Credit for the first reflector goes to an Italian professor named Niccolo Zucchi. He made his first scope in 1616 but the design of his scopes was not very practical. James Gregory was a Scottish Mathematician and Astronomer of the 17th Century and he is credited with having designed the first practical reflector telescope. In 1663 he published this design in his book titled Optica Promota. But he didn’t build the first working model until ten years later with the help of scientist Robert Hooke. It was in this ten year period that Sir Isaac Newton built his famous Newtonian telescope (1670). So the Gregorian telescope predates the Newtonian in design but Newton’s was the first to be built.

How the Gregorian Telescope works

To understand how the Gregorian reflector works we will first take a look at the Newtonian telescope. In the Newtonian a parabolic mirror placed at the bottom of a tube and it focuses light back up the tube to a flat mirror that directs it out the side of the tube to an eyepiece.  The eyepiece is on the side of the tube. In a Gregorian design the parabolic mirror is at the bottom of the tube and it focuses light back up the tube but the second mirror is an ellipsoid and it redirects the light back down the tube to the eyepiece through a hole in the center of the large primary mirror. This type of telescope has the eyepiece at the bottom.

The benefits and shortcomings

Newton’s telescope has one parabolic mirror and one flat mirror while Gregory’s has a parabolic as its primary mirror and an ellipsoid as its secondary. Additionally, Gregory’s primary mirror needed a hole cut in the center of it. These things mean it is a much more optically complex instrument and much more difficult to make. Newton’s design is much easier to make.  This is probably why it took Gregory ten years to make his first working model.

The Gregorian does have some benefits over the Newtonian style scope. The ellipsoid secondary mirror is placed at a point after the focus of the light. This configuration, in conjunction with an eyepiece, provides an erect or right side up image while the Newtonian telescope gives an upside down image. This is a big benefit if you are using the telescope for terrestrial viewing.  And because of this inversion of image after the secondary mirror it allows a baffle to be placed inside the tube. This baffle prevents unwanted light and heat from reaching the primary mirror. This is a very useful tool when a telescope is meant to be used for solar observations where heat is a big concern. For this reason the Gregorian design is sometimes still used for telescopes that will be used for solar observations.

The Gregorian design for a telescope is not used very often in modern times. It has been changed and much improved by the Cassegrain telescope. But the Gregorian does find limited use occasionally as a finder scope that accompanies a larger scope. This is because of the nature of it displaying properly oriented erect images.  And because of its ability to have a baffle inside it is also sometimes used for telescopes built for solar observations.

Gregory’s telescope design is not much used in modern times but it was the forerunner and inspiration for many of today’s telescope designs.

 

The Gregorian Telescope – the First Practical Reflector is a post from: Meade Telescopes

First and foremost, there are three basic types of telescopes: reflector, refractor, and combo catadioptric.

· The reflecting telescope (or Newtonian) basically uses a concave design and mirror lens to reflect light off an object in the distance, to perceive it more closely. These types offer great light-gathering technologies, are typically stationary, and are the least expensive of the three. They are the best beginner telescopes for those interested in casually exploring the night sky at a value price.

· The refractor telescope works by using a number of lenses to refract or bend the light that is being transmitted by a distant object, to gain a more focused magnification from the eyepiece. Refracting telescopes are comparatively much more expensive; but also offer sharper, high-contrast, accurate views of the stars, planets, and moon above. It is also worthy to note that another bonus of the refractor is that it performs with aplomb in all atmospheric conditions, unlike the former.

· Lastly, is the catadioptric (example: matsutov-cassegrain) telescope. This type compasses both the bent lens system of the refractor telescope, as well as the mirror technology of the reflector telescope. Middle ground of all three, the catadipotric boasts high-quality precision, resolute optical technologies, convenient portability, and promises a more digestible price range than the refractor models.

Once decided upon what type of telescope you'd like to invest in; the next step is figuring out what technical specifications to look for, as far as magnification, aperture width, focal length, resolution, etc.

· Magnification is the first number listed in the formula usually expressed for a telescope, example: 100X5. The magnification in a 100X5 would be 100, and means that this telescope will give you 100 times the magnification you would perceive an object with than the naked eye. It is necessary to recognize that more is not always better, because the more the object is magnified, the less light is allowed to view it with.

· Aperture is the second number denoted by the formula (In this case: the 5, of the example 100X5), and is simply the diameter of the objective lens. The aperture measurement tells us how much light will be allowed in offering clarity to the object you are looking at. The larger the diameter, the more light allowed; and so it is necessary to adequately balance magnification (power) with appropriate aperture.

· Focal length (represented in millimeters) is the length that light has to travel within your telescope to reflect and perceive the object. The higher the focal length measurement: the higher the magnification, the larger the image, and the smaller the field of view.

