Přístroje pro astronomii 1

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1 Přístroje pro astronomii 1
Úvod kursu

2 Sylabus Historie astronomických pozorování, antické objevy a pozorovací metody, středověká astronomie, první dalekohledy a spektrometry. Spektrum elektromagnetického záření. Obloha v různých spektrálních oborech. Radiometrie a fotometrie. Úvod do geometrické a vlnové optiky. Paraxiální prostor, lámavé a odrazné plochy, Fermatův princip, Huyghens-Fresnelův princip, disperze, difrakční jevy, zobrazovací soustavy, zvětšení, zorné pole, rozlišovací schopnost, vinětace, světelnost, vady zobrazení. Čočkové dalekohledy. Achromáty, apochromáty, ED-optika. Korekce barevné vady. Korekce sklenutí pole. Reduktory a korektory. Prodloužení ohniska. Vady. Výhody a nevýhody. Zrcadlové dalekohledy. Newtonův dalekohled. Tří- a vícezrcadlové systémy. Vady. Výhody a nevýhody. Katadioptrické systémy. Maksutov, Cassegrain, Schmidtova komora, Schmidt-Cassegrain, Schmidt-Newton, Ritchey-Chrétien, Dall-Kirkham. Vady. Výhody a nevýhody. Montáže pro astronomické dalekohledy. Dobsonova montáž, vidlicová montáž, německá paralaktická montáž, speciální systémy. Některé velké profesionální systémy (např. Hale, Keck, VLT aj.) a jejich budoucnost. Aktivní optika. Adaptivní optika.

3 Co lze na obloze pozorovat okem
cca 6000 hvězd (celkem z obou polokoulí) 5 planet (6?), Měsíc, Slunce nejjasnější galaxie a mlhoviny (M31, M42) komety, meteory, supernovy, proměnné hvězdy rytmické a pravidelné pohyby – základ kalendářů

4 Cykly Chaldejský cyklus (7. stol. př.n.l., SAROS) – 41 zatmění Slunce (posunutých o třetinu obvodu Země) během cca 18 let Metonův cyklus (432 př.n.l.) – 19 tropických roků = 235 synodických měsíců [– 2 hodiny] Platónský rok (Hipparchos, 2. stol. př.n.l.) – precesní pohyb Země cca roků tropický rok - doba mezi dvěma po sobě jdoucími průchody Slunce bodem jarní rovnodennosti. Má délku 365,24220 středních slunečních dnů (365 d 5 h 48 min 45,71 s) synodický měsíc - Měsíc se vrátí do stejné polohy vůči Slunci z hlediska pozemského pozorovatele (29 d 12 h 44 min 2,8 s) – přibližně 29 ½ dne Platón měl na mysli přibližný společný násobek oběžných dob planet – zopakují se pohyby, Hipparchos pak precesní cyklus

5 Starověké observatoře
Goseck, Německo (4900 př.n.l.) Stonehenge, Velká Británie (~2-3 tis. př.n.l.) Kokino, Makedonie (1800 př.n.l.) Chankillo, Peru (4. stol. př.n.l.) El Caracol, Mexiko (906 n.l.) Goseck – zeimní a letní slunovrat Stonehenge – až 165 jevů (Gerald Hawking) Kokino – slunovraty, rovnodennosti Chankillo – 13 věží, sluneční kalendář El Caracol – cyklus Venuše, zatmění, rovnodennosti, slunovraty

6 Řecká astronomie (~600 př.n.l. - ~400 n.l.)
vycházeli z babylonských zdrojů Aristoteles – sféričnost Země, Slunce je větší než Země a hvězdy jsou podstatně dál než Slunce Aristarchus ze Samu – velikosti a vzdálenosti Slunce a Měsíce z pozorování zatmění heliocentrický model jako alternativa ke geocentrickému Hipparchos – první katalog hvězd zavedl hvězdné velikosti pokusil se potvrdit heliocentrický model změřením paralaxy, ale neuspěl sonda Hipparcos - High Precision Parallax Collecting Satellite Ptolemaios – geocentrický model - epicykly Almagest Aristoteles – Platonův žák, vychovatel Alexandra Makedonského

7 Příklad Sluneční světlo dopadá na dno hluboké studny ve městě Syena (dnes Aswan, jižní Egypt) v pravé poledne v den letního slunovratu. Téhož dne pozoruje Slunce Eratosthenes v Alexandrii mírně jižně od zenitu (cca 1/50 kruhu = 7.2°). Velbloudí karavana putuje ze Syeny do Alexandrie 50 dní průměrnou rychlostí 100 stadií denně. Spočtěte poloměr Země ve stádiích. Jak velké chyby se Eratosthenes dopustil? (atický stadion = 185 m, egyptský stadion = 157,5 m).

