Reflecting And Refracting Telescopes

Reflecting And Refracting Telescopes The telescopes invention is often pegged in 1608 with the award of a patent to Lippershey by the States-General, the name for parliament in the Netherlands. However, an Englishman, Thomas Harriott constructed an early, low-power version of the telescope and used it in August 1609 to observe the Moon, at the same time when Galileo presented a similar small instrument to the Venetian Senate. Galileo undertook his own serious observations in October or November of that same year with a larger telescope. Hans Lippershey , a Dutch eyeglass manufacturer,is most often associated with the invention of the telescope. Lippershey was awarded a patent for his device in October 1608 by the parliament in the Netherlands.Credit for the invention of the telescope is also extended to Jacob Metius, a Dutch optician, though he was reluctant to allow the Dutch parliament to review his patent claim and even prohibited anyone from seeing his device. Despite his reluctance, Metius was eventually awarded a small sum from parliament, also in 1608, when he applied for a patent on his device a few weeks after Lippershey.However, the Dutch parliament only allowed Lippershey to construct a binocular version of his telescope. So, Lippershey is also the inventor of the binocular! ( note: Galileo Galilei did not invent the telescope!) TELESCOPE DIMENSIONS Aperture: The diameter of the primary mirror or lens. This determines the limiting magnitude and the angular resolution. Focal Length: The length it takes the light to converge to a single point. A smaller focal length increases magnification and brightness, whereas a longer focal length has the opposite effect. This makes a difference only for extended objects, not stars. Magnifying Power: (focal length of eyepiece)/(focal length of telescope). F/Ratio: (focal length of telescope)/aperture. A ratio of 8 is written f/8. Focal Plane: The plane perpendicular to the point of convergence. PARAMETERS OF TELESCOPE The utility of a telescope depends on its ability to collect large quantities of light and to resolve fine details. The brightness of an image is proportional to the area of the light-gathering element, which is proportional to the square of that elements aperture. The brightness also depends on the area over which the image is spread. This area is inversely proportional to the square of the focal length (f) of the lens. The brightness of the image therefore depends on the square of the f/ratio, just as in an ordinary camera. The resolving power of a telescope depends on the diameter of the aperture and the wavelength observed; the larger the diameter, the smaller the detail that can be resolved. TYPES OF TELESCOPES We will be primarily concerned with optical telescopes which have two basic subdivisions: Refracting Telescopes: Refraction works on the principle that light has different bending properties in different media (glass,water, air, etc.). Refracting Telescopes use a glass lens to cause the convergence of the light. Reflecting Telescopes: Reflecting telescopes use mirrors (concave or convex) to direct incoming light to converge to a point. REFRACTING TELESCOPES Small refracting telescopes are used in binoculars, cameras, gunsights, galvanometers, periscopes, surveying instruments, rangefinders, astronomical telescopes, and a great variety of other devices. Parallel or nearly parallel light from the distant object enters from the left, and the objective lens forms an inverted image of it . The inverted image is viewed with the aid of a second lens, called the eyepiece. The eyepiece is adjusted (focused) to form a parallel bundle of rays so that the image of the object may be viewed by the eye without strain. The objective lens is typically compound; that is, it is made up of two or more pieces of glass, of different types, designed to correct for aberrations such as chromatic aberration. To construct a visual refractor, a lens is placed beyond the images formed by the objective and viewed with the eye. To construct a photographic refractor or simply a camera, a photographic plate is placed at the position of the image. Simplified optical diagram of a refracting telescope. Refracting optical system used to photograph a star field. Generally, refracting telescopes are used in applications where great magnification is required, namely, in planetary studies and in astrometry, the measurement of star positions and motions. However, this practice is changing, and the traditional roles of refractors are being carried out effectively by a few reflecting telescopes, in part because of effective limitations on the size of refracting telescopes. A refractor lens must be relatively thin to avoid excessive absorption of light in the glass. On the other hand,the lens can be supported only around its edge and thus is subject to sagging distortions that change as the telescope is pointed from the horizon to the zenith; thus its thickness must be great enough to give it mechanical rigidity. An effective compromise between these two demands is extremely difficult, making larger refractors unfeasible. The largest refracting telescope is the 1-m (40-in.) telescope-built over a century ago-at Yerkes Observatory. This size is about the limit for optical glass lenses. REFLECTING TELESCOPES The principal optical element, or objective, of a reflecting telescope is a mirror. The mirror forms an image of a celestial object (Fig. 3) which is then examined with an eyepiece, photographed, or studied in some other manner. Viewing a star with a reflecting telescope. In this configuration, the observer may block the mirror unless it is a very large telescope. Reflecting telescopes generally do not suffer from the size limitations of refracting telescopes. The mirrors in these telescopes can be as thick as necessary and can be supported by mechanisms that prevent sagging and thus inhibit excessive distortion. In addition, mirror materials having vanishingly small expansion coefficients, together with ribbing techniques that allow rapid equalization of thermal gradients in a mirror, have eliminated the major thermal problems plaguing telescope mirrors. Some advanced reflecting telescopes use segmented mirrors, composed of many separate pieces. By using a second mirror (and even a third one, in some telescopes), the optical path in a reflector can be folded back on itself, permitting a long focal length to be attained with an instrument housed in a short tube. A short tube can be held by a smaller mounting system and can be housed in a smaller dome than a long-tube refractor. DERIVATIONS IN TELESCOPE Two fundamentally different types of telescopes exist; both are designed to aid in viewing distant objects, such as the planets in our Solar System. The refracting telescope uses a combination of lenses to form an image, and the reflecting telescope uses a curved mirror and a lens.The lens combination shown in Figure is that of a refracting telescope. Like the compound microscope, this telescope has an objective and an eyepiece. The two lenses are arranged so that the objective forms a real, inverted image of a distant object very near the focal point of the eyepiece. Because the object is essentially at infinity, this point at which I 1 forms is the focal point of the objective. The eyepiece then forms, at I 2, an enlarged, inverted image of the image at I 1. In order to provide the largest possible magnification, the image distance for the eyepiece is infinite. This means that the light rays exit the eyepiece lens parallel to the principal axis, and the image of the objective lens must form at the focal point of the eyepiece. Hence, the two lenses are separated by a distance fo + fe , which corresponds to the length of the telescope tube. The angular magnification of the telescope is given by à °Ã‚ Ã…“ ½/à °Ã‚ Ã…“ ½o, where à °Ã‚ Ã…“ ½o is the angle subtended by the object at the objective and à °Ã‚ Ã…“ ½ is the angle subtended by the final image at the viewers eye. Consider Figure, in which the object is a very great distance to the left of the figure. The angle à °Ã‚ Ã…“ ½o (to the left of the objective) subtended by the object at the objective is the same as the angle (to the right of the objective) subtended by the first image at the objective. Thus, tan à °Ã‚ Ã…“ ½o= à °Ã‚ Ã…“ ½o= -h/f o where the negative sign indicates that the image is inverted. The angle à °Ã‚ Ã…“ ½ subtended by the final image at the eye is the same as the angle that a ray coming from the tip of I1 and traveling parallel to the principal axis makes with the principal axis after it passes through the lens. Thus, tan à °Ã‚ Ã…“ ½=à °Ã‚ Ã…“ ½=h/fe We have not used a negative sign in this equation because the final image is not inverted; the object creating this final image I2 is I1, and both it and I2 point in the same direction. Hence, the angular magnification of the telescope can be expressed as m= à °Ã‚ Ã…“ ½/à °Ã‚ Ã…“ ½o=h/fe /-h/fo=-fo/fe and we see that the angular magnification of a telescope equals the ratio of the objective focal length to the eyepiece focal length. The negative sign indicates that the image is inverted.When we look through a telescope at such relatively nearby objects as the Moon and the planets, magnification is important. However, individual stars in our galaxy are so far away that they always appear as small points of light no matter how great the magnification. A large research telescope that is used to study very distant objects must have a great diameter to gather as much light as possible. It is difficult and expensive to manufacture large lenses for refracting telescopes. Another difficulty with large lenses is that their weight leads to sagging, which is an additional source of aberration. These problems can be partially overcome by replacing the objective with a concave mirror, which results in a reflecting telescope. Because light is reflected from the mirror and does not pass through a lens, the mirror can have rigid supports on the back side. Such supports eliminate the problem of sagging. Figure shows the design for a typical reflecting telescope. Incoming light rays pass down the barrel of the telescope and are reflected by a parabolic mirror at the base. These rays converge toward point A in the figure, where an image would be formed. However, before this image is formed, a small, flat mirror