What are Stars and Constellations and Life and Death of the Stars

Stars and Constellations

Constellations are apparent groupings of stars which ancient astronomers imagined to form figures of people, animals or objects . On a dark night, you can see between 1000 and 1500 stars, and each star belongs to some constellation. The difference between asterisms and constellations is basically that constellations are, in astronomy, a conventional grouping of stars, whose position in the night sky is apparently invariable. … Stars are celestial bodies that have their own light.


Stars are large spheres of plasma , held together by their own gravity . Stars emit light, heat and other types of radiation due to the nuclear fusion processes that occur in their interior, releasing large amounts of energy.

How are stars created?

Stars are formed by the condensation of gases that coalesce by gravitational attraction. The great nebulae, for example, are “nursery” of stars, since, in their interior, great molecular clouds give rise to new stars. When the gases responsible for star formation come closer together, their velocity increases, driven by local gravity, as well as their density and temperature.

During a period, which can take up to 10 million years, these protostars (stars in the initial stage of formation) are compacted by their own gravities until the pressure and temperature in their core are sufficient for the hydrogen atoms to fuse, producing helium nuclei. The stars that extract their energy from the fusion of hydrogen atoms are called main sequence stars, this type of star corresponds to about 90% of all stars in the Universe.

From the moment that stars become capable of performing thermonuclear fusions , their fuel is consumed, until the star evolves to its final stage of life. The possibilities are many: according to the mass of the star and its radius, it is possible to estimate what its future will be like. These stellar quantities, such as the mass and radius of stars, are commonly measured in terms of solar mass (M☉) and solar radius (R☉).

What are stars made of?

Most stars, whose masses range from 0.5M☉ (half the mass of the Sun) to 2.5M☉, are composed of helium and hydrogen, the most abundant elements in the Universe. That’s because these stars don’t have gravity or temperatures high enough to fuse heavier elements.

When stars are very massive: between 5M☉ and 10M☉ – like supergiants, elements heavier than helium are formed in their interior. The final stage of life for these stars is a supernova , a huge explosion that hurls all of its matter and energy into space, giving rise to other stars and planets.

Life and Death of the Stars

The “lifetime” of stars depends on their mass: the speed with which they consume their fuel is what tells how long the star maintains its brightness, the Sun, for example, consumes less than 0.01% of its mass, annually, increasing its temperature and luminosity. It is estimated that since the moment the Sun became a main sequence star, 4.6 billion years ago, its brightness has increased by more than 40%.

The main sequence stars, called dwarf stars, are the absolute majority of stars in the Universe, our Sun, for example, is a yellow dwarf, a main sequence star of “low temperature” when compared to the stars more hot, like blue dwarfs. Check out some of the evolutionary stages of stars according to their mass:

  • Very low mass stars: These stars, whose masses are up to half the solar mass, eventually cool down after consuming the hydrogen in their interior, theoretically becoming white dwarfs formed exclusively by helium, however, the calculated lifetime for this type of stars is larger than the universe itself, so existing stars will still become white dwarfs.
  • Low-mass stars: In their final stages of life, stars up to 2.5M☉ begin to form carbon and oxygen atoms in their core. With the decrease in their masses and the consequent decrease in their gravitational field, these stars become giants. During their expansion, these stars expel their outer layers, forming planetary nebulae.
  • Intermediate-mass stars: These stars have an evolution similar to low-mass stars, after their expansion, they leave behind only their core, giving rise to dwarf stars.
  • Massive stars: After having fused all their hydrogen, these stars expand, becoming supergiant stars, during this period, they begin to fuse heavy elements until their gravity cannot withstand the force of nuclear reactions, when this happens, these stars explode, launching its content through space at extremely high speeds

types of stars

There are different types of stars. That designation depends on two things: the spectral classification, which relates to the star’s temperature, and the star’s size and mass. The spectral classification is given in color. In order of increasing temperature, we have red, orange, yellow, yellow-white, white, blue-white and blue stars. Check out the image below about the evolution of stars:

This color definition concerns the peak frequency emitted by the star and that related to the blackbody emission temperature . As stars produce almost all frequencies of radiation simultaneously, to the human eye they all appear whitish to the naked eye.

