COMET

The comets (of the Greek kometes that it means «star with hair») are minor bodies, with sizes that go from a few meters up to some kilometers of diameter, composed of ice and silicate. It is a question basically of big «balls of dirty ice». His orbits, normally very elongated, lead them to spending most of the time much removed from the Sun, in cold regions of the Solar system. But when they approach the star king, they warm up and the ice (principally of water) is sublimated and goes on from the solid state to gas. This gas, which escapes of the solid nucleus of the comet, drags with it dust particles and «comma« forms extensive clouds about the comet called «hair« o. The materials that form the hair are dragged in the opposite direction to the Sun by the solar wind and they give place to the "tails" cometarias. After his step close to the Sun, the particles of the hair and of the tail of a comet remain distributed along his orbit and when the Earth, in his draft about the Sun, crosses one of these orbits, the called stars rains take place. This phenomenon takes place when minuscule particles of dust proceeding from the comet enter the terrestrial ambience at big speed and disintegrate for friction, producing the luminous track that we call a meteor or shooting star.
At least 3 types of comets exist: those of «short period» or of the «family of Jupiter», objects with an orbital period minor than 20 years and orbits scarcely inclined with regard to the ecliptic (plane of the terrestrial orbit); those of type «Halley«, with more elongated orbits, periods of tens years and inclinations that can be very big; and those of «long period», with alargadísimas orbits and periods that go from thousands of years up to objects that have happened for the closeness of the Sun the only time from the origins of the Solar system.

The big comet of 1997, the Hale-Bopp photographed along with the galaxy of Andrómeda and Perseus's double heap. Credits: Vicente Aupí (Observatory of Torremocha del Jiloca).

Glossary: "100 basic concepts of Astronomy”

The lads and his vision of the science

Sometimes I wonder how the lads see us, the scientists, what they think on what we do, in what universe they believe that we unroll ourselves. I refer to those that are still in primary, in the first formation stages, when everything is new, fascinatingly. When one is truly receptive and the future of a child can change completely for a few experiences.

Today I have received a message of my nephews César and David, with a few drawings, in which I can see straight what they think of the Astronomy and the image that they have on me, like investigator. So I share it with you. Small details like that do that the investigation and the publication is worth while.

Watch Southland S02E03 U-Boat free

EXPANSION OF THE UNIVERSE

It has been observed that the distances between the big structures of the universe (the heaps and galaxies superheaps) increase in a progressive way. This fact observacional is named an expansion of the universe and it was discovered by Edwin Powell Hubble and Milton Lasell Humason in 1929. If two heaps of any galaxies take, the distance between them grows incessantly, and does it not because the galaxies or the heaps are displeased, but because there grows the space that comes up between them. Moreover, the more distant between themselves are the considered heaps, the faster is the increase of the distance. The intensity of the expansion of the universe for any moment of his history is valued by means of the Hubble parameter, H. The current value of the parameter of Hubble receives the name of constant of Hubble and is symbolized as H0. The expansion of the universe does not affect to tied systems gravitatoriamente, that is to say, the process does not alter the distances between the atoms of our bodies, between the Earth and the Sun or even between the stars of the Galaxy or between galaxies belonging to the same heap. The remarks indicate that the expansion of the universe is hastening increasingly, for motives that are still not clear.

Glossary: "100 basic concepts of Astronomy”

Streaming Lost S06E08 Recon now

DISPLACEMENT TO THE RED ONE

The electromagnetic waves, like for example the light, are characterized by his wavelength, that is to say, for the distance that comes up between two consecutive undulatory combs. An any wave, be or not electromagnetic, it can be expressed by a certain wavelength but then it is possible to see affected by multitude of processes that do that the recipient receives it with a different wavelength.
In case of the sound, when it changes the wavelength there falters the tone perceived (sharp or serious character). In case of the light, the changes of wavelength bear modifications in the color.
The displacement to the red one is only a change in the wavelength of the electromagnetic radiation. An electromagnetic wave expressed with a certain wavelength (a certain color) is received by a wavelength (color) different. When this alteration implies a reddening of the tone of the light or, in general, a lengthening of the wavelength, one speaks about displacement towards the red one. Although the displacement towards the red one should be the most popular, it is necessary to insist that also it is possible that there takes place a reduction of the wavelengths of the radiation: in this case one speaks about displacement to the blue.
In case of the electromagnetic radiation in general, and much in particular if it is a question of the light, this change of wavelength can owe to three different physical processes: to which the issuer and the recipient move away between themselves (effect Doppler), to which the issuer is submitted to a gravitational field more intense than the recipient (displacement to the red gravitational one) or to the expansion of the universe (displacement to the red cosmological one). When issuing and receiving they approach, when the recipient experiences a more intense gravitational field or when the universe contracts, then the opposite effect, the displacement takes place to the blue. The displacement to the red one is represented by the letter z. The variable z adopts positive values when it is a question of a displacement to the red one and negatives if it is a question of a displacement to the blue.
Since it has been indicated, the displacement to the red one (or) can have three well differentiated physical causes to the blue. But there is one of them who stands out for his importance and for the frequency with which it appears in physical contexts, and especially in astronomical problems: the effect Doppler.
The change is known as an effect Doppler in the length of a wave as a result of the movement of the issuer with regard to the recipient. We observe this effect numerous times in the daily life. When a car us approaches at big speed, we perceive that the sound of the engine (a wave, after all) is sharper than when it moves away from us. This perception owes to the fact of which when the car approaches, the expressed sonorous waves seem to join and diminishes his length, while the opposite effect takes place when the car removes, situation in which the waves seem to separate, what does that his length increases.
This effect is very important in astrophysics, where he acquires relevancy applied to the electromagnetic waves, especially to the case of the light. When an object that expresses light, like a star or a galaxy, approaches us (or we to the object), we see his compressed light waves, with minor wavelength than the correspondent to the emission: the color moves towards the blue. If the issuing body moves away from us (or we of the issuing body), then we see that his light moves the red one, his waves get longer. The effect returns more intense major all that is the relative speed between the issuer and the recipient, which allows to use the effect Doppler to calculate the speed of the stars with regard to us.
This effect receives his name of the Austrian physicist Christian Doppler, and it was key in the discovery of the expansion of the universe for Edwin Hubble. Nevertheless, it is necessary to clarify that the displacements to the red one of which so much it is a question in cosmology do not owe to the effect Doppler, but to an independent effect, that of the displacement to the red cosmological one related to the expansion of the universe, and not with the displacement of the galaxies in strict sense in the bosom of the space.

