It is known as meteor shower to the light effect produced when particles from the Solar System hit the Earth's atmosphere. The trace of light, visible between 3 and 5 seconds in the night sky, is caused by the ionization of atmospheric gases and heating by the friction between them and the particle.
The sight of these fleeting objects constitutes one of the most beautiful and easy to admire celestial spectacles, that is why a frequent question for all those fans is where do they come from??
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As in the construction of any human building, the formation of the Solar System left remnants that are still under its powerful gravitational influence. And that's not counting all the matter captured since then.
In the vicinity of the Solar System, beyond the limits of Pluto, dwell objects such as comets and asteroids.
When any of them intrudes close enough to the Sun, -almost always a periodic comet-, the gravitational interaction is so intense that part of their mass is lost, leaving a trace of matter in the orbit.
There are particles whose size ranges from microscopic grains to agglomerates of matter with good size - of about 100 km for example - called meteoroids. Every time the Earth approaches and intercepts the comet's orbit, the probability of encountering them increases.
Meteoroids penetrate the Earth's atmosphere at high speed, continually colliding with the atoms and molecules in their path and giving up part of their kinetic energy. Another part results in the heating of the same meteoroid.
At approximately 100 km altitude, the ionization of the atmosphere leaves a brief light trail that we recognize as a "shooting star" or "meteor". Heating almost always leads to complete evaporation from the body, but if it is very massive, one or more fragments - solid or fireballs- they manage to hit the ground.
Comet debris is the source of almost all known meteor showers. An exception are the Geminids, a shower left by the fragmentation of the asteroid 3200 Phaeton..
Shooting stars can be seen sporadically on any night, since the space through which the Earth's orbit passes is full of particles, in such a way that the trajectory can be practically any.
The most striking meteor showers take place during the times of the year when the Earth passes through the orbits of fractured comets, observing that a large number of them follow a trajectory that converges at a particular point in the sky: the radiant. This is a perspective effect.
In addition to the radiant, meteor showers are characterized by the rate of observable meteors per hour or zenith hourly rate (THZ), which may vary depending on the geographic location of the observer and other factors such as surrounding lighting. There are programs on the internet to calculate its value.
Finally, there is the distribution of magnitudes observed in the rain, called population index.
Among the rains with a well-established trajectory are the Perseids, so called because its radiant is in the constellation of Perseus, visible in early August.
Another very attractive rain is the Leonids, which is observable in November and has its radiance in Leo. In total there are about 50 swarms named after the constellation where the radiant is or the brightest and closest star.
The biggest showers are those with a high meteor / hour count and that year after year cross the night skies, having appeared regularly for hundreds of years..
The following is a list with the estimated release date, and later a guide to better enjoy them.
The major rains last a few days or weeks, as the Earth advances, while the maximum meteorites / hour occurs on a specific day or maximum two.
Although it is an arbitrary limit, it is considered a major shower when the count is greater than 10 meteors / hour.
There are rains that always have the same intensity, and others that from time to time become more intense, such as the Leonids every 33 years, even reaching the category of star storms, when the rate is 1000 or more meteors / hour..
Most of the meteor showers are well appreciated from both hemispheres, although depending on the radiant, there are some that are better seen from one or the other..
-Perseids (Constellation Perseus, between July 16 and August 24, maximum from August 11 to 13, between 50 and 100 meteors / hour, originated by Comet Swift-Tuttle).
-Leonidas (constellation Leo, from November 15 to 21, maximum November 17-18, its origin is the comet Tempel-Tuttle, variable number of meteors per hour, generally between 10 and 15. In 1833, 1866 and 1966 there was a maximum thousands of meteors per minute).
-Quadrantids (constellation of the Boyero, from the end of December to the first week of January, maximum on January 3-4, more than 100 meteors / hour, origin uncertain)
-Lyrid (constellation Lyra, a moderate shower visible from April 16 to 25, 10-20 meteors / hour, originating from Comet 1861 I Thatcher).
-Orionids (Orion constellation, during the month of October, the maximum occurs around October 21, between 10-20 meteors / hour, left by Halley's Comet).