M reflects the light toward an opening in the side of the tube that passes into an eyepiece. This particular design is said to have a Newtonian focus because Newton developed it. Above figure shows such a telescope. Note that in the reflecting telescope the light never passes through glass (except through the small eyepiece). As a result, problems associated with chromatic aberration are virtually eliminated. The reflecting telescope can be made even shorter by orienting the flat mirror so that it reflects the light back toward the objective mirror and the light enters an eyepiece in a hole in the middle of the mirror. LIMITATIONS For many applications, the Earths atmosphere limits the effectiveness of larger telescopes. The most obvious deleterious effect is image scintillation and motion, collectively known as poor seeing. Atmospheric turbulence produces an extremely rapid motion of the image resulting in a smearing. On the very best nights at ideal observing sites, the image of a star will be spread out over a 0.25-arcsecond seeing disk; on an average night, the seeing disk may be between 0.5 and 2.0 arcseconds. It has been demonstrated that most of the air currents that cause poor seeing occur within the observatory buildings themselves. Substantial improvements in seeing have been achieved by modern design of observatory structures. The upper atmosphere glows faintly because of the constant influx of charged particles from the Sun. This airglow adds a background exposure or fog to photographic plates that depends on the length of the exposure and the speed (f/ratio) of the telescope. The combination of the finite size of the seeing disk of stars and the presence of airglow limits the telescopes ability to see faint objects. One solution is placing a large telescope in orbit above the atmosphere. In practice, the effects of air and light pollution outweigh those of airglow at most observatories in the United States.

“Medea” Aristotelian Analysis

Aristotelian Analysis – Music/Sound & Spectacle (Medea) V. Music/SoundThe Use of Sound in Medea Eurypides uses sound to great effect in Medea. Perhaps most prevalent is the fact that all the women are played by men, most likely talking and singing in a high pitched falsetto, giving the play a high, screeching tone, which would certainly put the audience on edge. This would add to the tension, and provide an exaggerated contrast between the men, speaking in their natural voices, and the women in their falsetto.This also influences the musical nature of the play. As compared to other Greek tragedies where the chorus would have been intentionally all male, Medea would have a very different sound, a much more feminine sound, as would be fitting for one of the few Greek plays with a female protagonist. The language Eurypides uses helps the audience understand her and her actions, as well as be able to empathize with her. Words of destruction, such as â€Å"kill,† â€Å"brok en,† â€Å"refugee,† â€Å"sick,† â€Å"hate,† â€Å"enraged,† and â€Å"starves† all set the stage in the first 20 lines of the play.The audience instantly knows that Medea has suffered horribly, and now has every right and reason to take revenge for the wrongs that have been done to her. These same words are used often throughout the play, especially â€Å"hate† and â€Å"betrayed† and give us great insight into the total fury and single mindedness of Medeas later actions. Jason's words, on the other hand, help us realize just how disconnected he is. He is, as the Chorus says â€Å"ignorant beyond pity. †Ã‚   Jason thinks he is being â€Å"generous,† and he somehow thinks leaving his wife for a younger woman makes him her â€Å"advocate. Eurypides carefully emphasizes the scene where the children are slaughtered by having it be the only time we hear them speak. They are on stage for many scenes, but they never d o anything but watch, silent and obedient while their family falls apart around them. When they finally speak, it is because it is their only hope of saving themselves; it is too late for their family. They cry out, with young innocent voices, pleading for help in what is perhaps the most tense moment of the play.This tension is further heightened by the fact that the audience cannot see what is happening, they can only hear it. They are forced to rely on sound alone, and that sound for those few lines becomes the only thing that matters. One almost wants to watch Medea kill her children just to know what is actually happening behind that door instead of being denied perhaps our most important sense: sight. The audience becomes blind to the action of the play, as Medea has embraced her blind rage. Social Implications:In the last lines of Medea, Euripides uses the verbal interaction between Jason and Medea to show a reversal in the stereotypical gender roles of the time. Although Med ea is a goddess, she represents a strong, unyielding female role that has power over her male counterpart in their relationship. Moments before the final grand spectacle, a distraught, weakened Jason is powerless to the will of Medea. He raises his voice (indicative of his losing all authority and pathetically lashing out for some form control) and demands that he