Par amely1 le 14 Octobre 2006 à 20:59WHAT IS COSMIC HISSSSS......???
This subject touch a part of my work, it is about the cosmic hiss, or called "cosmic microwaves background radiation (CMB), wich is permanent radfiation comming from the milkie way and the big bang.
The first sound of radiation was detected bye karl Jansky ( see the photo) who discover on his huge radio in the early 30's. Its a sound making a "hissssss" . That's why it is called "cosmic hiss", and actually we can detect the radiation coming from the big bang when we are surching a radio frequences, and we ear waves or also when we search a channel on TV, and we only see the TV snow...
Jansky life by "wikipedia":
Jansky was born in Norman, Oklahoma, to a Czech-American family. He was named after Dr. Karl Guthe, who had been an important mentor to Karl's father, Cyril M. Jansky. C. M. Jansky was an engineer with a strong interest in physics, a trait passed on to his sons. Karl's brother Cyril Jansky Jr., who was ten years older, helped build some of the earliest radio transmitters in the country, including 9XM in Wisconsin (now WHA of Wisconsin Public Radio) and 9XI in Minnesota (now KUOM).
Education and engineering
Jansky attended college at the University of Wisconsin where he received his BS in physics in 1927. In 1928 he joined the Bell Telephone Laboratories site in Holmdel, New Jersey. Bell Labs wanted to investigate atmospheric and ionospheric properties using "short waves" (wavelengths of about 10-20 meters) for use in transatlantic radio telephone service. As a radio engineer, Jansky was assigned the job of investigating sources of static that might interfere with radio voice transmissions.
Jansky built an antenna designed to receive radio waves at a frequency of 20.5 MHz (wavelength about 14.6 meters). It was mounted on a turntable that allowed it to rotate in any direction, earning it the name "Jansky's merry-go-round". It had a diameter of approximately 100 ft. and stood 20 ft. tall. By rotating the antenna on a set of four Ford Model-T tires, the direction of a received signal could be pinpointed. A small shed to the side of the antenna housed an analog pen-and-paper recording system.
After recording signals from all directions for several months, Jansky eventually categorized them into three types of static: nearby thunderstorms, distant thunderstorms, and a faint steady hiss of unknown origin. He spent over a year investigating the source of the third type of static. The location of maximum intensity rose and fell once a day, leading Jansky to initially surmise that he was detecting radiation from the Sun. After a few months of following the signal, however, the brightest point moved away from the position of the Sun. Jansky also determined that the signal repeated on a cycle of 23 hours and 56 minutes. This four-minute lag is a typical astronomical characteristic of any "fixed" object located far from our solar system (see sidereal day). By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way and was strongest in the direction of the center the galaxy, in the constellation of Sagittarius.
His discovery was widely publicized, appearing in the New York Times of May 5, 1933. Jansky wanted to follow up on this discovery and investigate the radio waves from the Milky Way in further detail. He submitted a proposal to Bell Labs to build a 30 meter diameter dish antenna with greater sensitivity that would allow more careful measurements of the structure and strength of the radio emission. Bell Labs, however, rejected his request for funding on the grounds that the detected emission would not significantly affect their planned transatlantic communications system. Jansky was re-assigned to another project and did no further work in the field of astronomy.
Several scientists were interested by Jansky's discovery, but radio astronomy remained a dormant field for several years, due in part to Jansky's lack of formal training as an astronomer. His discovery had come in the midst of the Great Depression, and observatories were wary of taking on any new and potentially risky projects.
Two men who learned of Jansky's 1933 discovery were of great influence on the later development of the new study of radio astronomy: one was Grote Reber, a radio engineer who singlehandedly built a radio telescope in his Illinois back yard in 1937 and did the first systematic survey of astronomical radio waves. The second was Prof. John Kraus, who, after World War II, started a radio observatory at Ohio State University and wrote a textbook on radio astronomy, still considered a standard by many radio astronomers.
In honor of Jansky, the unit used by radio astronomers for the strength (or flux density) of radio sources is the Jansky (1 Jy = 10-26 W m-2 Hz-1). Jansky crater on the Moon is also named after him. The NRAO postdoctoral fellowship program is named after Jansky.