8 Orientální astronomie
Aryabhata (Indie, ) – výpočty poloh planet, zatmění, konjunkcí Supernova v souhvězdí Býka (1054) – zaznamenána čínskými a japonskými astronomy (mnoho dalších záznamů supernov a komet) Islámská astronomie Albumasar (9. stol.) – heliocentrický systém al-Sufi (10. stol) – katalog hvězd včetně barev, pozorování mlhovin v Andromedě a LMC Alhazen (11. stol.) – vysvětlil svit Měsíce …mnoho dalších

9 Antické astronomické pomůcky
Gnómon ukazatel slunečních hodin místní poledník určení rovnodennosti a zeměpisné šířky Astroláb (planisféra) otáčivá mapa hvězdné oblohy Armilární aféra prostorový model oblohy Mechanismus z Antikythéry úhloměr, sextant

10 Mechanismus z Antikythéry
př.n.l., řeckého původu (Hipparchos???) Objeven 1900 předpovědi pohybu Slunce a Měsíce (včetně excentricity měsíční dráhy), zatmění Mechanika na úrovni 18. stol. v Evropě

11 Renesance Mikoláš Koperník ( ) – navrhl heliocentrický systém (De revolutionibus orbium coelestium) Tycho de Brahe ( ) – velmi přesná měření ~ 1’ Slunce, Měsíce a planet (mnohaletá), také supernovu v roce 1572 Johannes Kepler ( ) – vysvětlil pohyby planet (Keplerovy zákony, Astronomia nova, Harmonices Mundi) Galileo Galilei ( ) – propagoval koperníkovský heliocentrismus (Dialogo sopra i due massimi sistemi del mondo), využíval hojně dalekohled, objevil čtyři Jupiterovy měsíce a sluneční skvrny, fáze Venuše, hvězdy v Mléčné dráze Isaac Newton ( ) – teorie gravitace (Philosophiæ Naturalis Principia Mathematica), vynalezl první dalekohled s odrazným zrcadlem, rozložil bílé světlo hranolem

12 Proč potřebujeme dalekohledy a CCD detektory?
zvýšení sběrné plochy pro světlo oko má sběrnou plochu mm2 dalekohledy ji zvětšují krát integrace sběru fotonů v čase oko 100 ms (skotopicky), 10 ms (fotopicky) zvýšení rozlišovací schopnosti oko asi 1' fotopicky asi 5' skotopicky

13 Technologická revoluce
velké dalekohledy fotografie fotonásobiče, intenzifikátory obrazu CCD kamery počítače

14 Neoptická astronomie Radioastronomie (Jansky, 1931) – kvazary, pulzary
Sekundární projevy dopadu vysokoenergetických částic do atmosféry Kosmická astronomie Rentgenová – neutronové hvězdy, rázové vlny při výbuchu supernov UV a IR – vznik hvězd Gama – pulzary, aktivní jádra galaxií Planetární průzkum – sondy a roboti Částicová astronomie – protony, neutrina Gravitační vlny

15 Stručná historie objevů
1802 Fraunhofer identifikoval absorpční čáry ve slunečním spektru a zjistil že odpovídají prvkům známým na Zemi Model nukleární pece ve hvězdách (jaderná fyzika 1. pol. 20. století) velmi dobře předpovídá chování a velikosti hvězd, nedávno potvrzen i měřením toku slunečních neutrin 1862 – pozorován první bílý trpaslík (Sirius B) – velikost Země, ale hmotnost Slunce – degenerovaný elektronový plyn (vysvětlen kvantovou teorií ve 20. letech 20. století)

16 Stručná historie objevů
1939 – existují ještě kompaktnější objekty – neutronové hvězdy: hmotnost Slunce, ale 1000x menší než bílý trpaslík (objeveny jako pulzary a později jako rentgenové hvězdy) život hvězd – zárodečné mlhoviny protohvězdy – otevřené hvězdokupy – obři a trpaslíci - novy – supernovy – planetární mlhoviny – kulové hvězdokupy

17 Stručná historie objevů
1917 Shapley – velikost naší Galaxie 1924 Hubble – vzdálenost galaxie v Andromedě 1929 Hubble – galaxie se vzdalují – vesmír se rozpíná Kosmologie velkého třesku

18 Bible Genesis 1:1 Na počátku stvořil Bůh nebe a zemi.
Jób 38:4 Kde jsi byl, když jsem zakládal zemi? Pověz, víš-li něco rozumného o tom.

