The most popular meteor showers are possibly the Perseids, also called the tears of San Lorenzo because their maximum activity, in mid-August, is close to this holiday. The parent comet of the Perseids is Comet Swift-Tuttle. The maximum rate of meteor fall usually occurs on August 13 (it can vary), with an average fall of about 100 meteors per hour.
But both the Quadrantids (visible in January), with a rate of 120 meteors per hour, and the Geminids (in December), also with a rate of about 120 per hour, are just as spectacular.
This rate of decline is what would be observed with the naked eye in a place where the radiant was at the zenith and the visibility conditions were optimal. So if we go out to observe a meteor shower, we should be temperate with our expectations and not be disappointed if we see less than expected.
It is important to know the concept of radiant of the meteor shower because it is the point in the sky from which the shooting stars seem to emerge at the moment of maximum occurrence. This point can be precisely defined in the form of astronomical coordinates, but it is also described as the region of the sky in which the constellation that gives the meteor shower its name is located. Like Perseus for the Perseids or Gemini for the Geminids.
- Find areas with little light pollution (therefore, and unfortunately, far from cities) from which the longest possible horizon is dominated.
- Have a lot of patience: shooting stars do not appear constantly or as soon as we start our observation.
- If possible, go out to observe on moonless nights or with a moon close to new moon.
- Know how to locate the reference constellation of the radiant (area where the meteors seem to come from).
- Lie down comfortably looking at the sky.
- Look at the naked eye. To observe this phenomenon we need to observe a wide region of the celestial vault, so it is not necessary (nor recommended) to use binoculars.
- Even if it is summer, bring warm clothes and supplies to comfortably endure the observation.
And if we can't see any meteors, we can always enjoy the wonderful experience of observing our sky.
This article has been published in 'The Conversation'.