The Kings Astronomer

The discovery of the new planet made Herschel an instant celebrity. He named the planet Georgium Sidus, in honor of King George

Telescope Building at Home

It is quite possible to build a telescope at home today. It is not difficult, yet it does take some patience. Looking at the stars and planets through a device created by oneself is a true pleasure, and anyone with the time and a little spending money can do it. Kits from hobby stores provide most of the materials needed to begin a telescope-building project, and the prices vary depending on the size of telescope one wants. The most popular size for the beginner is the six-inch (15 cm) reflecting telescope. "Six inches" refers to the diameter of the mirror, not the length of the tube.

An important part of telescope creation is in the grinding of the mirror. Like most worthwhile things, precision accuracy can be accomplished with practice using simple equipment and one's own two hands. All that is needed for grinding is a solid support stand at about waist level, water, grinding abrasive, and two glass discs, one of which is called the mirror blank and the other, the tool.

Placing the blank atop the tool, with the center of the blank near the edge of the tool and a wet abrasive in between, one begins to grind by rubbing the two together in a circular motion while also walking around the stand to insure uniformity. As one does this, the top blank will become concave and the bottom tool will become convex. As work progresses, finer and finer abrasive powder is used, making the surface increasingly smoother. Examples of some abrasives are silicone carbide, emery, and aluminum oxide. Upon completion, the surfaces will be highly reflective. Many hours of grinding and changing grit from coarse to fine are required to prepare a mirror surface. Simple tests on reflectivity and focal length can be achieved by using an ordinary lightbulb or sunlight and some glycerin.

III, and the name remained such all of Herschel's life. (In 1850 it was officially renamed Uranus, after the father of Saturn—a fitting new name since Saturn was the father of Jupiter and Jupiter was the father of Mars, in that order.) Due to his discovery, in 1781 Herschel became a member of the Royal Society of London.

King George III heard of Herschel's achievement and summoned him to court. Duly impressed, the king offered Herschel a position as royal astronomer with a salary of £200 a year. This enabled Herschel to end his musical career and devote all of his time to astronomy. In time, Caroline was also employed, earning £50 a year as assistant to the new royal astronomer. In 1782, they both moved to Datchet, Berkshire, to begin their new roles in astronomy. By 1784, William Herschel had compiled a catalog of 800 double stars, arriving at the conclusion that many were not double stars at all, but were in fact binary stars, which are two stars that rotate around a common center of mass. Double stars are two stars that appear close in the sky but have no physical connection. Herschel's conclusion of the motion of binary stars was the first hard evidence in support of Newton's universal law of gravitation (named for Sir Isaac Newton, who first proposed such a law in 1687).

Herschel also went to work on plans for a bigger, 30-foot (9 m) telescope, but his plans were canceled. The metal cast for the mirror would have weighed 500 pounds (227 kg)! It was not something easily handled, and he did not have the means to do it. This did not stop him. In 1786, after he and Caroline moved to Slough, where observing was better, Herschel announced a plan to construct a great 40-foot (12.2 m) telescope with a 48-inch (122 cm) mirror. King George backed him with the necessary financing and labor. For the grinding of such an enormous mirror, Herschel designed a special device.

By 1787, while still working on his 48-inch telescope, Herschel discovered two moons orbiting Uranus, using another telescope of his creation, a 20-inch (61 cm) reflecting telescope. In 1788, he married the widow of a wealthy merchant, Mary Baldwin Pitt. Together they had a son, John Frederick William Herschel (1792-1871), who also became an astronomer. The moons of Uranus were later given names by his son John: Titania and Oberon.

The great telescope was finished in 1789 and erected inside a huge wooden framework. Herschel's telescopes strayed from the common design of the Newtonian reflecting telescope (developed

HERSCHEL'S GREAT TELESCOPE

Mirror

Herschel constructed the most magnificent telescope in the world during his time. The device was 40 feet (12.2 m) long with a 48-inch (122 cm) mirror. He stood on a scaffold near the lip of the telescope in order to see into the eyepiece.

by Isaac Newton in 1668) because the primary mirror was slanted in a way that threw the image to the side, where it could be viewed near the lip of the opening. This design was called the Herschelian telescope, and it required no secondary mirror, which meant less grinding. Unfortunately, for viewing to take place, Herschel had to climb a scaffold high off the ground in order to look into the top of the instrument. Though Herschel's mirror design was unique, large telescopes were common, and more than a few persons were known to have fallen from the framework while observing the night sky.

Through the new great telescope, he at once discovered two new moons of Saturn, bringing its number of moons up to seven. With some dismay, however, Herschel found that the best instrument of his creation was his smaller 20-inch telescope and the cumbersome, 40-foot instrument was used only seldom. The drawback to all Herschel's (and most other) telescopes was the constant need to remove the metal mirrors and polish away the tarnish. This time-consuming task was also done more quickly and easily with the smaller telescope.

Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

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