19 Současné výzvy gravitační vlny (pozorování binárních pulzarů)
oscilace neutrin inflační vesmír temná hmota a temná energie rozpínání se zrychluje (NC2011) fluktuace CMB neutrina rychlejší než světlo?

20 Informace o vesmírných objektech
světlo (fotony) vlnově-částicová povaha interferometrie šíří se po přímých drahách (kromě nízkofrekvenčních rádiových vln a ohybu na gravitačních čočkách) kosmické záření (nabité částice) zejména protony, ale i těžší jádra působí na ně mezihvězdná a mezigalaktická magnetická pole meteority – informace o sluneční soustavě neutrina gravitační vlny

21 Jednotky „energie“ vln. délka, frekvence, energie, vlnočet,  = c
Foton λ = 1 μm má ν = 3 x 1014 Hz E = hν = 2 x J elektronvolt: 1,24 eV (1 eV = 1,602 x J) převrácený centimetr: 104 cm-1 μm, nm, angström GHz, THz, PHz, EHz Pro plyn v termodynamické rovnováze (černé těleso) hν = kT ν [Hz] ≈ 2 x 1010 T [K]

22 Spektrum el.-mag. záření

23 Propustnost atmosféry

24 Propustnost atmosféry

25 Mezihvězdný prach

26 Turbulence atmosféry Obraz v dalekohledu se při krátké expoziční době (< ms) rychle mění Při dlouhé expoziční době je rozmazaný diffraction- -limited „tip/tilt“ 21 min

27 Charakterizace míry turbulencí v atmosféře
Prostorové vlastnosti: Friedův parametr r0 - velikost apertury, jejíž difrakčně omezená rozlišovací schopnost by byla stejná jako rozlišovací schopnost nekonečně velké apertury daná turbulencemi atmosféry „seeing“ ε - velikost difrakčního obrazce daného turbulencemi Časové vlastnosti: Na krátkých časových škálách [10-2 – 10-3 s] – speklový dekoherenční čas τ0 Na delších časových škálách [sekundy až hodiny] - časový interval t0, po který je možné považovat obraz za translačně stabilní Izoplanatický úhel Maximální úhlová vzdálenost objektů θ0, které jsou deformovány velmi podobnými distorzemi vlnoplochy (definice je vágní...)

28 Závislost na nadmořské výšce

29 Závislost na vlnové délce

30 Závislost na zenitovém úhlu

31 Obloha v různých spektrálních oborech
73,5 cm, 1,7x10-6 eV 0,37 nm, 6 keV 3,5 μm, 0,36 eV 1,2x10-5 nm, >100 MeV 240 μm, 5,2x10-3 eV 500 nm, 2,5 eV