Check out some of the most important types of stars that exist:

  • Blue stars : These are extremely hot stars, their surface temperature can reach 30,000 K, they are very “new” stars compared to other types of stars. Most of these stars were created less than 40 million years ago.
  • Yellow dwarfs : Just like the Sun, these stars are very old, having existed for billions of years. The future of these stars is to become a red giant.
  • Red dwarfs : They are the most common stars, they represent about 73% of the stars in the Universe. Their brightness is weak, they are low-mass stars.
  • Blue giants : These are stars with temperatures greater than 10,000 K, very massive, with up to 250 times the mass of the Sun.
  • Blue supergiants : They are rare, extremely hot and bright, they can have up to a thousand times the mass of the Sun.
  • White dwarfs : These stars are formed by the cores of other stars that have ejected their outer layers, these stars no longer produce nuclear fusions and commonly rotate around their axes with very high speeds.
  • Neutron stars : These are stars that have been so compressed that all of their protons and electrons have been ejected due to electrical repulsion. They are very small, between 5 and 15 km in radius and their temperatures exceed hundreds of thousands of degrees Celsius.

In some cases, supermassive stars, with masses greater than three solar masses, can collapse, giving rise to black holes. Black holes do not allow light to escape from their interior because of their enormous gravity.

However, around black holes it is possible to observe accretion disks: they are the gases of other stars that orbit them. When accelerated towards the event horizon, the region of black holes from which nothing escapes, the gases are heated, starting to emit different frequencies of electromagnetic waves .

What is the number of stars in the sky?

Although it seems simple, this is an extremely difficult question to answer, simply because it is not possible to count such a large number directly. It is estimated, however, that there are at least 10 10 galaxies in the observable Universe, which may contain a few billion stars.

In our galaxy, the Milky Way , and also in our closest neighbor, the Andromeda Galaxy, for example, there are at least 100 billion stars, as a result, astronomers’ estimates indicate that there must be at least 10 21 stars in the whole Universe.

Despite the enormous number of stars, a tiny part of them is visible from Earth with the naked eye. From here, without the aid of any optical instrument, it is only possible to see about 10,000 stars.

star names

Currently, there are about 330 official and proper names for stars. Check out some of these names, as well as some characteristics of each of these stars:

  • Canis Majoris: The star VY Canis Majoris (scientific nomenclature) is one of the largest known stars, this hypergiant has about 1420 solar radii.
  • Sirius: Sirius is a binary star, the brightest in the sky, located 8.6 light years from Earth.
  • Canopus : It is the second brightest star in the sky, it is at a distance of 310 light years from Earth.
  • Aldebaran: It is a red giant, the brightest in the constellation Taurus, located 65 light years from Earth.
  • Rigel : It is the brightest star in the constellation of Orion and the seventh brightest star in the sky.
  • Betelgeuse : It is the twelfth brightest star in the sky and the brightest star in the constellation of Orion.
  • Antares : It is a supergiant star, with a radius greater than 822 solar rays, it is located 600 light years from Earth.
  • Canopus : It is a red supergiant, the brightest star in the constellation of Carina.

What is a constellation?

In astronomy , a constellation is a grouping of different stars in a portion of the celestial vault, which apparently evokes a certain shape or silhouette, from which a name is given. These are completely arbitrary associations, which often respond to figures and symbols from culture , and therefore vary from one society to another.

The first constellations were identified in ancient times, when the cousin cultures of the Euphrates Valley dedicated themselves to observing the sky more carefully, and recognized the recurring presence of the same stars in the same regions of the firmament.

The different peoples of Antiquity gave this fact their own pseudo-religious explanations, commonly linked to their founding stories. Thus, for example, the ancient Greeks saw in them their heroes and their gods , while the ancient Chinese distinguished a group of celestial houses and mansions, and the Incas a group of sacred animals.

In the case of Western astronomy, the constellations established by the Greco-Roman ancestors are considered to exist, mainly those from Greek mythology.

In fact, the word constellation is an inheritance from the Latin constellatus , made up of the voices com- (“together” or “union”) and stella (“star”); and this language is also used to name the constellations and the stars that constitute them, for which the Latin declensions of the nominative and possessive genitive are used. In this way, the constellation of the centaur is called centaurus , but the main star of the set is called alpha centauri , that is, “the first of the centaur”.

See also: Celestial bodies

How many constellations are there?

According to the International Astronomical Union, 88 constellations are formally recognized . Of these, 47 were identified and named by the Greek astronomer and mathematician Claudius Ptolemy (c.100 – c.170 AD), who in 150 AD. C. a celestial catalog with more than 1000 stars grouped in their respective constellations; and 41 were added later, throughout the 16th and 18th centuries, largely thanks to the guidance they offered to navigators and explorers.

