What is Shower of stars?
A shower of stars due to the effect of light produced when particles from the Solar System affect 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 the heating by friction between them and the particle.
The sight of these fleeting objects is one of the most beautiful and easy to admire celestial spectacles; therefore, a frequent question for all fans is where do they come from?
How do Shower of stars form?
As with 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 subject captured since then.
In the vicinity of the Solar System, beyond Pluto’s limits, inhabit objects such as comets and asteroids.
When one of them ventures close enough to the Sun, often a periodic comet, the gravitational interaction is so intense that some of its mass is lost, leaving a trail of matter in the orbit.
What remains are particles whose size varies from microscopic grains to agglomerates of matter of good size – about 100 km for example – called meteoroids . Each time Earth approaches and intercepts the comet’s orbit, the probability of finding them increases.
Meteoroids penetrate the Earth’s atmosphere at high speed, continually colliding with the atoms and molecules they encounter in their path and producing some of their kinetic energy. Another part results in the heating of the same meteoroid.
At approximately 100 km in height, the ionization of the atmosphere leaves a brief trail of light that we recognize as a “shooting star” or “meteor”. Heating almost always leads to the complete evaporation of the body, but if it is too massive, one or more fragments – lightning bolts or fireballs – manage to impact the ground.
Comet debris forms the origin of nearly all known showers. An exception is the Geminids, a shower left by the fragmentation of asteroid 3200 Phaeton.
Main Shower of stars and their characteristics
Shooting stars can be seen sporadically on any given night, as the space through which Earth’s orbit passes is full of particles, so the trajectory can be virtually any.
The most striking stellar showers occur during the periods of the year when the Earth crosses the orbits of fractured comets, noting that a large number of them follow a path that converges at a specific point in the sky: the radiant . This is a perspective effect.
In addition to radiation, stellar showers are characterized by the rate of observable meteorites per hour or the zenith hourly rate (THZ), which can 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 rainfall, called the population index .
Among the showers with a well-established trajectory are the Perseids , so named because their radiation is in the constellation Perseus, visible in early August.
Another very attractive shower is the Leonids, observable in November and radiant in Leo. In total, there are about 50 clusters named by the constellation where the radiant is or by the brightest and closest star.
The biggest showers are those with a high meteor count/hour, and year after year the night sky crosses, having appeared regularly for hundreds of years.
Below is a list with the estimated date of appearance and, later, a guide to better appreciate them.
The showers of the main stars and when they are observed
The main showers last for a few days or weeks, as the Earth progresses, while the maximum meteorite / hour occurs in a specific day or at most two.
Although it is an arbitrary limit, it is considered a heavy rain 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, like the Leonids every 33 years, reaching the category of stellar storms, when the rate is 1000 or more meteors / hour.
Most star showers are well liked in both hemispheres, although according to the radiant some look better on one or the other.
Star showers with the best visibility in the Northern Hemisphere
-Perseids (Perseus constellation, between July 16 and August 24, maximum from August 11 to 13, between 50 and 100 meteors / hour, originated by the comet Swift-Tuttle).
-Leonidas (constellation of Leo, from November 15 to 21, maximum from November 17 to 18, its origin is the comet Tempel-Tuttle, variable number of meteors per hour, usually between 10 and 15. In 1833, 1866 and 1966 there were at most thousands of meteors per minute).
-Cuaadrántidas (Boyero constellation, from the end of December to the first week of January, maximum from January 3 to 4, more than 100 meteors / hour, origin uncertain)
-Lyrids (constellation Lyra, moderate rain visible from 16 to 25 April, 10-20 meteors / hour, whose origin is the comet 1861 I Thatcher).
-Orionidas (Orion constellation, during the month of October, the maximum occurs around October 21, between 10 to 20 meteors / hour, left by Halley’s comet).
-Geminids (Gemini constellation, maximum is December 13-14, 100-120 meteors / hour, created by asteroid 3200 Phaeton).
-Dracónidas (constellation of the dragon, experience the maximum between 8 and 9 October, more than 10 meteors / hour, the comet of origin is Giacobinie-Zinner).
-Taurids (constellation of Taurus, the maximum is expected around November 11 for the southern Taurids, coming from the comet Encke, and from November 13 to 14 for the northern Taurids).
Showers with better visibility in the southern hemisphere
Some showers, such as the Perseids and Orionids, can be seen in southern skies, although slightly lower on the horizon, requiring remote locations with clear skies.
The following showers can be admired in the sky of the southern hemisphere, especially during the winter months of July, August and September:
– Eta Acuáridas (constellation of Aquarius, visible between April and May, maximum from 5 to 6 May, with more than 20 meteors / hour, associated with Halley’s comet).
– Delta Acuáridas , (Aquarius constellation, from the beginning of July to the end of August, maximum between 29 and 30 July, more than 10 meteors / hour, associated with comet 96p Machholz 1).
– Alpha Capricornidas (constellation of Capricorn, has its maximum between July 27th and 28th, of uncertain origin)
How to properly observe the Shower of stars
Watching star showers is a simple and very enjoyable way to make astronomical observations, following these tips:
– Try to observe the clear sky, away from trees and tall buildings.
– The sky should be dark, preferably with the moon on the horizon. If it’s a full moon night, it’s preferable to wait for it to fall or try to observe the rain before the moon appears.
– Look for 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 catch up with us from behind. Two or three hours before dawn 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 view is obtained lying down in a reclining chair, in a hammock or on rugs and blankets on the floor. It is advisable to wait a little for the view to adapt well to the darkness.
– Bring coats, pillows, food, drinks, insect repellent and smartphones with sky map apps. There are excellent and free ones.
– Binoculars or telescopes are not necessary as they limit the field of view. It’s better to look around the sky.
– When observing a shooting star, try to trace its path to locate the radiant and identify the constellation.
Placing the Radiant of an Object in the Sky
Star showers appear to come from a specific area of the sky, thanks to a perspective effect. Meteors strike the next atmosphere parallel lines that seem to converge in a small area. To locate it, two coordinates are needed:
– Right Ascension (α coordinate): angle measured from the point of 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 -90° decline, points on the celestial equator are at 0°, and Polaris – the pole star – is on a +90° decline.
glossary of terms
In astronomy texts, words that are commonly used when talking about star showers are used, they have slightly different meanings. This is the case of the terms “meteorite”, “meteor” and “meteoroid”:
Remnant of a comet or asteroid, which orbits around the Sun and whose size varies between 100 micrometers and several tens of meters.
It is a meteoroid that entered the atmosphere and disintegrated there through friction, but not before producing the luminous trail of shooting stars.
It is the meteoroid that does not completely disintegrate when passing through the atmosphere, so that one or more fragments manage to land. They can cause damage, like that of the Russian city 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 to or less than that of the planet Venus, they are large and, when they fall, produce a noise like a cannon blast or a hiss.
Conglomeration of rocks, ice, and dust often in an elliptical orbit around the Sun. They are part of the Solar System, living in the suburbs, in the Kuiper belt and in the Oort cloud.
Rocky object smaller than a planet and larger than a meteoroid, with a well-established orbit. Recently, both comets and asteroids were classified in the same group, the “smallest bodies of the Solar System”.