32 Obloha v různých spektrálních oborech

33 Galaxie (M31) The visible-light images above reveal the general pinwheel characteristic of spiral galaxies: a bright central bulge, graceful spiral arms twisting about the bulge, and lanes of dust within the thin disk. Young and massive stars tend to be blue and the color image vividly shows that such stars are preferentially born within the arms of a spiral galaxy. The condensations of dust within M31 are typically mixed with molecular gas (which is best seen at radio wavelengths; see below). Such gas and dust are the raw materials from which future stars are born. Two other Messier objects, both smaller dwarf elliptical galaxies, are also seen in the images above. Messier 32 is the companion immediately south of Andromeda, and Messier 110 is the galaxy located to the northwest (upper right). These small satellite galaxies are both gravitationally-bound to the much larger Andromeda Galaxy. They contain from 1-10 percent of the mass of M31 and are a factor of 10 or more smaller in spatial extent.       Mid-Infrared: Spitzer, Mid-Infrared: IRAS, and Far-Infrared: ISO The infrared images shown above, obtained by different space-borne observatories, display similar aspects of Messier 31. While the brightest emission originates in the galaxy center, the most prominent features are the ringsof infrared light circling the galaxy. It is within these rings that vast numbers of new stars are being born. One can also see traces of the inner spiral arms of M31. The image to the left is a 24 micron view from the Spitzer Space Telecope. Spitzer detects dust heated by stars in the galaxy. Its multiband imaging photometer's 24-micron detector recorded approximately 11,000 separate infrared snapshots over 18 hours to create the new comprehensive mosaic. This instrument's resolution and sensitivity is a vast improvement over previous infrared technologies, enabling scientists to trace the spiral structures within Andromeda to an unprecedented level of detail. The galaxy's central bulge glows in the light emitted by warm dust from old, giant stars. Just outside the bulge, a system of inner spiral arms can be seen, and outside this, a well-known prominent ring of star formation. The middle image represents a composite photograph taken by the Infrared Astronomical Satellite (IRAS) satellite at longer infrared wavelengths: 25 and 60 microns. Once again, the most luminous region is the center of the Andromeda Galaxy (shown in white). The ring is once again clearly visible. Moreover, the brightest condensations within the ring (depicted as white and red) correspond to the same bright enhancements seen in the Spitzer image. The 175 micron IR image (above right) was taken by the European Space Agency's Infrared Space Observatory, which orbited from 1995 through The prominence of the central core is diminished, while the outer ring is still easily visible. Why is that? Mid- and far-infrared light is a tracer of dust. However, the temperature of the dust can vary, and depends on the amount of ambient visible and ultraviolet light absorbed and re-radiated by the dust particles. The peak emission from hotter dust occurs at shorter wavelengths than that from cooler dust. Because of the great density of illuminating stars near the center of a spiral galaxy, one can predict that the dust will be warmest in those regions. The coolest dust is likely to be in the outer regions of the galaxy disk, where the surrounding density of stars is less (see visible-light photos at top of page). This prediction is confirmed by comparing the IRAS and ISO photos. The bright central regions are seen best at the shorter wavelengths observed by IRAS. The ISO results measure cooler dust, and hence are more tuned to seeing the dust in the outer portions of the disk. Note how the IR emission even extends beyond the bright ring, to the outer edges of the galaxy disk. To see what the far-infrared image would look like if we could see the Andromeda Galaxy in a face-on orientation face-on, click here for a mathematical re-projection of the data.     Mid-Infrared: IRAS and Radio: Effelsberg The radio image of M31 (above right), obtained at a wavelength of 6 cm, is paired with the IRAS mid-IR photo (above left) for easy comparison of features. Red denotes the brightest regions within the radio data obtained by the largest radio telescope in Germany. The first thing one notices is that the central core of Andromeda and the ring are once again prominent. Astronomers have found that the spatial distribution of radio continuum (broadband) emission in spiral galaxies closely tracks that of far-infrared emission. The massive stars born in supergiant HII regions burn their fuel very fast, and have short lifetimes (by cosmological standards). Such stars often produce supernova explosions when they die, and these explosive events yield significant amounts ofsynchrotron radio emission. In the long continuum of astronomical time, the images in this Gallery essentially represent a near-simultaneous snapshot, revealing both star birth and star death occurring in the same era. Hence, we see both infrared and radio light. The physical emission mechanisms differ, but both arise from the same population of massive stars, albeit at different stages of their life. The other notable features within the radio data are the bright blobs of emission scattered in an apparently random manner throughout the photograph. The fact that these point-like emission sources are not confined within Messier 31 immediately tells us that they are either in the nearby foreground (that is, within our Milky Way) or are in the distant background. Quasi-stellar objects (also known as quasars, or QSOs) are among the most luminous objects in the Universe and are found at great distances from us (billions of light years). Many quasars emit intensesynchrotron radiation at radio wavelengths, usually powered by a central black hole. A search of the NASA/IPAC Extragalactic Database (NED), conducted within 2 degrees of the center of M31, reveals only four cataloged quasars. Since there are many more sources of radio emission in the field, we conclude that most of the observed quasars are still uncataloged by astronomers.   Ultraviolet: GALEX The GALEX ultraviolet image shows blue regions of young, hot, high mass stars tracing out the spiral arms where star formation is occurring, and the central orange-white "bulge" of old, cooler stars formed long ago. The red stars in this image are foreground stars in our own Milky Way galaxy.   X-Ray: ROSAT At x-ray wavelengths (above right), the central regions of Messier 31 are clearly seen. Again, this is primarily due to its proximity. Most distant normal galaxies (like M31) are not strong x-ray sources. Active galaxies, on the other hand, are often strong emitters of x-rays. These types of objects include quasars and various types of objects that are collectively known as active galactic nuclei (AGN). The handful of the brightest point sources seen scattered throughout the x-ray image is likely due to emission from distant QSOs and AGN in the background. 