be allowed to have his children back.Yet Madea is unwavering and persistent. Unlike Jason, she â€Å"wastes† no words and provides a simple, rational-sounding message that reflects her supremacy. This kind of social commentary is interesting because women, who were rarely awarded the liberties of men at the time, were allowed to attend the plays at the Dionysus festival. It is possible that Euripides was sending a subtle message of hope and pride to all of the oppressed female members of his audience. Dialect:Euripides was celebrated for his simplistic use of language which reflects a more realistic dialogue in the character's expressions. Although he did not win as many first place awards as Sophocles or Aeschylus at the Dionysus festivals, his work was popular to an audience which was able to recognize their own dialects and accents on stage. Unlike other tragedies of his time, Euripides's work was not diluted by unrealistic, grandiose phraseology which often had a deleterious effect on the listener's comprehension and ability to interprate the plays.Physical Realities of Sound in Ancient Greek Theater: Ancient Greek theaters were specially constructed to perfectly suit the art which they housed (although without roofs). The multi-thousand-seat theaters were built into hilsides to allow for minimal construction and also excellent accoustics. In today's theater, sound is almost always electronically amplified to permit better hearing by the audience, but not having this as an option, these grecian temples had to be constructed perfectly.By encircling the orchestra   with a mathematically pe rfected design of wooden or stone benches, sloping upwards away from the performance, the ancient architects nearly mimiced the way that sound travels as it spreads. This near-perfect acoustical environment allowed the actors' voices to travel all the way to the last row of seats. Also, the Skene buidling which stood behind the orchestra may have assisted in the amplification by reflecting voices and sound towards the thousands of audience members.This arrangement meant that the words which were spoken and sounds of music and dancing were clear such that their importance could be heard accurately. The theaters of Ancient Greece enormous, when, for example, the nearest seat was almost 10 meters away from the performer, large movements and loud voices were critical to conveying the full story. As such, it is widely accepted that the performers would wear very simple, plain masks which made their facial features more clear and obvious for the audience to see.Some theater historians ass ert that these masks also had a type of megaphone built in for amplification, although this point is disputed. In conjunction with their enlarged faces, the performers were often on stilts and wearing heavy robes of fabric to accurately convey their character. These amendments to their body meant that every move they made and every sound they created needed to be worth it. There was no â€Å"stage whispering† in this theater which limited but also inspired Euripides to write plays with more dynamic and complex plotlines, ones filled with action and confrontation to futher add to the experience.In addition, the chorus of some twelve men (playing women in Medea) would constantly dance around the orchestra (derived from the Greek term for dancing) during their scenes. The dancing was entertaining but also allowed the group to spread around the wealth so to speak of their odes, so that all might be privy to hearing their sound and seeing their dance. VI. Spectacle The Greatest Sp ectacle: After the extraordinary hardships which Medea faces throughout the play, we come across the ending when she â€Å"appears in a winged chariot, rising above the house. The bodies of the two children are visible in the chariot. Interestingly, over the past 1570 lines of the play, the stage directions are almost never this specific or elaborate. Showing that Euripides has literally saved the best for last, perhaps to shamelessly present a big ending, the rising chariot is the epitome of spectacle in this play. Although there would be no such chariot in the ancient theaters, it is likely that Medea herself would be lifted from the stage level by the deus ex machina (literally, god machine) and the childen's bodies would be thrust forth on a rolling wagon from the skene in the rear of the orchestra.By creating such a spectacle, Euripides also highlights the importance of this event: Medea has killed her own childen in order to free them from the terror of the world which has be en created for them. Her actions display her insanity, and her relentless pursuit of revenge against Jason. Setting and Costumes: The unique Greek theaters which seated many thousands called for very simplistic yet very clear design choices. Instead of elaborate costumes, the performers would wear large bold costumes which allowed even the farthest spectator to be clear on who is who.Due to the widely acknowledged â€Å"three-actor rule† (whereby three actors played the roles of all the characters in a play) the costume and mask changes would need to immediately reflect differing characters. It is also widely accepted that the