SENSE OF SIGHT….
The eyes are sensory organs. They keep the brain updated with information about is what happening around the body. Both contain millions of tiny sensors that send messages along nerves to the brain. Sensors in the eyes respond to light and, through the brain, let us see the world. Sensors in the skin respond to touch and allows us to feel. *
The seeing eye…
Light enters the eye through the clear cornea. It then passes through the pupil and is focused by the lens on the retina. This thin layer covers the back of the eye and contains cells that are sensitive to light. When light hits the cells, they send signals to the brain. There, the signals are turned into pictures so we can see.
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light). The first known practical telescopes were invented in the Netherlands at the beginning of the 17th century, using glass lenses. They found use in terrestrial applications and astronomy.Within a few decades, the reflecting telescope was invented, which used mirrors. In the 20th century many new types of telescopes were invented,
including radio telescopes in the 1930s and infrared telescopes in the 1960s. The word telescope now refers to a wide range of instruments detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.
The earliest recorded working telescopes were the refracting telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals: Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, and Jacob Metius of Alkmaar. Galileo heard about the Dutch telescope in June 1609, built his own within a month, and greatly improved upon the design in the following year.
The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs and several attempts to build reflecting telescopes. In 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector.The invention of the achromatic lens in 1733 partially corrected color aberrations present in the simple lens and
enabled the construction of shorter, more functional refracting telescopes. Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century—a problem alleviated by the introduction of silver coated glass mirrors in 1857, and aluminized mirrors in 1932. The maximum physical size limit for refracting telescopes is about 1 meter (40 inches), dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been
reflectors. The largest reflecting telescopes currently have objectives larger than 10 m (33 feet).The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937. Since then, a tremendous variety of complex astronomical instruments have been developed.
How to use…
* Find an area where the items you wish to view aren't obstructed by trees to set up your telescope so that you get a clear view of the sky.
* Look to see if your telescope has a polar axis. If it does, it will track whatever you are looking at. If you have a telescope with a polar axis, follow your manufacturer's directions on how to align the polar axis and...
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