-Geminids (constellation Gemini, the maximum is from December 13 to 14, 100-120 meteors / hour, created by the asteroid 3200 Phaeton).
-Draconids (constellation of the Dragon, they experience the maximum between October 8-9, more than 10 meteors / hour, the comet of origin is the Giacobinie-Zinner).
-Taurids (Taurus constellation, the maximum is expected around November 11 for the southern Taurids, coming from Comet Encke, and from November 13 to 14 for the northern Taurids).
Some rains such as the Perseids and Orionids can be seen in the southern skies, although a little lower on the horizon, requiring secluded places with clear skies..
The following rains can be admired high in the sky of the southern hemisphere, especially during the winter months of July, August and September:
-Eta Aquarids (Aquarius constellation, visible between April and May, maximum on May 5-6, with more than 20 meteors / hour, associated with Halley's Comet).
-Delta Aquarids, (Aquarius constellation, from the beginning of July to the end of August, maximum around July 29-30, more than 10 meteors / hour, associated with comet 96p Machholz 1).
-Alpha Capricorns (Capricorn constellation, have their maximum between July 27-28, of uncertain origin)
Observing meteor showers is a simple and very pleasant way to make astronomical observations, following these tips:
- Try to observe clear skies, away from trees and tall buildings.
- The sky should be dark, preferably with the Moon below the horizon. If it is the night of the full moon, it is preferable to wait for it to go down or try to observe the rain before the moon appears.
- Find places with the least amount of light pollution.
- After midnight more stars are seen, thanks to the fact that the Earth's rotation tilts us towards them, instead of waiting for them to come towards us from behind. Two or three hours before sunrise are the best times.
- The radiant must be at a good altitude above the horizon. The following section describes in detail how to determine this point..
- The best field of vision is obtained while lying on a reclining chair, a hammock or on mats and blankets on the floor. Wait a bit for your eyes to adapt well to the dark.
- Bring coats, pillows, food, drink, insect repellent and smartphone with sky map apps. There are excellent and free.
- Binoculars or telescopes are not necessary as they limit the field of view. The best thing is to walk the view all over the sky.
- When observing a shooting star, try to trace its path to locate the radiant and identify the constellation.
Meteor showers appear to come from a particular area of the sky thanks to a perspective effect. Meteors reach the atmosphere following parallel lines that appear to converge in a small area. To locate it, two coordinates are required:
- Right Ascension (α coordinate): angle measured from the point Aries in hours, minutes and seconds to the east, along the celestial equator. In figure 4, the corresponding arc is the orange segment on the celestial equator.
- Declination: vertical angle between the center of the observed object and the celestial equator, in figure 4 this angle corresponds to the vertical arc in orange.
Positive declination angles indicate objects above the celestial equator, while negative angles indicate objects below.
For example, the south celestial pole has a declination of -90 °, points on the celestial equator are at 0 °, and Polaris - the pole star - is at a declination of + 90 °..
In astronomy texts, words are used that, although they are commonly used when talking about meteor showers, have slightly different meanings. Such is the case of the terms "meteorite", "meteor" and "meteoroid":
Remnant of a comet or asteroid, orbiting the Sun and ranging in size from 100 microns to several tens of meters.
It is a meteoroid that has entered the atmosphere and disintegrated right there due to friction, but not before producing the light trail typical of shooting stars..
It is the meteoroid that did not completely disintegrate when passing through the atmosphere, so that one or more fragments manage to land. They can cause damage, such as that of the Russian town of Chelyabinsk (southern Urals) in 2013, or that of Tunguska (Siberia) at the beginning of the 20th century.
Known as fireballs, whose magnitude is comparable or smaller than that of the planet Venus, they are large and when falling they produce a noise like the explosion of a cannon or a hiss.
Conglomerate of rocks, ice and dust in an almost always elliptical orbit around the Sun. They are part of the Solar System, living on the outskirts, in the Kuiper belt and the Oort cloud.
Rocky object smaller than a planet and larger than a meteoroid, with a well-established orbit. Recently, both comets and asteroids have been classified in the same group, that of the "minor bodies of the Solar System".
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