Observation of the sky

The Astronomie owes its existence with people who have throughout the Histoire, by passion and curiosity, survey the eyes with the Ciel.
A first approach of this discipline, approached by the practical side while carrying a glance towards this vault of heaven, will reveal the magnificence of its objects. This discovery starts with a simple observation with the naked eye which will reveal the bases of this science as well as a better comprehension of the space which surrounds us and can be prolonged, for the most impassioned, by the use of very powerful astronomical instruments sometimes which will make it possible to study space profond.
For beginning well, it is preferable to know what one can observe according to the instrument one has and advised being if a purchase is considered, the precautions to be taken before looking at certain phenomena and knowing the optimal conditions for the night observation.

Observation with the naked eye (or with Juste a protection)

Diurnal observation

The strong luminosity of the Sun saturates the sky and prevents the observation of the stars of weaker luminosity except for the the Moon, and in favorable conditions, Venus and possibly Sirius, the main difficulty being locating these stars on the bottom of the very luminous sky. The observation of the sky the day can nevertheless reveal some surprises.

The eclipse S

Sun

the sunspots

They are more delicate to observe because require a good vision and must have an important size in order to be visible with the naked eye. They are the base of the solar protuberances on the surface of star and are the sign of the activity of the star which varies recurringly over several years. It is in general only with most extremely of this one than it is possible to observe them without instrument and are appeared as dark spots on the disc. A one day observation on the other makes it possible to note their displacement (and sometimes their evolution) due to the clean rotation of the Sun and that of the Earth around this one.

Conseils for the observation of the Sun

Of the precautions must imperatively be taken to avoid any burn with the eyes and the sunglasses, even darkest, are to be proscribed. The use of a filter is thus essential, energy of the simple glasses of welder (disadvised because not adapted to this use) to that specific for the observation of the Sun, available in the opticians and strongly recommended because getting a good protection of the eyes. In this last category one finds glasses flexible containing sheets of Mylar and the models out of glass, to prefer because better optical quality and less prone to the stripes. For the sunspots, in addition to the filters, one can also see them under certain climatic conditions, the days of Brouillard, when the solar disk is hardly visible through the Nuage S and not too luminous.

Atmospheric phenomena

Phénomènes related to the Sun

Of other interesting observations in relation to the Sun can be made, not directly astronomical because implementing particular atmospheric conditions and not requiring protections for the eyes.

* the Rainbow

Visible at the time of downpours with a clear sky partially in the direction of the Sun, it is an arc of circle of light broken up on all the extent of the visible spectrum “posed” on the horizon in the direction opposed to the Sun and caused by the refraction of the solar rays through the drops of rain. To note that under good conditions, a second less luminous arc, more spread out with the reversed colors, can be observed above the first, space between the two being slightly darker than the remainder of the sky, it is the dark Bande of Alexandre. Under exceptional conditions, a third arc with the colors reversed compared to second is visible in the vicinity of this one. Except exceptional case, these two supplementary arcs are not complete, but are visible only by places, generally with a rather dark bottom of sky. Under conditions even more exceptional, a fourth even a fifth arc are visible, but in the direction (and not on the other hand) of the Sun, which makes their observation particularly delicate.

* the solar halation

Phénomène which can be considering mainly in winter and altitude, it is appeared as a large luminous circle, not very wide in its width and centered on the Sun. It is formed by the refraction of the solar rays through a fine and uniform layer of clouds of high-altitude, the Cirrostratus.

* the parhelions

Provoqués in the same way that the halation but by other clouds and more frequent, they are two luminous spots with the colors often broken up as in the rainbow and located on both sides Sun at a similar distance at the edge of the circle of the halation and being able to join this one.

Night observation

If you have a good sight, do not hesitate to launch you to the conquest of the sky. Indeed, it is possible to distinguish on the celestial sphere, by one night limpid and without the moon, approximately 3 000 star S. Surtout not of light, only one red tinted lamp. Because if not, it is again necessary to wait a moment before seeing all stars. To make an unforgettable observation, it is necessary that you are at least to 100 km of a big city and the mountain, because the air is purer there, to observe the Milky Way. Times, it will be so impressive that you will be afraid of it (for the sensitive to the cold ones). To scan the craters of the moon, to the binoculars are largely enough. To look at more closely, there are not 36 solutions! With a telescope or a telescope. If you do not have any, not panic! Would be you go to the observatory of the corner, or you extend on a long chair while trying to locate stars and the constellations.

The the Moon

Star king of the night, his observation with the naked eye allows already an approach of our only Natural satellite and to better include/understand the changes which affect it.

the phases

They are explained by the position of the Moon, the Earth and the Sun in space.