performers would wear a type of stilts to make them â€Å"larger than life† leading to two interpretations: the actors could be better seen and heard when higher, but also became almost godlike or unrealistically large- adding to the spectacle of this world. Entrances and Exits:In the rear of the orchestra section was the Skene, a large building which served as a universal setting for Greek Theater. The sometimes elaborate building would generally have a major door in the center (for palace settings) as well as machines which hoisted actors above the orchestra section. Some characters may have entered this way, but most, including the chorus, would enter on ramps adjacent to the orchestra area. These eisodoi or parodoi would be used for entrances by characters such as a messenger or soldier. How did the actors move:Simply, the actors moved in large, overstated motions. In order to make the play as clear as possible for the large audiences, subtlety was not an option for the ancient Greeks. But what this also meant   for the performance was that the plot had to be appropriately planned for this style of acting. Performers carried out sometimes-long speeches with highly clear emotional intent. This style is a crucial part of Medea. As the plot continues and Medea's situation worsens, emotions become increasingly polar and d isjointed, making clear the protagonist and antagonist's intentions.

Developing the Global Dimension in Schools and in Classrooms Essay

The School The school where I carried out the research for my report is St Augustine of Canterbury Roman Catholic High School in Oldham. The pupils come from a wide variety of backgrounds including English and Irish working class, Pakistani, Indian, Black Caribbean, Black African, Travellers, Polish and pupils who are of mixed race. The religions I encountered included Roman Catholic, other Christian, Muslim and Hindu. Many of the Pupils at St Augustine’s have very limited experience of the outside world due to the poorer backgrounds that they come from. The Lessons This report is based on a series of four lessons I taught to a Year 11 Citizenship class. The topic of the lesson is the continent of Africa, problems within the continent, possible solutions to the problems and their complications. The purpose of the lessons is also to create a sense of empathy in the pupils, improve their research skills, and give them the opportunity to present their findings at the end of the unit. In the first lesson, the pupils are given a map of Africa and a list of countries. They have to use the internet to find out where the countries are situated on the map. This provokes discussion over how countries in Africa were formed and how their borders were affected by Western Colonisation and the World Wars. The second part of the lesson involves a brief discussion over some of the well known problems in Africa such as Civil War, Corruption, HIV, Poverty and Famine after which the pupils will start their own powerpoint presentation describing these. The pupils are assisted in starting this with fact sheets on HIV and AIDS in Africa and on Corruption in Africa. The second lesson focuses on Civil War in Africa. The pupils are given worksheets with the names of four countries that have faced Civil War, Rwanda, Ethiopia, Sudan and Sierra Leone and questions on the impact of war in these countries. The pupils watch a trailer for the film Hotel Rwanda which focuses on the Rwandan Genocide. There is discussion on what they have seen, which expands into related topics such as refugees before they are allowed to go on the internet and research the answers to the questions for two of the countries. The second half of the lesson is spent working on the powerpoint presentations and adding some of the facts they have researched into their own presentation. The third lesson focuses on Fairtrade in Africa. The pupils are given a worksheet asking questions about Fairtrade and shown a short video on the projector promoting and explaining what Fairtrade does for African producers. The pupils are directed to the Fairtrade website in order to answer any remaining questions on their sheet. The second half of the lesson is spent finishing off their powerpoint presentations and adding facts about Fairtrade. In the fourth lesson, the pupils present their findings to the rest of the class and discuss the issues as a class, each having the opportunity to express their opinions on the topic and the different aspects they have covered. The Focus Group What did pupils learn from the lesson and how do they feel school prepares them to be part of an ethnically and religiously diverse society? I chose 4 pupils to take part in my focus group, Jodie who was very opinionated, from a white, working class background; Priya, a Hindu, Indian girl who was more quiet but got caught up in the debate; John who is from a mixed Black Caribbean and White background; and Mlala, a boy from a West African background. Jodie felt very resentful about being â€Å"forced to take Citizenship†. She felt it was a waste of time as there is no qualification or exam to sit in this subject. She felt it was a waste of time and she had very little interest in what happened