Glossary: "100 basic concepts of Astronomy”

ASTEROIDS

There are minor bodies of the Solar system, for the most part consisted of silicates and metals. Most of them are small, of some meters until tens o'clock of kilometers, and of very irregular forms. Few ones reach several hundreds or up to thousand kilometers in diameter. This is the case of Ceres, the first asteroid, discovered in 1801 for Giusseppe Piazzi.

Asteroid (433) Eros. Reconstruction of the images taken the spatial probe NEAR-Shoemaker in February, 2000. Credits: NEAR Project, NLR, JHUAPL, Goddard SVS, NASA.

Almost all the asteroids are in the region between Mars and Jupiter known like principal belt. This has been the first bodies ring minor known (the second one was the transneptuniano). In the first stages of the evolution of the Solar system million bodies formed of up to some hundreds of km of diameter, from the aggregation of the silicates and metals that were abounding in the region of the terrestrial planets. While those who formed in the interior region Mars joined giving place to the terrestrial planets, those that formed a little further on of Mars could not join to form another planet. The closeness of Jupiter modified his orbits in such a way that, on having hit, between themselves they were doing it at speeds so high that, instead of joining to form a major object (as it happened to him to the most interior objects), more children were breaking the sliced objects.
Not all the asteroids are in the principal belt; some of them have been ejected of this one due to gravitational perturbations and mutual collisions. The orbits of some of these ejected asteroids approach to the Earth and all those ones whose minimal distance to the Sun is minor than 1,3 times the distance of the Earth are considered to be Nearby Asteroids (or NEA, of English near earth asteroids). Some NEA are potentially dangerous since they can collide with the Earth.

Glossary: "100 basic concepts of Astronomy”

METEORITE

The small particles (up to approximately ten meters) that orbit about the Sun receive the name of meteoroids. These particles are associated with the comets and asteroids, but also they can have been started of satellites or planets after violent shocks with other bodies.

A fragment of the meteorite of Port photographed Lápice in situ for Alejandro Sánchez. The copy is exhibited at present in the National museum of Natural sciences. Credits: Alejandro Sánchez (Complutense University of Madrid).

When one of these extraterrestrial particles penetrates in the terrestrial ambience, it warms up for rubbing with the air, becomes incandescent and meteor or shooting star gives place to a so called light twinkle. There are called racing cars those meteors which luminosity is superior to that of the planet Venus.
Sometimes, the meteoroid responsible for a shooting star or for a racing car not volatiliza completely in the process and it survives point or fragmented up to coming to the soil. To this fragment of rock originated from the space we will call it a meteorite. The observation of the racing cars allows to reconstruct sometimes the trajectories and deduce the area of the surface where they have fallen down, what it helps to the meteorites recovery for his later study. The meteorites can be rocky, metallic, or a miscellany of both. His study informs us about the composition and history of the bodies of the solar system. More than 31 000 meteorites have recovered; their fall of more than 1000 was observed by some witness.

Glossary: "100 basic concepts of Astronomy”

PLANET

The International Astronomical Union, in his plenary assembly celebrated in Prague in August, 2006, established a definition of the term planet, at least as for the Solar system. This way, a planet is a celestial body that: (a) it orbits about the Sun; (b) it possesses enough mass as so that its own gravity dominates the present forces like rigid body, what implies a form approximately rounded determined by the balance hidrostático; (c) is the clearly domineering object in his neighborhood, having cleaned his orbit of bodies similar to him. According to this definition, Pluto stops being a planet, to happen to be the prototype of a new type of objects: the dwarf planets. Inside the category of dwarf planets are Pluto, Ceres and Eris. Therefore, the Solar system remains with eight planets: Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus and Neptune. In our solar system there are two types of planets, gaseous and rocky, and of two types planets have been discovered orbiting other stars different from the Sun.

