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Document1 1 of 22 pages 2nd class in PHS 207-02 & -S2 Astronomy Astronomical Tools Views of Orion nebula at 3 different wavelength ranges from http://www.rssd.esa.int/SD/INTEGRAL/docs/Publications/Science_In_School_issue20.pdf NAAP interactives as outside drive file: file:///F:/20122013/Salem%20State/fall%202012%20PHS%20272L/NAAP/Interactives/Astronomy%20Interac tives.htm OBJECTIVES What you learn about in this second class entitled astronomical tool are: The electromagnetic (EM) spectrum and what part it plays in our understanding of the universe 1 Document1 2 of 22 pages The detection devices such as telescopes at visible and radio frequencies as well as others and satellites The specific parts and applications of the optical telescope The limitations of these detection devices including our eyes and How digital technology is reducing our limitations Satellite images Building your own telescope NAAP telescope simulator http://astro.unl.edu/classaction/animations/telescopes/telescope10.html Introduction In this second class we are studying ways by which we detect and study the universe beyond us. Until robots landed or satellites encircled a heavenly object, practically the ONLY way (besides meteorites) has been by the signals an object emitted or reflected in the electromagnetic spectrum. EM SPECTRUM 2 Document1 3 of 22 pages The electromagnetic spectrum shown in figure 2.4 on page 34 is much more than the visible light we see. The higher frequency the faster the wave moves and the higher power required to generate that wave. This graph taken directly from Dr. Dinah Moche chapter 2 shows that we can see that only visible light, sub-millimeter, and radio waves penetrate our atmosphere and reach ground level. This is the principal reason for our satellites to detect what we can not and for optical and other telescopes high in the mountains where the atmosphere is thinner and hopefully less polluted. http://www.rssd.esa.int/SD/INTEGRAL/docs/Publications/Science_In_School_issue20.pdf Your cell phones operate around 3.9 GHz in the radio and microwave spectrum. The heat you feel from any warm object is in the infrared spectrum which is at higher frequencies than microwave and radio waves. The night vision goggles converts the infrared signals that any warm blooded animal emits into visible light. Ultraviolet is emitted by very hot gases. The light in a fluorescent light starts as ultraviolet and is converted by the fluorescent coating on the bulb into visible light. Even in this conversion fluorescent light is much more efficient than our common incandescent bulbs. X-ray allow doctors and others to see inside our bodies and identify different tissues by the amount of x-ray that is absorbed. Gamma-rays are the highest frequency and most powerful and pass through us and most every substance. What is important is what signals in each of those portions of the spectrum tells about what is likely to occurring to emit a given signal. A short video em spectrum http://imagine.gsfc.nasa.gov/Videos/general/spectrum.mov Short descriptions of each frequency range of the em spectrum http://science.hq.nasa.gov/kids/imagers/teachersite/UL3waves.htm Radio waves have the longest wavelength in the electromagnetic spectrum. These waves carry the news, ball games, and music you listen to on the radio. They also carry signals to television sets and cellular phones. Microwaves have shorter wavelengths than radio waves, which heat the food we eat. They are also used for radar images, like the Doppler radar used in weather forecasts. 3 Document1 4 of 22 pages There are infrared waves with long wavelengths and short wavelengths. Infrared waves with long wavelengths are different from infrared waves with short wavelengths. Infrared waves with long wavelengths can be detected as heat. Your radiator or heater gives off these long infrared waves. We call these thermal infrared or far infrared waves. The sun gives off infrared waves with shorter wavelengths. Plants reflect these waves, also known as near infrared waves. Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. These waves combine to make white light. Ultraviolet waves have wavelengths shorter than visible light waves. These waves are invisible to the human eye, but some insects can see them. Of the sun's light, the ultraviolet waves are responsible for causing our sunburns. X-Rays: As wavelengths get smaller, the waves have more energy. X-Rays have smaller wavelengths and therefore more energy than the ultraviolet waves. X-Rays are so powerful that they pass easily through the skin allowing doctors to look at our bones. Gamma Rays have the smallest wavelength and the most energy of the waves in the electromagnetic spectrum. These waves are generated by radioactive atoms and in nuclear explosions. Gamma rays can kill living cells, but doctors can use gamma rays to kill diseased cells. A VIDEO EXPLAINING EM SPECTRA http://www.natgeoeducationvideo.com/film/1178/the-electromagnetic-spectrum 2:25 MINUTES FROM NATIONAL GEOGRAPHIC 4 Document1 5 of 22 pages SIZE OF WAVELENGTHS THROUGH NATGEO http://scienceblogs.com/startswithabang/files/2012/10/EM_Spectrum3-new.jpeg A SECOND PICTURE http://pathstoknowledge.files.wordpress.com/20 09/05/electromagnetic_spectrum.png 5 Document1 6 