A full-scale replica of Jansky's original rotating telescope is located on the grounds of the NRAO site in Green Bank, West Virginia, near a reconstructed version of Grote Reber's 30m dish.
C M B bye "wikipedia":
In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. It has a thermal 2.725 kelvin black body spectrum which peaks in the microwave range at a frequency of 160.4 GHz, corresponding to a wavelength of 1.9 mm. Most cosmologists consider this radiation to be the best evidence for the hot big bang model of the universe.
The standard hot big bang model of the universe requires that the initial conditions for the universe are a Gaussian random field with a nearly scale invariant or Harrison-Zel'dovich spectrum. This is, for example, a prediction of the cosmic inflation model. This means that the initial state of the universe is random, but in a clearly specified way in which the amplitude of the primeval inhomogeneities is 10-5. Therefore, meaningful statements about the inhomogeneities in the universe need to be statistical in nature. This leads to cosmic variance in which the uncertainties in the variance of the largest scale fluctuations observed in the universe are difficult to accurately compare to theory.
The cosmic microwave background radiation and the cosmological red shift are together regarded as the best available evidence for the Big Bang (BB) theory. The discovery of the CMB in the mid-1960s curtailed interest in alternatives such as the steady state theory. The CMB gives a snapshot of the Universe when, according to standard cosmology, the temperature dropped enough to allow electrons and protons to form hydrogen atoms, thus making the universe transparent to radiation. When it originated some 400,000 years after the Big Bang this time period is generally known as the "time of last scattering" or the period of recombination or decoupling the temperature of the Universe was about 3,000 K. This corresponds to an energy of about 0.25 eV, which is much less than the 13.6 eV ionization energy of hydrogen. Since then, the temperature of the radiation has dropped by a factor of roughly 1100 due to the expansion of the Universe. As the universe expands, the CMB photons are redshifted, making the radiation's temperature inversely proportional to the Universe's scale length. For details about the reasoning that the radiation is evidence for the Big Bang, see Cosmic background radiation of the Big Bang.
The Big Bang theory predicted the existence of the cosmic microwave background radiation or CMB which is composed of photons first emitted during baryogenesis. Because the early universe was in thermal equilibrium, the temperature of the radiation and the plasma were equal until the plasma recombined. Before atoms formed, radiation was constantly absorbed and re-emitted in a process called Compton scattering: the early universe was opaque to light. However, cooling due to the expansion of the universe allowed the temperature to eventually fall below 3,000 K at which point electrons and nuclei combined to form atoms and the primordial plasma turned into a neutral gas. This is known as photon decoupling. A universe with only neutral atoms allows radiation to travel largely unimpeded.
Because the early universe was in thermal equilibrium, the radiation from this time had a blackbody spectrum and freely streamed through space until today, becoming redshifted because of the Hubble expansion. This reduces the high temperature of the blackbody spectrum. The radiation should be observable at every point in the universe to come from all directions of space.
In 1964, Arno Penzias and Robert Wilson, while conducting a series of diagnostic observations using a new microwave receiver owned by Bell Laboratories, discovered the cosmic background radiation. Their discovery provided substantial confirmation of the general CMB predictionsthe radiation was found to be isotropic and consistent with a blackbody spectrum of about 3 Kand it pitched the balance of opinion in favor of the Big Bang hypothesis. Penzias and Wilson were awarded the Nobel Prize for their discovery.
In 1989, NASA launched the Cosmic Background Explorer satellite (COBE), and the initial findings, released in 1990, were consistent with the Big Bang's predictions regarding the CMB. COBE found a residual temperature of 2.726 K and determined that the CMB was isotropic to about one part in 105. During the 1990s, CMB anisotropies were further investigated by a large number of ground-based experiments and the universe was shown to be almost geometrically flat by measuring the typical angular size (the size on the sky) of the anisotropies. (See shape of the universe.)
In early 2003, the results of the Wilkinson Microwave Anisotropy satellite (WMAP) were released, yielding what were at the time the most accurate values for some of the cosmological parameters. (See cosmic microwave background radiation experiments.) This satellite also disproved several specific cosmic inflation models, but the results were consistent with the inflation theory in general.