· Resolution is the telescope's capability to render the object's image in detail. The higher the resolution, the sharper the details you will be able to perceive. This is directly in relation to the aperture width, as discussed earlier: the larger the aperture, the better the resolution.

Once you recognize the different types of telescopes, and the relationship of the basic specifications as listed above; you can begin to maneuver your way around selecting one for yourself. How casual your intended use, what objects you'd like to view, and how much you'd want to invest; all play a big part in determining the best telescope for your uses; but now armed with the basics of buying a telescope, you're sure to find the perfect new optical device with ease.

Buying A Telescope: Tips For First Timers is a post from: Meade Telescopes

The word astronomy is comprised of two Greek words. The Greek word astro means star shaped or star and pertains to outer space. The word onomy literally means the study of. Therefore, astronomy is the study of the stars.

One of the major tools that assists amateur and professional astronomers in understanding and respecting the galaxy is the astronomy telescope. When looking to purchase a good astronomy telescope there are a number of factors that you can keep in mind. First, of all consider some practical suggestions, remember it is about the diameter of the lens, and make sure your telescope has a solid stand.

Practical Suggestions

Before you purchase your astronomy telescope it is important to conduct your research. One way of conducting this research can be accomplished by accessing the Internet and learning more about telescopes. Some of the questions that you should endeavor to answer surround what features to look for in a telescope, approximate cost, recommended brands, etc.

Another practical suggestion, before you purchase your astronomy telescope, is to "test drive" a telescope. This can be accomplished by joining an astronomy club. Often these clubs will have a stargazing event which will allow you to peer through the telescopes owned by the various members.

Another way of conducting research, prior to purchasing an astronomy telescope, is to ask the members in the club as to what telescope they would recommend. The key is education. Listen for the features they recommend, brand names, the diameter of the lens, price, etc.

Also, you may come across a member of the club who is considering the purchase of a new telescope. If so, you may be able to purchase their used telescope.

Diameter Of The Lens

When considering the purchase of an astronomy telescope it is important to remember what is the key feature surrounding your purchase. That key feature should focus on the diameter of the lens of the telescope and not its advertised magnification.

This is because the diameter of the lens equates to the amount of light that can be received by the telescope. Therefore, the larger the diameter of the lens the more light that is captured. This in turn allows for the image that you are viewing to become more visible.

Solid Base

Another very important feature when considering the purchase of your astronomy telescope is to ensure that it has a solid base. Generally, these bases or mounts are tripods.

It is important that when the telescope is mounted on these bases that the telescope does not shake or move. Obviously, any movement by the telescope, when peering into space, will distort the image being viewed and provide a negative experience.

Buying Your First Astronomy Telescope is a post from: Meade Telescopes

When two lenses are combined together, they are able to collect more light than individual lenses. This is the main principle behind Galileo’s telescope. Most of the telescopes in use today, use the same principle. The human eye also works on a similar principle, but cannot collect too much light. Telescopes are able to gather more light because of the double lenses used in its construction. These lenses gather light and build an image by focusing the light at a point. Refraction is the mechanism in use to form such images. As a result, telescopes are also called refracting telescopes or refractors. The phenomenon by which the collected light bends and forms images is known as refraction.

Images were magnified by a factor of 30 in Galileo's invention. However, the shape of the lenses he used was such that his image became blurred and distorted. But no one had ever invented something so exciting with which to observe the night skies before Galileo's telescope. Galileo used his telescope to view the moon and observe it closely. He was also the one to figure out that the magnification factor of a telescope was provided by the ratio of the power of the concave lens to the power of the convex lens. So he premised that the simplest way to increase this magnification factor was to use a high power concave lens with a weaker convex lens.

In Galileo's time, there were only low strength lenses available. Due to this restriction, Galileo decided to make his own lenses. He was soon able to achieve a magnification of 9x with lenses hat he had ground himself. His telescope was fitted with his own lenses. It was just another feather in his already well-decorated cap.

As time passed, Galileo improvised on his primitive telescope, making several modifications to it. He also demonstrated his invention at the Senate of Venice, and several senators climbed the highest towers of the time to observe the horizon with Galileo's invention. They viewed the distant ships from their perches and decided that the telescope was a very useful military device.

The telescope changed the face of Astronomy and became an indispensable part of the study. Several inventors used the same principle and made telescopes of their own. Gradually over the years, the study of astronomy benefited immensely from the telescope and its uses. The same principle was employed in the construction of much more powerful telescopes that made it possible to understand our plane and its surroundings more comprehensively, all thanks to Galileo's wonderful invention.

How to Use a Telescope – Galileo’s First Telescope and Its History is a post from: Meade Telescopes