Its glare coming from the only reflection of the solar rays on its surface, the Moon will present the aspect of a fine crescent visible with the Crépuscule or the paddle when it is located between the Earth and the Sun, a visible half-disc lasting half of the night when it is with the same distance from the Sun as our planet and finally a complete disc present all the night when it is contrary to our star compared to the Earth. The spectacle of a fine crescent of the moon on a dark blue sky, between dog and wolf, is worth the sorrow to be delayed with its contemplation.

a set of trajectories of luminous rays holds also the attention: in his first rising phase or his last downward phase, when it is only one increasing, one can notice that its dark side, to the shade, presents a weak gleam on all its surface making it possible to distinguish the form from the complete disc (visible on the image low). This is due to the solar rays, considered first once by the Earth towards the satellite, then one second time by this one towards us. This long way makes that a small quantity of light reaches us, but sufficient to distinguish it.

the seas

They are the dark spots on the surface of the star, traces of gigantic impacts of Météorite S which took place there is billion years. They represent the basaltic bottom immense crater S. Of composition different and darker than the remainder of surface, this rock, from its extent, gives the impression since the Earth to see seas on the surface of the satellite, which gave their name to these spots. Charts of the Moon available in the trade make it possible to name them.

the eclipse S

According to the same principle as the solar eclipses, the lunar eclipses take place however only night when the Moon is full and that the Earth is placed between this one and Sun. The diameter of the shade of our planet being much larger than that of our satellite, those more frequently take place and have the same aspect whatever the position of the observer on the Earth. At the time of the total phase, the Moon remains visible and has an orange color which is due to the solar rays deviated and tinted by the terrestrial atmosphere.

the lunar halation

Caused by the same weather phenomenon as for the solar halation, this one is presented however under the aspect of a luminous disc to the brighter diffuse edge and of a diameter more reduced than its diurnal equivalent.

The Planet S

With the wire of the nights, an observer will notice stars to move more quickly than the others. Actually they are planets. To distinguish a planet from a star, it should be known that the stars scintillate and the planets little, because of the distance much more important which separates us from the first. Once you found a planet, it is not uninteresting of knowing of which it acts and this is, even with the naked eye, easily realizable. Indeed, all the visible planets have characteristics well with them:

Mercure is almost never visible since it is always located very close to the Sun.

Venus , also called “the white aspect, evening star”, is the most brilliant planet of all and is visible with the Crépuscule or with the paddle because, like Mercure, it is about an interior planet (of which the orbit lies between the Sun and the Earth) and follows the Sun in its race (its maximum elongation is of 28°). To note that its glare (its luminous level, that one calls magnitude) varies according to its phases (as for the Moon) as well as its distance compared to the Earth.
Mars is not exceptionally brilliant but is recognized by its reddish glare. An assiduous observer (over one period of several weeks) will notice easily that this one sometimes made half-turn (it retrogresses): this is explained by the Mars and earthmoving and is a phenomenon which, for this body, takes place roughly every two years and hard in its totality approximately two months. It affects all external planets.
Jupiter , of a yellowish glare, although being able to be confused with Venus, can recognize itself instantaneously: indeed if one observes the equivalent of Venus in the middle of the night, it is Jupiter.
Saturn is much less brilliant than Jupiter.

In addition to planets, there are many other celestial curiosities:

The Milky Way

You install one night in a place moved back far from the big cities so that your eyes are accustomed to the darkness and wait, lengthened, observing the vault of heaven. It is one of the largest spectacles of the firmament than to scan the star myriads which constitute it. In summer you will see a gigantic milky and irregular bar crossing the vault, aspect which was worth its name to him since the Greek antiquity: the Milky Way. It consists of a denser star regrouping compared to the remainder of the sky and represents the section of our Galaxie seen from the interior.

The Constellation S

They are not celestial objects strictly speaking since they constitute an arbitrary star regrouping to form a figure, in general animal or mythological, and this since Greek antiquity for the northern hemisphere. Charts available in the trade give, according to the day of the year and the hour of observation, an outline complete and directed visible constellations at this time. Initiation with the Astronomie also passes by this stage and makes it possible thereafter to be directed easily in the middle of all these stars and to quickly locate celestial North (the pole star), the Galaxie of Andromède or the most luminous star of the sky (Sirius of the Large Dog) for example.

Other celestial objects

the shooting stars

By prolonging your observation you will notice luminous points followed by a trail crossing the sky quickly: the shooting stars . In fact Météorite S often do not weigh more than one gram but which ignites while warming up by friction during their penetration in the denser Terrestrial atmosphere. One can see several tens in one night of them. Certain nights are particularly favorable to their observation because the Earth, in its orbit, regularly crosses clouds of well-known meteorites of the astronomers (see the article shooting star for the dates).

