The Scientific American Book of Great Science Fair Projects


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Full Name Comment goes here. Are you sure you want to Yes No. Don't lose your Ex girlfriend! This weird trick will get her back! Show More. No Downloads. Views Total views. Actions Shares. Embeds 0 No embeds. No notes for slide. A few bxigs remain in this pilot model. The oscilloscope shows some highly unconventional and mysterious wave forms here and there. Other builders will doubtless find ways to improve the circuit, and I will welcome a report of their results.

But the bugs have no discernablc effect on the operation of the unit. Operation in the field is simplicity itself. Set up the telescope, plug in the cords, adjust the speed and you are ready to observe. It is assumed that amateurs who undertake the construction of this device will have some experience with electronic circuits. Others are urged to solicit the cooperation of a neighboring radio "ham. Similar booklets covering equivalent transistors made by other manufac- turers are available through most radio dealers.

The quotient gives the smallest angular separation, in seconds of arc, at which two equal- ly bright point sources of light can be distinguished.


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Any pair sep- arated by a smaller angle will merge because of the wave nature of light and be seen as a single point. Hence if the performance of the huge telescopes were limited only by their optical quality, they would indeed give breathtaking views of the planets. Although the big instruments arc virtually perfect in their op- tical and mechanical construction, and have surpassed their ex- pected performance in the applications for which they were de- signed, there is very little likelihood that they will ever show planetary detail to the limit of their theoretical capabilities.

In fact, there is good reason to believe that the best planetary and lunar photographs will be made with telescopes of but 30 to 40 inches aperture.

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Again, the ring sys- tem of Saturn has never been adequately photographed. Most photographs show only the two main rings and the largest divi- sion, whereas the faint crape ring is very clear visually in small telescopes, and at least two other divisions are recognized. The canals of Mars may be a third example. Their failure to appear on any of the many thousands of photographs that have been made of this planet is the cause of a long-standing controversy regard- ing their existence.

Many qualified observers have reported seeing them. Others, apparently equally qualified, sec not a trace of them. Even a single convincing photograph could settle the ques- tion of their existence. These examples, particularly that of the lunar craters, clearly establish that a wide gap exists between well-subs tan tiat id visual observation and the corresponding photographic results. The degree of optical steadiness of the atmosphere is called the "seeing. Neighboring rays interfere with one another and cause the observed color and brightness changes.

In times of good seeing the atmosphere is relatively calm and thermally uniform and there is little or no naked-eye stellar scintillation. During bad seeing, on the contrary, the atmosphere is quite nonuniform thermally and a large degree of scintillation is visible.

The Scientific American Book of Great Science Fair Projects

It may be created by local warm objects such as motors, vacuum tubes or observers near the telescope itself , by a difference in temperature between the telescope tube and the surrounding air, or by nearby chimneys or factories which emit heat. More basically, the inhomogeneities are caused by large-scale convection currents which accompany cloud forma- tion and thunderstorms, or by turbulence between atmospheric layers having different temperatures and wind velocities.

The character of the seeing ean be viewed telescopically in con- siderable detail by observing an out-of-focus image of a bright star.

The pattern you see resembles the bands and spots of sun- light on the bottom of a slightly agitated pool of water. They are in eonstant motion.

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Slow-moving patterns with sharp boundaries generally signify nearby heat sources, and these can often be tracked down by careful observation. This re- fers to the size of the region over which the air temperature is sufficiently uniform so tliat a parallel light beam passing through such a region to the telescope is negligibly distorted. The part of the objective that receives such a beam forms a perfect image.

If the eell size is substantially smaller than the telescope aperture, the objective will encompass several such cells, with the result that a number of separate images are formed by the telescope. These then combine to form a blurred image on which fine detail cannot be resolved. If only a few such cells cover the aperture, the sep- arate images may be individually visible. Each star or other object is split into a small cluster. This is often the ease with fine detail such as the craters of the moon or the Jovian satellites.

At the other extreme the seeing cell size may be much larger than the telescope aperture, so that the entire objective acts as a unit and the resultant image is clear and sharp. But the image will move irregularly about some average position. Un- der given conditions of seeing it is clearly disadvantageous to use an aperture larger than the seeing cell-size. This aperture will yield a brighter image, though it will show less detail. What is the best size of telescope, then, for visual observation?

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It ought to be large enough to take advantage of the best seeing ie. The maxi- mum size thus depends upon the geographical location, for at each location there is a certain distribution of seeing conditions through- out the year, and on each night there is a corresponding maximum useful aperture for visual observation. On most nights, even at a favorable location, this will be less than three or four inches. On many it may be as large as 10 or 12 inches.

But apertures as large as 50 or 60 inches very seldom can be used with maximum effect. The greatest telescopes, such as the incli and inch re- flectors, will encounter seeing conditions fully matching their aper- tures only once in many years. Indeed, no astronomer who has used the inch Hale telescope has yet reported star images less than about tlirce tenths of a second of arc in diameter.