34 Aktivní galaxie (M51) The "Whirlpool Galaxy" (Messier 51) is a splendid example of a face-on spiral galaxy gravitationally interacting with a smaller companion galaxy. The spectacular spiral galaxy is also commonly known as NGC 5194, and the smaller companion as NGC 5195, and both are found in the constellation of Canes Venatici.       Visible: Tony and Daphne Hallas (left), Visible: TIE (center) and Near-Infrared: 2MASS (right) The two visible-light images and the near-infrared image display similar features, with varying sensitivities (due to different photographic exposure times). The long-exposure color image (left) clearly shows the sweeping spiral arms and the fact that the arms include patchy knots of star formation. The companion galaxy, which is classified as an irregular galaxy, lacks the well-defined structure of a spiral galaxy and appears "attached" to the end of a spiral arm in the "Whirlpool Galaxy". The short-exposure TIE image (center) beautifully reveals the opaque dust lanes within the spiral arms of the spiral galaxy (e.g. at the 1-2 o'clock position in the inner arm). These arms are rich in molecular gas and dust, the raw materials from which stars are born. The blue tint to the arms in this color photograph reflects the fact that spiral arms are the preferential location for the formation of Type O and Type B stars, the hot blue-white stars characterized by large masses and short lifetimes. The near-infrared image (right) roughly traces the general pattern of spiral arms in NGC However, near-infrared wavelengths are best for studying older and less massive stars. Hence, the spiral arms, which are dominated by young blue stars, are less prominent in the 2MASS photograph.   Far-Infrared: IRAS Turning your attention to the low-resolution far-infrared image of M51 (above), we see three features: the central core of the spiral galaxy, its two major arms (green) to the upper left and lower right of the center, and the companion galaxy to the north. The spiral arms are barely discerned as emission blobs adjacent to the center of NGC Far-IR wavelengths are effective for mapping the distribution of dust in galaxies, and as the TIE image showed (above), the "Whirlpool" is rich in dust. [Remember that the IRAS detectors were rectangular, and hence emission features in the far-IR image are stretched along one dimension; in this case, along a line running from the lower left to the upper right.]     Radio: VLA (left) and X-Ray: Chandra (right) In a similar manner, the radio image (above left) broadly traces the same distribution of light seen in the earlier photos. The spiral arms extending from the galaxy center and the companion galaxy are clearly seen at radio wavelengths. A modest-sized red blob appears to be connected to the end of the southern spiral arm, located about 5 arcminutes to the southeast of the M51 center (8 o'clock position). This is probably a background quasar, and is also seen as a small source in the x-ray image. Many of the distant quasi-stellar sources are strong sources of both radio and x-ray emission. The other radio feature towards the eastern (leftward) edge of the image is not seen at x-ray wavelengths, and its origin is uncertain. The x-ray image highlights the energetic central regions of the two interacting galaxies. Much of the diffuse glow is from multi-million degree gas. Many of the point-like sources in the x-ray image are due to black holes and neutron stars in binary star systems.   Infrared 15 microns - ISO Finally, we include a "bonus image" from the European Space Agency's Infrared Space Observatory (ISO). This space-borne observatory operated from , and represented a powerful second-generation capability beyond IRAS. This particular image was taken with a camera operating at a wavelength of 15 microns (15,000 nm), a region referred to as the mid-infrared. This wavelength is intermediate between those of the 2MASS near-infrared and IRAS far-infrared, and has better spatial resolution than IRAS. Mid-IR light is well-suited to studying star formation and tracing dust in spiral galaxies. This image not only shows the galaxy cores and spiral arms, but nicely illustrates the knots of star formation occurring in the arms of M51.    Ultraviolet: GALEX The ultraviolet image from GALEX maps the hotter stars in this galaxy. 

