Simón García
"EAAE Summerschools" Working Group
I.E.S. Aljada. Murcia (Spain)
Abstract
The observation of the sun is one of the activities that one could incorporate to the schools with more easily. It is easy find a moment between the normal hours of class in order to observe and calculate the Wolf's number that measures the solar activity.
These are carried out using the procedure of projecting the image of the sun obtained by means of an any telescopes or prismatic. This is a good way of making it. I propose another form that gives several advantages: the construction and use of a Newtonian telescope, with mirror without aluminising and with open structure, that is to say, without tube.
Many years ago I designed this application extremely simplified of the Newtonian telescope consistent in a wooden structure in form of L and a tripod making with tubes of plumbing. If the mirror is normal, that is, with a reflective layer, we could have a good telescope for the school for a ridiculous price. If we changed the mirror for another without the aluminium layer we have a beautiful helioscope still cheaper. But in this last case the didactic possibilities of the instrument increase very much. One could be built it directly in class and see also how the image is born and the whole optic outline upon having a cone of potent light whose trajectory is perfectly visible from the mirror until the ocular.
Introduction
Human eye as instrument of observation is a little short of possibilities. Really, with a few millimetres more than diameter in the eye, we could differentiate without another optic help Moon's seas and some of their big craters. Also one could appreciate the turn of the moons of Jupiter and the "myriad of stars never seen by human eye" in expression of Galileo, about our Milky Way. A telescope especially designed in order to observe the Sun allow us to observe the Sunspots without danger.
The telescope allows us to see the things much closer or bigger than vision with the naked eye (when they are far). That is what everybody knows. What they no longer know all is that the most important in a telescope, what allow to see things more and more, it is the diameter of their objective, independently of the increases that have combined in their system of lenses. Our telescope, with about 150 or 160 mm. diameter will allow to see objects (stars for example) that they are about ten thousand times less brilliant than the most brilliant stars of the night sky. We will also see details whose angular separation is of seven tenth of second of arch, or what it is the same, we will see the craters that have a superior diameter to the thousand five hundred meters in the Moon. The helioscope participates from all the optic advantages that provides a big diameter for the main mirror in all that it refers to the power separating or of resolution. For that reason we could see the finest details of the sunspots, small pores, the granulation of the photosphere and the contrast of the white flares on the bottom of the photosphere or the dark profile of the chromospheres.
The Sun is the only astronomical object that has too much light in order to observe it. It is dangerous look at it even to mere view. For that reason this instrument is also advisable. A mirror without the reflective layer like which we are going to use alone reflective the 5% of the light that receives. For that reason it is enough a mere filter of which they are used in electric weld, placed before the ocular, so that the observation is comfortable and doesn't offer any danger for the view.
The main disadvantage is the instability of the assembly. It is difficult carry out photographic takings or use oculars of great increase. It supports very good ocular of 25 millimetres of focus from now on. The picture could find a good ally in the modern digital cameras. Nevertheless one could try in order to improve the stability of this assembly completely handmade.
Realization
Placement of the optic parts
Firstly we will assembly with screws and glue the two wood that form the "L" or structure that makes the usage of tube in our telescope (Fig. 1).
In the small part of this L will be placed the "cell" (Fig.2, 3 4) or assembly that supports the main mirror with their three screws, that they will allow to guide the optic axis of the mirror so that point exactly to the diagonal plane mirror or secondary mirror. The three screws fit in easily in other as many holes that has been made in the minor part of the L. Using the springs on the wing nuts they extend or they shrink. They are those that in fact tolerate the weight of the mirror, they for that reason should be quite robust.
The mirror should secure with some small slices in form of angle (Fig.5). This will impede that the mirror falls when it is "face down." The mirror should not be pressed. It has to offer a slight resistance to the turn, but it should rotate when it is caught sidelong, as if it was the cover of a can. It is necessary, to care a lot about the optic surfaces so that they are no dirtied neither they scratched. If the mirror is dirtied of powder, one could remove breathing air. Mirrors shouldn't be neither washed or rubbed. Only in very extreme cases, they will clean the possible stains of fat with a cotton wet in alcohol diluted in distilled water and without rubbing.
The spider
The secondary mirror goes assembled in a support that permits you their orientation in all the senses of the space, with only work some of the screws that takes and that they give you aspect of spider.In order to place the diagonal plane in the long wood of the L (Fig. 1) it will be necessary to keep in mind the focal distance of the mirror. It will be placed in front of the hole of the focuser, that will have been carried out keeping in mind that the focal image of the objective should be formed to about eight centimetre of the external face of the stick of the L. In the case of a mirror of 1,200 mm of focal and 150 mm of diameter, the hole of the focuser will be been supposed to make to one meter of the surface of the mirror objective. And, in general, at about 20 cm less that the focal of the mirror that it is used.
The mount of the telescope
It has also been simplified to the maximum the question about the materials, the weight and the difficulty of construction. It is a little weak assembly, but with a few magnification it works well. Their construction doesn't need of wise explanations. It is enough with looking at the drawing (Fig. 1). The "T" it of plumbing is the Gordian knot that permits the movements in azimuth and height. Through a piece double thread, the "buttress" that are not in the drawings, they are inserted in the wood, fixing it with a nut that are in the drawings in the centre of gravity of the L. With all their assembly elements: mirrors, focuser and eyepiece. Once assembled the group, position will be stabilized in any position, thanks to the resistance that offers the friction of the threads. If in spite of everything there is unbalances, it would be necessary to place any counterbalance tied to the stick of the L.
Alignment of the optic parts
We with all the assembled elements will look through the hole of the focuser without the eyepiece. We aimed to a place very illuminated, that it is not the sun. The most probable thing is that everything is not aligned it be (Fig 6.1).
We will work act first on the screws of the "spider" (Fig. 7 1), until able to see the whole mirror centred inside the field of the focuser (Fig. 6.2). Later we will work on the three wing nuts that move the main mirror and acting meekly we will take the image of the diagonal plane, that will include that of our eye also, to the centre of the mirror (Fig 6.3).
This operation, that is important so that the telescope works well, it is carried out with much ease thanks to the efforts that we have made in order to carry out the spider and the cell, and they permit that our telescope is not like that flute that fell in the noses of the donkey. The flute sounded by chance.
Final test
One we are on ocular will point to the sun (Or a landscape or distant building, if the telescope is for night observation) and we will move the tube of the focuser until it succeeds in focusing. Then we will see the elected object much closer, bigger, with all their details. If a first observation with telescope is safety that it will be an image that won't be forgotten easily. We will also see something that could disappoint us: everything upside down. This should not worry us. In all the big telescopes of the world are so. And the same as they, we will begin to observe the fine details of the lunar surface or of the planets, the nebulas and galaxies or the countless stellar couples that they populate our galaxy. And in the case of the helioscope that occupies us all splendid and changing of solar sunspot, that our star offers especially: The Sun.
References
GARCÍA, Simón.: Construcción de un telescopio newtoniano. Revista Cuadernos de Pedagogía. 1986.
TEXEREAU, Jean.: How to Make a Telescope. Willmann-Bell, Inc. 1984.
EDMUND SCIENTIFIC.: All about telescopes. Barrington. New Jersey. 1970.
THOMPSON, Allyn J. : Making your own Telescope. Sky Publishing Corporation. Cambridge. Massachusetts. 1947, 1973.
KRIEGE,David and BERRY, Richard:. The Dobsonian Telescope. Wilmann-Bell, Inc. 1998.
FERRERI, Walter.: Il libro dei telescope. Il Castello. 1989.
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