Obviously a visual observer gains no advantage at the eye- piece of tlie huge telescopes. If wc now consider the photographic situation, a new element enters the problem. This is the requirennent that a sufficient ex- posure time be provided to yiedd a satisfactory photographic image. Because of this tlie advantage of a smaller aperture disap- pears, since the fainter image corresponding to the smaller aper- ture requires a longer exposure and will therefore move about more on the film, yielding a blurred image.

Tims for pliotograpliic purposes it is almost immaterial whether a large or small aperture is used, so long as it is at least as large as the seeing conditions will permit for visual observation. It should now be clear why direct vision has proved superior to photography for the observation of lunar and planetary detail. For photographic observation, on the contrary, it is quite neces- sary that the image be both sharply defined and steady for the dura- tion of an exposure. Furthermore, a visual observer has a great advantage in being able to ignore the times when the image is distorted and to remember the moments when it is excellent, while the photographic plate indiscriminately records all the accumu- lated fluctuations.

Yet in spite of the marvelous ability of the eye to catch, and the brain to retain, fleeting glimpses of extraordinarily fine detail, we cannot regard the situation as anything but unsatisfactory. The eye is not a quantitative measuring instrument, and the brain is not always objective in what it records. The accuracy, objectivity and permanence of the photographic record arc as much to be desired here as in other fields of science. A number of possibilities exist for removing or relaxing the limitations that the turbulent atmosphere imposes on stellar pho- tography, The most obvious of these is to try to exploit those very rare nights when a large telescope actually will perform better than a small one.

Unfortunately this requires more than a steady atmosphere; it also lequires that a suitable object be available in a favorable location to photograph. In the case of the moon, this immediately reduces the likelihood of such a coincidence by at least a factor of four, and in the ease of Mars, by a factor of at least 40, not allowing for the fact that the most favorable opposi- tions of Mars occur when it is low in the sky for the majority of the large telescopes in the world. It would be the sheerest accident if any ordinary photograph of Mars taken with the inch tele- scope within the next century were to show detail worthy of its tremendous resolving power!

In contrast with the performance of the inch, the chances of good seeing improve so rapidly with diminishing aperture that a telescope of 40 or 50 inches might be used effectively for plan- etary photography, provided photographs were taken almost con- tinuously during every reasonably steady night. But this would require reserving a large portion of the observing time for such use. Such a program probably could not be justified except pos- 3! Clearly the economic justification of the big telescope does not lie in its ability to resolve minute details of bright, relatively close objects.

Rather, its immense light-gathering power is largely ex- ploited for photographing objects too faint or remote in space for smaller instruments. We cannot hope to take the much-desired photograph of Mars by the mere expedient of building ever more powerful telescopes. How, then, may we approach the job? Although no ideal solution is known at present, several possibil- ities have been suggested and some have been tried with promis- ing results.

One is to remove directly the main cause of the problem: the atmosphere. This could be done by taking the tele- scope away from its traditional bedrock foundation and lifting it above most of tlie atmosphere in a rocket, a balloon or a high- altitude jet aircraft. A different line of attack, whicli sliows considerable promise, involves the use of electronic image intcmsification.

The aim here is to reduce the required exposure time so drastically that the image from a relatively small telescope could be utilized. A sys- tem based on this principle has been tested at thci Lowell Observ- atory at Flagstaff, Ariz. It yields enough intensification to permit a fold reduction in exposure time.

Tho image thus has less time for wandering about on the film, and smearing is reduced accord- ingly. This is essentially a closed-circuit television system utilizing an image-orthicon pickup tube connected through an amplifier to a picture tube. The picture tube is then photographed with a cam- era whose shutter is suitably synchronized with the picture. With this method the possibility also exists of defecting electronically the moments when the image is sharpest and building up a com- plete exposure out of many selected shorter intervals.

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It is too early to evaluate the capabilities of the new electronic methods, but doubtless much will be heard of them in the future. During the past few years I have experimented with a third approach in which an electronic guiding system is used to cancel out most of the motion of the image on the film. This motion is erratic, but the image remains within one or two seconds of arc of some aver- age position.

Most important, the image moves slowly enough so that the design of an electromechanical servo system capable of following it appeared practicable. After the usual number of false starts, I assembled a guiding; device and tested it on an artificial planet in the form of an illu- minated hole two millimeters in diameter in a metal sheet.

The Scientific American Book of Great Science Fair Projects The Scientific American Book of Great Science Fair Projects
The Scientific American Book of Great Science Fair Projects The Scientific American Book of Great Science Fair Projects
The Scientific American Book of Great Science Fair Projects The Scientific American Book of Great Science Fair Projects
The Scientific American Book of Great Science Fair Projects The Scientific American Book of Great Science Fair Projects
The Scientific American Book of Great Science Fair Projects The Scientific American Book of Great Science Fair Projects
The Scientific American Book of Great Science Fair Projects The Scientific American Book of Great Science Fair Projects

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