of 22 pages http://www.sacta.co.za/Content/images/electro_diag.jpg Attenuation (reduction in signal) by the atmosphere http://www.rssd.esa.int/SD/INTEGRAL/docs/Publications/Science_In_School_issue20.pdf CHART OF SOURCE OF EM SPECTRUM 6 Document1 7 of 22 pages This chart assumes the sources obey the same laws as they would on our Earth. We have no reason to doubt that this assumption is true. This chart shows the likely source for a given spectrum. We will study those signals in more detail when we study star evolution after we study about our star the Sun. . EM spectrum http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html a fairly general explanation of the different spectrum within the electromagnetic spectrum with good graphics http://imagine.gsfc.nasa.gov/descriptions/spectrum.html 7 Document1 8 of 22 pages energy levels within frequency range http://imagine.gsfc.nasa.gov/docs/science/know_l1/spectrum_chart.html 8 Document1 9 of 22 pages What is the highest/energy wave? http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970412e.html 9 Document1 10 of 22 pages DETECTION DEVICES – TELESCOPES & SATELLITES The satellites which orbit above our atmosphere can detect these signals that we can not detect or can not detect easily on the Earth. The satellites also are not limited by the horizon and look at a portion of the sky for many more hours than we can. We will look at specific satellites of which the Hubble in the most well known That is the primary reason for satellites most cases to a level that we As the figure shows The signals are in the electromagnetic spectrum and range from radio waves to gamma rays in terms of frequency and power. OPTICAL TELESCOPE Refractory or reflectory telescopes Possible explanation of reflection and refraction (9 minute lecture but only first minute is worth using) http://www.youtube.com/watch?NR=1&v=Jvwm4hlzYmo&feature=endscreen Measures of a telescope (all assuming the telescope is stable or not wiggling around): the light gathering power, the resolving power, the magnification of a telescope, and field of view Background Notes on AMATEUR TELESCOPE OPTICS from http://www.telescope-optics.net/ On an early autumn day of 1608, Hans Lipperhey, a spectacle maker from Middelburg, in the Netherlands' coastal province of Zeeland, applied before the States General of The Hague for a patent on an "instrument for seeing far". By that time, use of small rounded glass disks to aid the natural eyesight wasn't new. Those bulging out on both sides, resembling lentil - or "lens" in Latin - have been used to correct for farsightedness since the mid 13th century. The idea of a device for magnifying distant objects may have been already grasped for some time as well. But this was the beginning of something else. In the summer of 1609, Galileo, Harriot, and others, turned the new Dutch invention - the "spyglass" - toward the night sky. The telescope was born. 10 Document1 11 of 22 pages NAAP telescope simulator http://astro.unl.edu/classaction/animations/telescopes/telescope10.html 11 Document1 12 of 22 pages The very basic element of a telescope is the diameter of its aperture. Given optical quality, it is the main determinant of telescope's capabilities with respect to light gathering and resolution, thus also of its limits in useful magnification. If well made, the eyepiece has no appreciable effect on the light gathering or inherent resolution of a telescope. Its main function is magnification of the real image formed by the objective. Consequently, the main optical parameters of a telescope relate to its objective. They are: ● aperture diameter, hereafter denoted by D ● focal length ƒ and ● relative aperture D/ƒ=1/F, with F being the focal ratio Thus, telescope consist from a single or or multi-element objective, and an eyepiece centered around the optical axis of the objective. The objective forms the focal point - a point of the highest generated wave energy or, geometrically, point of ray convergence on its optical axis - which determines the focal length of a telescope. Telescope focal length is a distance from the objective to where it focuses collimated light. That is, when the light arrives from objects far enough that the wavefront entering the objective is practically flat, and the light rays are practically parallel. 1.1. Diffraction image ► 12 Document1 13 of 22 pages 1. TELESCOPE IMAGE: RAY, WAVEFRONT and DIFFRACTION There are two main aspects to how telescopes form images of planets, stars and galaxies. One is concerned with the physics of image formation and the other with its geometry. We need the former to determine how light waves behave: where do they go, and how their interactions determine image brightness, contrast and resolution. The latter is an interface based on wave behavior that provides convenient way of determining image location and magnification, as well as the initial assessment of the size of image aberrations. By making space objects brighter and larger, telescopes greatly expand our ability of their detection and observation. the light energy directed toward focal point is spread into a pattern, setting a limit to image contrast and resolution. Physical size of diffraction pattern is inversely proportional to the telescope's relative aperture 1/F, with the first minima (Airy disc) radius given by rAD=1.22λF, λ being the wavelength of light, and F the focal ratio F=ƒ/D, ƒ and D being the telescope focal length and diameter, respectively. 