35 Krabí mlhovina (M1) The Crab Nebula (Messier 1), located in the constellation of Taurus, is a supernova remnant (SNR), the result of a cataclysmic supernova explosion in the year This explosive death of a star was so bright that it could be seen in the daytime sky for 23 days, and was documented by astronomers throughout the Far East.     Visible: DSS (left) and Visible: TIE (right) Let us begin by comparing two visible-light photos (above), taken with different telescopes. Note that the DSS image is a longer exposure than the TIE photo. How can you tell? Because the diffuse (fuzzy) emission from the nebula is overexposed in the DSS picture, and because the surrounding field shows a greater density of stars. In general, a longer photographic exposure will reach out to deeper space and to fainter objects; in other words, it will achieve greater sensitivity. Apart from this difference, the optical images appear similar -- as they should!   Visible: Color Credit: FORS Team, 8.2-meter VLT, ESO This visible-light color photo illustrates the complex composition of the Crab Nebula. The gaseous filaments are the result of the cataclysmic explosion that blasted the star's outer shell into space. At the center of the nebula, a rapidly spinning neutron star is spinning at the rate of about 30 times a second! This pulsar is too faint to be seen in these images.     Near-Infrared: 2MASS (left) and Visible: TIE (right) The near-infrared image also appears similar to the visible-light photographs. This is partly because near-infrared wavelengths are only slightly longer than the (red) visible-light region of the electromagnetic spectrum. Try selecting any star pattern near the edge of the nebulosity in the near-IR image. [There will not be a perfect correlation between relative stellar brightnesses, because some stars appear brighter in visible than in near-IR, and vice versa.] Now locate that same pattern of stars in the visible-light (TIE) image. You should find that the pattern appears farther away from the diffuse emission, suggesting that the 2MASS near-IR image reaches a slightly greater sensitivity than the TIE optical image. How can you confirm this?       Near-Infrared: 2MASS (left), Mid-Infrared: Spitzer (middle) and Far-Infrared: IRAS (right) Now examine the mid-infrared (middle) and far-infrared images (right) of the Crab Nebula, and compare them with the near-infrared picture (left). Like most images of astronomical phenomena, the mid- and far-IR images are false-colored. The Spitzer image is a composite of images from Spitzer's Infrared Array Camera (IRAC) and Multiband Imaging Photometer (MIPS) at 3.6 (blue), 8.0 (green), 24 (red) microns. This view of the supernova remnant obtained by the Spitzer Space Telescope shows the mid-infrared view of this complex object. The blue region traces the cloud of energetic electrons trapped within the star's magnetic field, emitting so-called "synchrotron" radiation. The yellow-red features follow the well-known filamentary structures that permeate this nebula. Though they are known to contain hot gasses, their exact nature is still a mystery that astronomers are examining. The energetic cloud of electrons are driven by a rapidly rotating neutron star, or pulsar, at its core. In the far-infrared image, the brightest regions are depicted in red, intermediate brightness in green, and the faintest emission is in blue. We do not see much detail at the far-infrared wavelengths! You see a central concentration of infrared emission, but not much else. Why does the far-infrared emission look so different from the near and mid-infrared? There are two reasons. First, these types of infrared radiation are produced by different physical processes. Near-infrared light is similar to very long-wavelength red light, and is often generated by the same processes that produces visible light from stars. Mid- and far-infrared radiation, on the other hand, is true thermal emission (or heat). Its presence is often a signature of cosmic dust, and results from the dust particles absorbing ultraviolet and visible light, and re-radiating at lower energies (longer wavelengths) in the infrared. Second, the spatial resolution (ability to discern detail) of the IRAS far-infrared detectors was about 10 times worse than the optical and near-infrared data shown above. Hence, far less detail is seen in the IRAS maps, and individual picture elements (pixels) can be seen clearly.     Radio: NRAO (left) and Mid-Infrared: Spitzer (right) Now turn your attention to the radio image (above left). Supernova remnants typically emit large amounts of non-thermal synchrotron radio emission, and the Crab Nebula is no exception. This type of radiation is a result of fast-moving, high-energy electrons spiraling about magnetic field lines. The general shape and orientation of the radio emission from the nebula resembles the previous images. In general, the distribution of radio emission often resembles that of mid- and far-IR light.   X-Ray: Chandra The X-ray image shows high-energy emission from fast-moving particles in the central region of the Crab Nebula and reveals a brilliant ring around the nebula's heart. The image shows tilted rings or waves of high-energy particles that appear to have been flung outward over the distance of a light year from the central star, and high-energy jets of particles blasting away from the neutron star in a direction perpendicular to the spiral.       Ultraviolet: ASTRO-1 UIT (left) Visible: TIE (center) and Near-Infrared: 2MASS (right) Finally, the ultraviolet image (above left) resembles the shape and configuration of the optical and near-infrared images. Note that the notch to the east of center (at the 9 o'clock position) matches the shape and size of the near-infrared image. The point sources scattered about the field of view are foreground and background stars in our Milky Way. The most likely candidates for UV emission are the youngest, hottest and most massive stars (denoted as types O and B). 