in Africa, she felt it would be more relevant to study problems occurring in the UK during Citizenship lessons. During the class discussions she was unsympathetic to the plight of refugees and had strong feelings regarding their presence in the UK and on immigration as a whole. John was of a similar opinion, he thought that Africans should â€Å"sort out their own problems†. Priya defended refugees and their need to come to this country pointing out that it is not always possible for refugees to go to the next nearest country as there may be trouble within that country as well and that if there are a lot of refugees coming from countries that are close to each other that one or two countries that are stable enough to accept refugees cannot take all of the refugees. Mlala also pointed out that some of the problems that occur in Africa are a direct result of European colonisation and war. I understand why Priya and Mlala are more reluctant to get involved in the debate. To some extent they may feel that the comments are directed at them or their friends or families. They see the issues of developing countries from a different perspective. Mlala only came to the UK in the last year and has grown up in West Africa. He and his family are immigrants themselves, he dislikes the picture painted in the media but does not want to get into direct confrontation over it. Priya was born here but has strong roots in India; she has friends and family there who she visits and who have come to live in the UK more recently. I also understand where these feelings are coming from in Jodie and John in the sense that they are growing up in working class, white households which are targeted in the media to feel that immigrants and refugees are coming to the UK and making life more difficult for them affecting housing, jobs, schooling the NHS and opinions within their families are being reflected through them. Jodie and John did appear to enjoy having the opportunity to express their opinions about issues that are highlighted in the media and discussed at home. Priya and Mlala, were more reluctant to talk about the issue, I believe they may have felt uncomfortable at times about some of the issues raised and the strength of other peoples opinions, however as the debate went on they were motivated to speak to get across their own different points of view. My Reflections I felt at the end of the lessons and the focus group that something had been achieved in the sense that Jodie and John’s opinions appeared to soften and they had learned some facts that they were previously unaware of. Priya and Mlala, I hope came out of it mor confident for speaking their minds and making their opinions known. I feel that the lessons were a success in the sense that they created a framework for debate and got the pupils thinking about these issues instead of just accepting what they read in the Tabloids and hear from the people around them. When I prepared the lessons I had to stick within the framework of the the topic for problems within Africa but I feel it would be good to have the opportunity to use the topic of Africa to challenge peoples’ preconceptions of the continent and the people, perhaps by focussing on the more positive aspects of Africa in order to give the pupils a more balanced viewpoint.

The Basic Properties Of Stem Cells - 1937 Words

The first authoritative source I used was the National Institutes of Health website. This site had various pages explaining what stem cells are, the different types, what they can be used for, when they will be able to be used, and where more information can be found. The site explains stem cells as being distinguishable from other cells in two ways. They are unspecialized cells capable of regeneration through cell division, and they can form different organ- and tissue- specific cells under certain conditions. After explaining the basic properties of stem cells they explain the three types of stem cells and what makes them different. Embryonic stem cells are collected from embryos that are formed through in vitro fertilization. These embryos have to donated from donors that have been given consent in order to use them for research. The website explains, in detail, how these embryos are created in a lab. It also explains how the cells can be manipulated to form the desired mature cel l product. This can be done through three techniques, â€Å"change the chemical composition of the culture medium, alter the surface of the culture dish, or modify the cells by inserting specific genes.† Adult stem cells, also known as somatic stem cells, are found in different tissues of the body. Their role is to stay dormant in a tissue until there is a need for it to divide and specialize in order to repair or maintain that tissue. There are a variety of somatic stem cells. They areShow MoreRelatedThe Debate Over Stem Cell Research1027 Words   |  5 PagesStem cell research is the study of basic cells that are grown in laboratories where tests are made to determine the essential properties of the cells. Over the past few decades, stem cell research has become a popular scientific debate and controversy. 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