The number of total constellations is fixed, but the observable constellations vary depending on the hemisphere of the planet from which it is observed. Thus, the northern hemisphere contains 36 constellations and the southern hemisphere contains 52.

What are the main constellations?

Some of the best-known constellations in the firmament are the following:

Constellations of the Northern Hemisphere :

  • Andromeda constellation . She represents the princess of the same name, daughter of Cepheus and Cassiopeia, who according to Greek mythology was chained to a rock to be devoured by Ceto, a sea monster, but later rescued by Perseus. This constellation, one of the largest known, has 152 stars, of which the brightest is Alpheratz ( alpha andromedae ).
  • Orion constellation . It represents the greatest hunter of Ancient Greece, visible as a warrior holding his weapon and his shield. Said hunter was the protagonist of numerous Greek myths , in some of which he was the pursuer of the Pleiades, the daughters of the Titan Atlas. This constellation is visible from both the northern and southern hemispheres, and is recognizable by the three nearby stars that make up its belt. In total, Orion consists of 204 stars, of which Rigel ( beta orionis ) is the main and brightest.
  • Cassiopeia constellation . It represents Cassiopeia, wife of the king of Ethiopia according to Greek mythology, whose beauty and vanity caused the wrath of the god Poseidon, who sent a sea monster to lash the shores of his kingdom. This constellation consists of 157 stars, of which the brightest is Tsih ( gamma cassiopeiae ).
  • Perseus constellation . It depicts the classical Greek hero of the same name, responsible for beheading Medusa and rescuing Andromeda, his future wife, from the jaws of a sea monster. The famous Perseid meteor shower occurs inside it, and it consists of a total of 158 stars, of which Mirfak ( alpha persei ) is the brightest.
  • Triangle constellation . It represents, as its name indicates, a triangle, in which the ancient Greeks saw the letter delta (𝛥). It is a minor constellation, at least in Greek mythology, which should not be confused with the constellation Triangulum australe , from the southern hemisphere. In this constellation there are only 25 stars, of which Deltotum ( beta trianguli ) is the main one.

Constellations of the southern hemisphere :

  • Crux constellation . It represents, as its name indicates, a cross, but as it belongs to the southern hemisphere, it is popularly known as the “Southern Cross”. It is one of the most useful constellations for navigation, since its main axis always points towards the South Pole. This constellation has 49 stars, of which Acrux ( alpha crucis ) is the brightest.
  • Constellation of Canis Major . In Greek mythology, it represents the hunter’s dog Orion, which is why it seems in the sky to always be following the path of his owner. This constellation has 147 stars, of which Sirius ( alpha canis majoris ) is the brightest (in fact, it is the brightest in the sky).
  • Hydra constellation . It represents the mythological monster of the hydra, a kind of multi-headed reptile, which grew two new heads every time the hero decapitated one with his sword. It is one of the largest modern constellations, which extends on both sides of the Earth’s equator, that is, both in the south and in the north. It consists of 238 stars, of which the brightest is Alfard ( alpha hydrae ).
  • Constellation of the South Crown . It represents the laurel wreath that belonged to the wise Chiron, the centaur who was the teacher of numerous Greek heroes in mythology. It is a small constellation, very close to Sagittarius, consisting of 46 stars, of which Beta coronae australis is the brightest and largest.

The constellations of the zodiac

Among all the constellations, there are 12 that occupy a particular place in the celestial vault: an imaginary band 18 degrees wide, centered on the ecliptic (that is, on the apparent path of the sun along the terrestrial sky) and divided into twelve sectors of 30 degrees longitude of the ecliptic, each of which corresponds to a unique sign.

This band is known as the zodiac (from the Greek zodion , “small animal image”) since the Greeks identified the constellations located in this strip of the sky with different figures and animalsThese twelve constellations are those that determine the astral signs of people , depending on which of them (or their surrounding spaces, known as “houses”) the Sun is when a person is born.

The constellations of the zodiac are the following:

  • Aries (from Latin aries ). It represents the head and horns of a ram, corresponding in Greek mythology to the ram that saved the lives of the Argonauts Frixio and Hele, who in return sacrificed it to the god Ares, who promoted it to the firmament. Later his skin would be the golden fleece. This constellation is made up of 86 stars, of which Hemal ( alpha arietis ) is the brightest of all.
  • Taurus (from Latin taurus ) . It represents the Bull of Crete and at the same time the form that Zeus adopted to kidnap the Phoenician princess Europa and take her to Crete so that she could be her lover. This constellation is made up of 223 stars, of which the brightest is Aldebaran ( alpha tauri ).
  • Gemini (from Latin gemini ) . She represents the mythological twins Castor and Pollux, known as the Dioscuri and brothers of the famous Helen of Troy. This constellation consists of 119 stars, and the two brightest are precisely Pollux ( beta geminorum ) and Castor ( alpha geminorum ).
  • Cancer (from the Latin cancer ) . It represents a crab, an animal present in numerous ancient mythological traditions. It can be found in the Egyptian temple to Hathor, in Dendera; but also in the Greek account of the labors of Hercules, in which the goddess Hera sends a crab to sabotage the hero’s efforts to kill the Lernaean hydra. This constellation consists of 104 stars, of which the brightest is Tarf ( beta cancri ).
  • Leo (from Latin leo ) . He represents a lion, an animal of symbolic and mythological importance in a large number of ancient peoples, especially the Mesopotamians. In the first century AD. C. this constellation was reinterpreted to allude to the Nemean Lion, a creature defeated by Hercules in Greek mythology. This constellation consists of 300 stars, and the brightest is Regulus ( alpha leonis ).
  • Virgo (from Latin virgo ) . She represents Astrea, a virginal titan from Greek mythology, daughter of Zeus and Themis, representative of earthly justice (and therefore called Iustitia by the Romans) and the last immortal to live among human beings. This constellation consists of 169 stars, of which Spike ( alpha virginis ) is the brightest.
  • Pound (from Latin pound ) . It represents a scale, an ancestral symbol of justice and equity, attributed in Greek mythology to the Titaness Astrea, who embodied earthly justice. This constellation, quite inconspicuous compared to the rest of the zodiac, consists of just 83 stars, of which Zubeneschamali ( beta librae ) is the brightest.
  • Scorpio (from Latin scorpio ) . It represents a scorpion, an animal with a wide presence in the imaginaries of Mesopotamian, Egyptian and Greek antiquity. In Egyptian culture, it is part of the myth of the hunter Orion, who swore to the gods that he would kill every last animal on planet Earth and received a scorpion as punishment, which chased him around the world until it killed him with its sting. This is how the Greeks explained that the constellation of Scorpio emerges in the celestial vault when that of Orion hides. The constellation of Scorpio consists of 167 stars, and among them the brightest is Antares ( alpha scorpii ).
  • Sagittarius (from Latin sagittarius ) . It depicts a centaur holding a bow and arrow, and his name means “the archer” in Latin. This centaur corresponds in Greek mythology to Chiron, the wise teacher of numerous Greek heroes, whom Hercules accidentally killed with an arrow poisoned with the poison of the hydra. This constellation has 194 stars, of which Kaus Australis ( epsilon sagittarii ) is the brightest.
  • Capricorn (from Latin capricornius ) . It represents a billy goat or goat, associated in the 1st century AD. C. with the Aegipán, a hybrid creature of goat and fish, which the ancient Greeks considered related to the rural god Pan. His ascent to the firmament, according to Greek mythology, was due to the discovery of the musical conch, an instrument with which he helped scare away the titans during their war against the olympian gods. This constellation has only 81 stars, of which Deneb Algedi ( delta capricorni ) is the brightest.
  • Aquarius (from Latin aquarius ) . It represents a human figure, sometimes male and sometimes female, holding a jug of water. In some mythological traditions it is the god of the storm, of the rain or the personification of the universal flood, whose role is to purify the Earth; but in Greek mythology it is associated with Ganymede, the cupbearer of the Olympic gods. This constellation consists of 172 stars, of which the brightest is Sadalsuud ( beta aquarii ).
  • Pisces (from Latin pisces ) . It represents a couple of fish, creatures universally present in the mythological traditions of the world, but which in the Greco-Roman tradition alludes (according to Eratosthenes in 276 BC) to the great fish that saved Derceto, one of Aphrodite’s daughters, from drowning in a lake into which he had fallen. According to other versions, it would be about Venus and Cupid, when mother and son fled from the monster Typhon, turned into fish, but tied with a rope so as not to get lost in the immensity of the sea. This constellation has 150 stars, of which Kullat Nunu ( nu piscium ) is the brightest.

family constellations

Family constellations are known as a pseudo-therapeutic method that proposes the existence of recognizable patterns in people ‘s families , unconsciously perceived and memorized, to later be reproduced in intimate relationships in adult life.

This theory, proposed by various German psychiatrists in the 20th century but harshly criticized from a scientific point of view, is distantly related to psychoanalysis, since it proposes the re-enactment of family ties as a way to identify harmful affective patterns learned. in childhood .

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