36 Slunce The Sun that dominates our daytime sky and provides the thermal (heat) energy necessary to support life on Earth is of course -- a star. Its proximity to Earth, at about 150 million kilometers, allows us to study its surface and to characterize this average star with unprecedented detail. In terms of the speed of light, the Sun is about 8-1/3 light minutes from us. The next nearest star is about 4 light years away! The Suns diameter is about half a degree, the same as the full moon. Because of its high luminosity, astronomers often use specialized telescopes to study the Sun. Hence, the sources of images for this particular gallery are different from most of the others in our online Museum. Lets study some of the images displayed in the above matrix.     Visible: White Light: and Visible: Calcium-K The two images above were obtained at California's Big Bear Solar Observatory. The white light image (above left) is the result of collecting all of the visible light waves (that is, all of the colors in the rainbow). The black-and-white image shows the solar photosphere, with a diameter of about 1.4 million kilometers. [Photos is the Greek word for light.] While the Sun is essentially a very large ball of glowing gas, the photosphere is normally taken to define the solar surface, the region where most of the light originates. The temperature of the photosphere is about Kelvin (K), or degrees (Celsius) above absolute zero. The dark splotches on the leftmost (eastern) limb, and scattered elsewhere in the image, are sunspots. These features are cooler than elsewhere in the image, are sunspots. These features are cooler than the surrounding photosphere and are associated with regions of high magnetic fields. Sunspots can be tracked across the face of the Sun as it rotates (with proper viewing precautions, of course!). Whereas the earth rotates every 24 hours, the Sun has a differential rotation period. The rotation periods vary from 25 days at the equator to 36 days at the poles. Sunspot appearances vary on timescales ranging from days to weeks. For a close-up look at a sunspot, click here. The other black-and-white photograph (above right) is the result of passing the Suns visible light through a narrow-band filter, to selectively detect only light of a particular wavelength. In this case, the Calcium-K filter measures blue light at a wavelength of 393 nanometers (nm). The source of this light is the chromosphere, and is hotter (6000 K to 20,000 K) than the underlying solar photosphere. [Chromos is the Greek word for color.] The (dark) graininess of the photo is due to a solar feature called supergranulation. These convection cells are larger than the diameter of the Earth, and signify that hot gas is being vertically transported within the chromosphere, much like bubbles in a boiling pot of water. To ascertain what is happening within the white portions of the Calcium-K image, compare their positions on the disk to those of the sunspots seen in the other photograph above (taken a short time earlier). The positions are similar! Apparently, the strong magnetic fields associated with sunspots tend to inhibit the formation of supergranules in the chromosphere.   Visible: Hydrogen-Alpha The color image (above) is taken through another visible-light filter, and was obtained at the Learmonth Solar Observatory in Western Australia. The hydrogen-alpha filter admits red light at a wavelength of 656 nanometers, also originating in the solar chromosphere. The lighter regions again correspond to regions with sunspot activity.   Infrared: NSO The near-infrared image (above) of our Sun was obtained at a wavelength of 1083 nm (or microns) at theNational Solar Observatory atop Kitt Peak in Arizona. The darker regions are areas where the gas is cooler and denser, and where some of the IR light is absorbed. If you look closely at the southwest (lower right) limb, you may be able to see a solar prominence. This is an eruption of gas from within the solar corona, the outermost layer of the Sun. In this region, the temperatures reach two million degrees!     UV: Soho: and EUV: SOHO The ultraviolet (UV) and extreme-UV (EUV) photographs (above), at wavelengths of 19.5 nm and 30.4 nm respectively, were obtained by the Extreme Ultraviolet Imaging Telescope aboard the space-borne Solar and Heliospheric Observatory (SOHO), a collaboration between the European Space Agency and NASA. The UV light originates from the upper chromosphere and lower corona, whereas the EUV light comes from lower regions in the chromosphere. At these wavelengths, we are starting to observe active regions, denoting some of the higher energy phenomena associated with the Sun. These include such features as flares and coronal mass ejections. Lighter regions correspond to the hottest, or most energetic, regions.   X-ray: Yohkoh The spectacular x-ray image of the Sun was obtained by the Japanese observatory Yohkoh (Sunbeam), a collaborative effort with the US and UK. Launched in 1991, Yohkoh took the above image at wavelengths corresponding to a few nanometers, and these x-rays originate from the Suns corona. Note the amazing variety of coronal loops and streamers, seen in edge-on projections along the solar limb. Darker regions denote cooler areas where the gas is more quiescent (less active) and denser.   Radio: Nobeyama We close our solar journey with a quick look at a radio image (above) taken from Japan's Nobeyama Radio Observatory at a wavelength of 1.7 centimeters. As in the other photos, the most active regions are the most luminous. Would you like to know more about the Sun, see additional images and movies, and try out some interesting classroom activities? Then we suggest you visit YPOP, the Yohkoh Public Outreach Project. This excellent NASA-supported educational site is a collaborative effort between Lockheed Martin Solar and Astrophysics Lab in Palo Alto, California and Montana State University in Bozeman. Would you like to see the latest images of the Sun? Then visit the SOHO Web site!