1.1. DIFFRACTION IN A TELESCOPE Optically, any astronomical object is composed of a countless number of pointsources of light. The telescope forms object's image by imaging each and every of these point sources in its focal plane. The point-image itself is created by wave interference around focal point, a phenomenon known as diffraction of light. Diffraction image of a point-source in a telescope is a bright central disc surrounded by rapidly fainting concentric rings. What causes the appearance of this pattern is interference of light waves. Constructive interference is at its peak in the center of the pattern, which is the center of curvature of near-spherical wavefront formed by telescope's objective. Farther away from the center point, constructive interference quickly subsides, resulting in the first bright ring much fainter than the disc, and every successive bright ring much fainter than the preceding ring. Size of diffraction pattern in a telescope is proportional to the wavelength λ; given wavelength, its physical size is proportional to telescope's Fnumber, while its angular size is inversely proportional to the aperture size (FIG. 2). 13 Document1 14 of 22 pages 2. TELESCOPE FUNCTIONS The main purpose of astronomical telescope is to make objects from outer space appear as bright, contrasty and large as possible. That defines its three main function: light gathering, resolution and magnification. These are the measure of its efficiency. All three are related to some extent, but also have their individual characteristics and limits. 2.1. LIGHT GATHERING POWER Light-gathering power of a telescope mainly depends on its aperture diameter. However, it is the system light transmission that determines how much of the light that entered the telescope actually arrives at the final focus. Transmission losses occur due to reflection, scattering and absorption of light, as well as due to obstructions and diaphragms in the light path. Aperture directly determines how much of the light from distant objects is captured. Therefore, light-gathering gain of a telescope vs. naked eye is primarily due to its larger aperture. The naked eye pupil opening, at its widest, ranges anywhere from ~4mm to ~8mm in diameter, with 6mm being the most often cited average. Thus - neglecting for the moment transmission and possible obstructions - telescope of aperture D in mm will gather (D/6)2 times more light than an average eye. 14 Document1 15 of 22 pages How much of this light reaches the eye will depend on telescope's light transmission efficiency. Transmission losses at mirror surface range from ~2% to ~20%, or more. Light loss in glass elements, therefore, increases with the number of uncoated surfaces and the in-glass path length. For uncoated doublet objective, it is about 15% due to reflections, plus nearly 1% per inch of aperture due to in-glass absorption. For coated doublets, it is about 4% plus the absorption loss. The eyepieces are these days usually multicoated and, unless of exceptional size, have up to a few percent total light loss. Finally, most reflecting telescopes have central portion of their main mirror obscured by a smaller secondary mirror - so called central obstruction. Size of central obstruction is usually between ~0.15D to ~0.4D, resulting in ~2% -16% light loss. The true light-gathering power of a telescope is given by the product of its aperture area and transmission coefficient. At a rough average, light transmission is about 80% for amateur telescopes, although there are systems as low as ~60%, and those as high as ~95%. (The difference is often in the cost of the telescope.) Often times, light-gathering power of a telescope is expressed in terms of limiting stellar magnitude detectable. The apparent stellar magnitude - usually denoted by m - is a measure of apparent brightness, with the difference of 5 magnitudes corresponding to 100 times 15 Document1 16 of 22 pages difference in brightness. FIGURE 11: Limiting stellar magnitude as a function of telescope magnification, expressed as the ratio of the naked eye pupil diameter (E, for the naked eye limiting magnitude) and the telescope exit pupil X. For E/X=1 (blue line), background brightness in a telescope is identical as in the naked eye, and it doesn't affect limiting magnitude. As magnification increases, sky background becomes darker, enabling detection of fainter stars. As mentioned, choosing 6mm - or any other - naked eye pupil diameter does not affect the final limiting magnitude, since the naked eye gain/loss is offset by that with a telescope. But darker skies directly translate into higher limiting magnitude; in other words, if at this same 6mm eye pupil the limiting naked eye magnitude was higher, so it would be the limiting telescopic magnitude. 