Telescopes | | Are We Underestimating them?

The sky contains a great diversity of astronomical objects that are invisible to the naked eye, but that with a binocular or small telescope becomes perfectly accessible. Examples are star clusters, which contain hundreds and sometimes thousands of stars. Only with our eyes, we can only identify them as small spots in the night sky. Even so, this is only valid for the largest and closest clusters of our Solar System and when observed on a dark night, with no moon and low light around us. But when we look at the clusters with a binocular, they unfold into countless stars, forming a beautiful view; in many cases this is true even in an urban center, such as Porto Alegre.

Are We Underestimating them_

In addition to star clusters, composed of many stars, there are simpler systems, such as double or multiple stars. With the naked eye we see only one point of light. When pointing a 6 cm aperture telescope at this object, or even a 5 cm binocular, we see that the star unfolds in two or more. Example interesting system so it is Alpha Centauri, a 4 to star brightest in the sky, which is close to the Cruzeiro do Sul constellation and is actually composed of 3 stars, two of which are easily visible with a 7×50 binocular (the first number refers to the amplification and the second to the opening of its objective, in mm).  If you are interested in gadgets and stuff then you must check out 

Telescopes | Are We Underestimating them?

The Alfa do Cruzeiro do Sul star is also double, but requires a telescope of about 12cm so that we can separate the stars from the pair. Saturn’s rings, Jupiter’s 4 largest satellites, the phases of Venus and the surface of Mars are other examples of observations that require the help of a binocular or small telescope and that generally cause great excitement in people. Finally, we cannot fail to mention the Milky Way, which is the strip in the sky where the stars of our Galaxy are concentrated. With the naked eye we see only a “fog” crossing the sky, we still need to get away from the artificial lights to see this. But that “fog” unfolds in thousands of stars when it is “covered” with a binocular (7×50, 10×50) or a telescope of 6 cm or more!

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But ” not everything is flowers“in amateur Astronomy. There are two basic difficulties to be overcome by those who want to enjoy the pleasure of observing the night sky. The first is knowing which way to look. That is, how to identify the position in the sky of planets, double stars or stars. The answer lies in learning how to use the celestial charts, which are like maps, showing the position of these objects. We have to keep in mind that the sky visible to an observer depends on the time of year, the time of night and its latitude on the Earth’s surface. There are several celestial charts available, but currently there are also computer programs that simulate the sky for a given date, time and place. Examples: Stellarium , Cybersky , StarCalc and Xephem.

In addition to the initial difficulty in recognizing the sky and where its treasures are located, there is also a risk of frustration with the images obtained by the observation. This is because the images obtained from observing the sky through a telescope or binoculars do not have the same quality as images published in magazines or newspapers, or on websites. The published photos are obtained with telescopes up to 10 meters in diameter, costing hundreds of millions of dollars, or by the Hubble space telescope, a 2.5 meter diameter telescope orbiting the Earth, which cost more than 1.5 billion dollars, and since 1993, when its optics were corrected, it has been producing spectacular images from planets in the solar system to the most distant galaxies observed to date. In particular, very faint objects, such as galaxies and nebulae, require telescopes larger than those most commonly accessible to amateurs in order to be detected only. But with that in mind and a dark, cloudless night, using a binocular or spyglass can be a source of great entertainment.

The small telescopes of 6 cm in diameter cost around R $ 400.00 and those with equatorial mounting almost R $ 800.00.

The best telescope for a beginner is a Newtonian with Dobsonian mount, in honor of amateur astronomer John Dobson (1915-), 6 inches (15 cm) in diameter. This telescope, being high-azimuth, is very easy to assemble and use. Unfortunately, there are no major manufacturers in other major countries, and a telescope of this type costs around US $ 400 in the United States. Plans for building a telescope like this can be accessed at

One of the difficulties with telescopes, in general, is their size. A very small telescope (below 6 cm in diameter) has very little use in astronomy, except for looking at the Moon, and a larger telescope has a locomotion problem; an amateur telescope needs to be mobile so that it can be transported to a suitable dark place. Even a 6-inch Dobsonian, mentioned earlier, is 1.2 meters long, and although it is light, it already occupies a large part of a car’s seat.

The Core

A telescope of smaller physical size, but which allows a sufficient magnification to observe Saturn’s rings, can be a Maksutov-Cassegrain or a Schmidt-Cassegrain of 8 to 12 cm in diameter, or a 10 cm apochromatic Newtonian (achromatic) reflector or higher, but all of these cost over $ 1000. The term apochromatic indicates that the lenses are made of special glasses that eliminate colored, artificial fringes around shiny objects, allowing different colors to be focused on the same point. Note that the Newtonians invert the image, and therefore are not suitable for use during the day, for looking at objects on Earth. It is very important to emphasize that the sun should not be seen through any telescope or binoculars, as it causes irreversible damage to the retina of the eye, without any pain! There are special sunscreens, projection of the image of the Sun.

A refracting telescope uses a pair of lenses to produce the image, while a reflecting telescope uses a primary mirror. For small telescopes, an apochromatic refractor produces a sharper image than a reflector of the same size. But the cost of a reflector is lower, and a larger, and therefore more luminous, reflector is usually obtained for the same price as a smaller refractor.

Another important factor in the choice is the resolving power , the smallest angle between two parts of the image for which the parts remain separate and defined. Resolution power = 120 “/ D (mm) , where” means seconds of arc and 1 “= 1/3600 °.

The resolution of the human eye is about 4′.

A key item in any telescope is the tripod, which needs to be tall enough for comfortable viewing, and must be very rigid so as not to vibrate, which would cause the image to move. Note also that the stars move in the sky, due to the rotation of the Earth, in addition to the movement of comets, satellites and planets. The larger the telescope, the smaller the field of view, that is, the smaller the part of the sky that is visible at the same time in the eyepiece, and therefore the shorter the time that a star will remain in the field. For reasonable magnification, the stars leave the field in a few minutes. To compensate for this movement, it is necessary to refocus the object, manually or by motorized movement. If the assembly is high-azimuth, the refocusing will have to be done in two axes, using two different controls. If the assembly is equatorial,

To use the telescope for photography it is necessary that it is motorized, to allow long exposures, and the Dobsonians are not suitable. The cost of a motorized telescope, with mounting rigid enough to prevent vibration, and with adapters for the camera, will be above $ 2500 in the United States.

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Note that in addition to the telescope itself, the system must contain a 6×30 finder telescope, that is, 6 times magnification and 30 mm in diameter, with a Kellner lens [Carl Kellner (1826-1855)] (K), modified achromatic (MA) or Plössl [Georg Simon Plössl (1794-1868)], and assembled with six support points. A Kellner eyepiece combines an achromatic lens with a single lens, and typically has a field of 40 ° to 50 °. A Plössl uses two achromatic lenses, and has a slightly larger field. More recent are the Erfle [Heinrich Valentin Erfle (1884-1923)], with six or seven components, and 60 ° to 70 ° of field, and the Nagler [Albert Nagler (1935-)], with eight or more elements, and field up to 85 °.


Note that all lenses should be coated ( coated ) with films that reduce reflection. A normal lens reflects about 5% of the incident light per surface, so a system containing, say, 5 uncoated lenses loses about 40% of the incident light just by reflection. Silicon dioxide and lithium fluoride are two materials used to coat the lenses, minimizing reflection. If you have any queries regarding telescopes or any other related gadget then let us know in the comment section.


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