37 Úvod do radiometrie spektrální hustota záře (spectral radiance, specific intensity) Lν [W m-2 sr-1 Hz-1], Lλ [W m-3 sr-1] zář (radiance, luminance) – celé spektrum L [W m-2 sr-1] kosinový (Lambertovský) zdroj intenzita vyzařování (do poloprostoru) [W m-2] (radiant exitance, flux) F = ∫L cos(θ) dΩ = πL Fν (flux density)[W.m-2.Hz-1, Jy=10-26 W.m-2.Hz-1] zářivost (radiant intensity) I [W sr-1] zářivý tok (total flux, luminosity), Φ [W] = FA zářivá energie Q [J]

38 Záření černého tělesa

39 Ozáření Ω=a/r2=4π sin2(θ/2)
Intenzita ozáření (irradiance) E=FA/(4πr2)=AL/(4r2) [W m-2] Ozáření H = ∫E(t) dt [J m-2] - expozice propustnost, filtrace T PD≈AaTLλ(λ0)Δλ/r2 [W]

40 Fotometrie Zářivá energie, jak je vnímána lidským okem
Světelný tok [lm] místo zářivého toku [W] Radiometrie Fotometrie zářivý tok (radiant flux, luminosity) Φ [W] světelný tok (luminous flux) [lm] intenzita vyzařování (radiant exitance) F [W.m-2] světlení (luminous exitance) [lm.m-2] zářivost (radiant intensity) I [W.sr-1] svítivost (luminous intensity) [cd = lm.sr-1] zář (radiance) L [W.m-2.sr-1] jas (luminance) [nt = cd.m-2] intenzita ozáření (irradiance) E osvětlení (illuminance) [lx = lm.m-2] ozáření (radiant exposure) H [J.m-2] osvit (light exposure) [lx.s]

41 Typické hodnoty Zdroj Jas [nt] Osvětlení [lx] Slunce v zenitu
105 zamračená obloha 40 Měsíc 2500 0,2 noční obloha 5 x 10-5 0,001

42 Zdánlivé magnitudy nelinearita odezvy lidského oka (1:10:100)
Hipparchos, N.R.Pogson (1856) – intenzita vyzařování hvězdy 1. velikosti je asi 100-násobek hvězdy 6. velikosti, neboli mezi sousedními hvězdnými velikostmi je podíl m = -2,5 log10(F/F0) (F0 závisí na konkrétním fotometrickém systému) m1 - m2 = -2,5 log10(F1/F2) mv vizuální magnituda mpg fotografická magnituda mbol = mv – BC bolometrická magnituda

43 Fotometrické systémy UBV systém UBVRI systém uvby systém
…mnoho dalších

44 Absolutní magnitudy absolutní magnituda M je číselně stejná jako zdánlivá magnituda m ze vzdálenosti 10 pc m -M = -2,5 log10[F (r)/F (10)] = = -2,5 log10[10 pc/r]2 = 5 log10[r/10 pc] vztah k zářivému toku: Mbol = -2.5 log10[Φ/Φ0], Φ0 = 3,0x1028 W

45 Zdánlivá magnituda dvojhvězdy
Jakou celkovou zdánlivou magnitudu má dvojhvězda, která se skládá ze složek se zdánlivými magnitudami 1m a 2m ? 1 = -2.5 log10(F1/F0), 2 = -2.5 log10(F2/F0) F1 = F0 x 10-0,4, F2 = F0 x 10-0,8 F = F1 + F2 = F0 (10-0, ,8) m = -2,5 log100,5566 = 0,64

46 Studijní materiál