Saturn observed by the mission Cassini-Hyugens, with the secret Sun for the eclipse due to the disc of the planet. Although a certain material quantity exists about this gaseous giant in the shape of numerous satellites and multiple rings, Saturn dominates the whole set. Credits: Cassini Imaging Team, SSI, JPL, THAT ONE, NASA.

The gaseous planets are those constituted principally by gases, in particular hydrogen and helium. In our Solar system they belong to this category Jupiter, Saturn, Uranus and Neptune, although in the above mentioned the ice is a substantial component in his composition. The gaseous planets, depending on his formation mechanisms, do not have why to possess a rocky solid nucleus, but they can consist of a gas continuous one gradually denser that they acquire finally the properties of a fluid when it is to high pressure. In case of Jupiter and Saturn, the gaseous hydrogen in the molecular state passes the state known as «metallic hydrogen» with a few particular properties. Immense most of the extrasolar planets discovered up to the date are gaseous planets in consequence, at least partly, to that the current detection methods discriminate better against planets of major mass.
The rocky planets, also been called telluric, are the planets formed principally by silicates, in which the ambience is secondary and is influenced by the geologic activity and, in case of the Earth, by the biological activity. In the Solar system four rocky planets exist: Mercury, Venus, the Earth and Mars.

Glossary: "100 basic concepts of Astronomy”

EXOPLANETA OR EXTRASOLAR PLANET

The International Astronomical Union (UAI) defined in a provisional way the exoplaneta concept in the year 2003. According to the same one, the planets out of the Solar system must orbit about a star or remnant of star (white dwarf or neutrons star) and have a mass lower than 14 masses of Jupiter. Due to his limited mass, temperatures and thickness do not reach it in his interiors sufficiently high as to fuse deuterium, an isotope of the hydrogen composed by a proton and a neutron, or any other chemical element. Therefore, they do not produce energy from this type of source.

The system exoplanetario of the star HR8799, composed by at least three exoplanetas. The image was obtained by the telescope Keck and special skills that allow to heighten the contrast and eliminate almost the whole sheen of the central star. His planets have masses between 7 and 10 times that of Jupiter and orbit at big distance of the star (15, 40 and 70 astronomical units). Credits: Christian Marois, Bruce Macintosh, Keck Observatory.

According to the same resolution of the UAI, the substellar objects, with masses superior to the previous ones, but that do not fuse hydrogen, they must be named brown dwarfs. On the other hand, the isolated objects of planetary mass, with mass below the limit of 14 masses of Jupiter, must be named brown subdwarfs or any other name that is appropriate, except planet.
Of course, these definitions might modify according to our knowledge advance. Some investigators think that the brown sub-dwarf expression is not very guessed right, and that other terms would be more suitable as IPMOs, planemos, oriones, or xebarcos.

Glossary: "100 basic concepts of Astronomy”

DWARF PLANET

A dwarf planet is a celestial body that fulfills the following conditions: (a) it orbits about the Sun; (b) it possesses enough mass as so that its own gravity dominates the present forces like rigid body, what implies a form approximately rounded determined by the balance hidrostático; (c) it has not cleaned his orbit of other objects; (d) is not a satellite of a planet. This way, Pluto (overdraft in the year 1930 for C. Tombaugh), Ceres (the first asteroid, found in the year 1801 for G. Piazzi) and Eris (or Éride, identified in 2005 for M. Brown) happens to be dwarf planets. In particular, Pluto loses his status as planet because it does not fulfill one of the characteristics that yes present eight planets of the Solar system: it is not the domineering object in his region of the space or, said otherwise, it has not managed to sweep his orbit, but he shares the area with multitude of other objects of the same type, the bodies that shape the objects belt transneptunianos.

Pluto has turned into the prototype of the plutoides, which would consist of those dwarf planets (therefore, from similar characteristics to those of Pluto) located beyond the orbit of the planet Neptune (which distance is approximately 30 times the one that separates the Earth of the Sun, or 30 astronomical units). This way, the plutoides are dwarf planets transneptunianos. Therefore, Ceres placed in the belt of asteroids (approximately 2.8 au), would not enter inside this category.
At present alone Pluto, Eris, Makemake and Haumea are considered officially plutoides. In principle, any object transneptuniano that has an approximate diameter of approximately 800 km is a candidate for being considered to be a plutoide and a name will be assigned to him as if it was. One hopes that more plutoides should receive names as the science progresses and new discoveries should be realized.

Ceres, a dwarf planet, and Vesta, an asteroid of big size. Both are between the orbits of Mars and Jupiter, in the Belt of Asteroids, where there is located multitude of objects of different masses and forms. Credits: Image of Ceres of J. Parker (NASA, THAT ONE), Vesta's image of L. McFadden (NASA, THAT ONE).

Glossary: "100 basic concepts of Astronomy”