16 Document1 17 of 22 pages 2.2. TELESCOPE RESOLUTION Resolution is another vital telescope function. Simply put, telescope resolution limit determines how small a detail can be resolved in the image it forms. In the absence of aberrations, what determines limit to resolution is the effect of diffraction. Being subject to eye (detector) properties, resolution varies with detail's shape, contrast, brightness and wavelength. The conventional indicator of resolving power - commonly called diffraction resolution limit is the minimum resolvable separation of a pair of close point-object images, somewhat arbitrarily set forth by the wave theory at ~λ/D in radians for incoherent light, λ being the wavelength of light, and D the aperture diameter (expressed in arc seconds, it is 134/D for D in mm, or 4.5/D for D in inches, both for 550nm wavelength). Resolving two point sources is inevitably dependent on telescope magnification. If the images of two point of light are to be fully resolved, they need to be separated by at least a single non-illuminated retinal photoreceptor (presumably cone, since the resolution limit of rods is significantly lower). The point-source diffraction resolution limit for incoherent light, coherent light with λ/4 OPD between components and, perhaps, specific cases of partly coherent light, is given by ~λF, F being the ratio number of the focal length to aperture diameter (F=ƒ/D, with ƒ being the focal length). It is a product of angular resolution and focal length: λF=λƒ/D. Specifically, this is the limit to resolution for two point-object images of near-equal intensity (FIG. 12). 2.3. TELESCOPE MAGNIFICATION Telescope magnification is given by a ratio of the image size produced on the retina when looking through a telescope, versus retinal image size with the naked eye. As objective to 17 Document1 18 of 22 pages retina figure shows, image size on the retina in both cases is proportional to the apparent angle of view, giving telescope magnification …. For sufficiently small (angles) … gives telescope magnification as: with ƒO, ƒE being the objective and eyepiece focal length, respectively. Telescope magnification can be split into two components: (1) magnification of the objective and (2) magnification of the eyepiece. Magnification of the image formed by the objective is either relative to the object imaged (absolute, or optical magnification), or relative to its apparent size in the naked eye (apparent magnification). While there is no single optimum magnification for all types of astronomical objects and individuals, there is a range of so called useful magnification. On the low side of this range, the limit is set by the size of eye pupil. It is not to be smaller than the "exit pupil" of a telescope - an image of the entrance pupil (objective) formed by the eyepiece. Limit to magnification increase is set primarily by image imperfections, but also by dimming, loss of field, vibrations and eye physiology. As we have seen, even perfect optics will not produce perfect images, due to the effect of diffraction. The often quoted 50x per inch of aperture is a useful limit to magnification. Thus for our 20 inch Meade telescope the maximum useful gain is 1000. (20 x 50) Although other effects can limit to the value of ½ or a magnification of 500. TEST ON THE OPTICAL TELESCOPE NAAP telescope question summary the following two go together Just how I don't know http://astro.unl.edu/interactives/misc/Telescope1.html http://astro.unl.edu/interactives/misc/Telescope1.swf non-OPTICAL DETECTION DEVICES RADIO TELESCOPES 18 Document1 19 of 22 pages basics and scope of a radio telescope SATELLITES Employing satellites to record the universe eliminates atmospheric absorption of the electromagnetic spectra. X-ray 50 years of http://imagine.gsfc.nasa.gov/docs/features/exhibit/fifty/intro.html NASA Satellite by spectrum and function http://www.rssd.esa.int/SD/INTEGRAL/docs/Publications/Science_In_School_issue20.pdf European Space Agency satellites – some with NASA 19 Document1 20 of 22 pages European Space Agency satellites – some with NASA Future satellites James Webb Space Telescope http://www.nasa.gov/externalflash/webb3d/#/instruments/integrated-science-instrument-module/ 20 Document1 21 of 22 pages LIMITATIONS OF DETECTION DEVICES 1st limitation: Optical -- Most of the signals we receive we can not detected without electronic instrument. For our eyes can see all of thiese signals because they are outside of the light or optical frequencies. So we need instruments to detect and collect this energy and recognize and categorize it. Computers and detection devices like CCD, charge coupled devices, that have been developed in the last 70 years have enabled us to detected and categorized many of these signals. 2nd limitation -- atmosphere Our atmosphere that protects us from many harmful signals also prevents us from some of the signals coming from the universe. 3rd our optical vision – the geometry of the eye http://www.ivy-rose.co.uk/HumanBody/Eye/Eye_Image-Formation.php 4th limited viewing time – time available to view DIGITAL TECHNOLOGY Compare to human eye, to photographic, and to CCD, charge-coupled devices and digital technology NAAP CCD simulator http://astro.unl.edu/classaction/animations/telescopes/buckets.html Satellite images http://www.rssd.esa.int/SD/INTEGRAL/docs/Publications/Science_In_School_issue20.pdf Buying or building your first telescope Buying your first telescope from YouTube http://www.youtube.com/watch?v=lH5H9bf9gzo&feature=relmfu telescope building http://www.atmob.org/ Astronomical references 21 Document1 22 of 22 pages Astronomical dictionary http://imagine.gsfc.nasa.gov/docs/dictionary.html THE END 22