Par amely1 le 13 Octobre 2006 à 00:47
Qu'est-ce que le "cosmic hisssss...." ???
voici un sujet qui touche plusieurs de mes travaux, il s'agit du cosmic hiss ou autrement appelé fond diffus cosmologique.
Il s'agit d'un rayonnement faible présent dans tout l'univers et qui se traduit et se ressent de differentes façon. Ce rayonnement provient du big bang, il est constant et permanent.
Comment le voir ou l'entendre ???
C'est la neige télé lorsque vous ne captez pas de chaine, ou le son émi lorsque vous cherchez une fréquence radio. Le bruit de ces ondes ( ou la neige télé) sont une partie de ce rayonnement appelé aussi micro-ondes, il est un echo du big bang.
D'où vient le nom "Cosmic hiss"
c'est le nom anglais de ce rayonnement, il fut decouvert par karl jansky dans les années 30, il capta le ce rayonnement par radio et l'entendi créant un bruit proche du "hissssssssss" une sorte de sifflement .
Voici les explications de wikipedia !
n 1928, il a rejoint les laboratoires de Bell Telephone dans le New Jersey. Les laboratoires Bell voulaient étudier la possibilité d'utiliser les ondes courtes (environ 10-20 mètres de longueur d'onde) pour le service radiotéléphonique transatlantique. Jansky était chargé d'étudier les sources parasites pouvant interférer avec ces transmissions vocales par radio.
Jansky construisit une antenne conçue pour capter les ondes radio à une fréquence de 20,5 mégahertz (environ 14,5 mètres de longueur d'onde). Cette antenne fut installée sur un plateau tournant, gagnant ainsi le nom de le manège de Jansky. En tournant l'antenne, on pouvait trouver la direction des signaux radios qui étaient captés.
Après avoir enregistré des signaux dans toutes les directions pendant plusieurs mois, Jansky identifia trois types de parasites : les orages voisins, les orages éloignés, et un sifflement faible mais régulier d'origine inconnue. Jansky passa l'année suivante à étudier ce troisième type de parasites. Les signaux commençaient et s'arrêtaient une fois par jour. Jansky crut d'abord qu'il captait des signaux provenant du Soleil. Mais en suivant le signal pendant quelques mois, il s'aperçut que l'origine du signal s'éloignait de la position du Soleil. Il remarque alors que le signal ne se répétait pas toutes les 24 heures, mais toutes les 23 heures et 56 minutes. C'est la période caractéristique des étoiles fixes et d'autres objets éloignés de notre système solaire : la durée d'un jour sidéral. Par la suite, il établit que ce signal provenait de la Voie lactée et était le plus intense dans la direction de son centre, dans la constellation du Sagittaire.
La découverte fut rendue publique, notamment dans le New York Times du 5 mai 1933.
Jansky voulut continuer sur la lancée de cette découverte et étudier plus en détail les ondes radio de la Voie lactée. Il proposa aux laboratoires Bell de construire une antenne parabolique de 30 mètres de diamètre. Mais les laboratoires de Bell avaient la réponse à leur question: les parasites n'étaient pas un problème pour la communication transatlantique par radio. Jansky fut assigné à un autre projet et ne fit plus de radioastronomie.
Beaucoup de scientifiques ont été fascinés par la découverte de Jansky, mais personne n'a poursuivi de recherches sur ce sujet pendant plusieurs années; c'était alors la Grande Dépression, et les observatoires ne pouvaient se permettre de s'engager sur de nouveaux projets.
Deux hommes ayant appris la découverte de Jansky en 1933 eurent plus tard une grande influence sur le développement de la radioastronomie. Le premier était Grote Reber ; en 1937, il construisit seul un radiotélescope dans son arrière-cour et fit le premier aperçu systématique du ciel par ondes radio. Le second était John Kraus ; après la Seconde Guerre mondiale, il fonda le premier radio-observatoire à l'université de l'État de l'Ohio et écrivit un manuel de radioastronomie qui est toujours la « bible » des radioastronomes.
En l'honneur de Jansky, l'unité employée par les radioastronomes pour l'intensité (ou plus exactement la densité de flux) des sources radio est le jansky (symbole: Jy). On a aussi nommé un astéroïde en son honneur : (1932) Jansky.
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