Other phenomena are accessible to the naked eye, like the Comet S, interesting and sometimes splendid like the Halley's Comet in 1910. There are also various objects (Galaxie S, open Amas S and Nébuleuse S) visible but with this level, only under the aspect of milky spots except for the Pléiades in the constellation of the Taureau where various stars are distinguished.

The Councils for the night observation

Except for the observation of the Moon which puts up with practically any condition, the first council is to place itself in a place distant from any important source of light to observe all these phenomena: to avoid the city where the standard lamps are very penalizing and whose pollution creates an opaque veil on which the lights reflect. To appreciate the night more, to move away from the great agglomerations in order to obtain the darkest possible sky. For the same reason, to avoid the nights of the moon, especially when it is practically full because its intense clearness is strongly prejudicial the observation. The eye requiring a time of adaptation the dark (approximately 15 to 30 minutes) to develop its full capacities under these conditions, an intense luminous ray (headlight of car, flashlight,…) “destroyed” this habituation and strongly reduces its capacities, even the source once extinct and this, again during about fifteen minutes. For this purpose, to place an opaque adhesive tape preferably red on the flashlight which will not give whereas the quantity of light strictly necessary to make it possible to read a sky chart for example.
To observe the sky requires space and for this reason it is recommended to choose a released place giving the broadest possible field of view. A place with these characteristics in mountain is thus practically what there is best because also having the advantage of having an air more pur.
Lastly, for comfort, the nights in shift being able to be wet, therefore fresh, of the hot clothes are welcome as well as foldable chairs of camp-site guaranteeing a good position prolonged without tiredness.

Observation with the binoculars

The Jumelles are very useful when one wishes to observe sufficiently luminous but very wide objects. Their weak enlargement indeed makes it possible to scan a broad field of the sky while collecting more light than with the naked eye. They provide images more luminous in addition than a small telescope of 50 Misters.

Thanks to them it is possible to distinguish the form of the lunar crater S. But especially, and in spite of the distance which separates us from the Moon, one can observe the relief of these craters along the Terminateur, the boundary line between the enlightened part and the obscure part of the Moon. The impression of relief is restored by the plays of shade and light in this zone of the Moon where the sunlight is shaving. This spectacle, by its accessibility, constitutes a good introduction to the observation of the stars.

The binoculars find all their interest in the observation of the wide Nébuleuse S and diffuse object like the Nébuleuse S, and occasionally the passages of Comet S. the reason is even due to their nature: the binoculars enlarge the images little and gain in Luminosité. A wide object appears then as a whole (what can not be the case with glasses or a telescope) and with a clearness and contrasts much higher than with the naked eye. The Nébuleuse of Orion is undoubtedly one of most luminous and one of easiest to locate. It is located in the constellation of Orion, a visible in winter, rather large constellation and very easily identifiable with its shape in rectangle and three stars forming the cross-belt of Orion. One can also observe the cluster of the Pléiades, an open stellar cluster composed of about fifteen stars and that one finds by prolonging the belt of Orion, Pleiads being near this axis.

Also in winter (or the summer, late in the night) another spectacle seizing by its wide, and the voyage which it offers beyond the Milky Way, is the observation of the Galaxie of Andromède. Most difficult here is the location which requires to know to identify the principal constellations (see Repérage of the constellations). It will be retained simply that the constellation of Andromède is located under Cassiopée compared to pole star. By fixing the star beta of Andromède to the binoculars, one goes back very slightly towards Cassopiée and one falls on a first small star, then one still goes up very slightly and one sees a star with badly defined contours, it is the heart of the galaxy of Andromède. If the conditions of observations are good, you see appearing a very diffuse oval who are the arms of the galaxy. The star that you see then is site to 2,5 million Année-lumière! It is the most remote star which one can observe with binoculars.

With experiment, provided that the binoculars are well stabilized and with ideal atmospheric conditions, the observers equipped with a very good vision will be able to distinguish the four satellite galiléens of Jupiter, even with simple 8 X 35.

Choice of the binoculars

Their characteristics are determined by two numbers: the first indicates the enlargement, the second the diameter of the opening to the front one. If a report/ratio of high enlargement has a secondary importance, a large opening on the other hand is recommended because they will collect more light and will reveal of as much better the weak objects. Thus, rather than to take 8x35, it is more judicious to choose 7x50.

Conseils during the observation

The recommendations referred to above for the night observation remainder valid, are added those to it specific to this instrument. It is highly recommended to fix them on a tripod (of photographic type for example) in order to stabilize them, make the observation comfortable and not to lose a field the object which will have sometimes had a long time to be sought. Certain models of binoculars are even equipped with a fixing, but of the adhesive tape makes the deal perfectly. To regulate the binoculars in order to obtain the possible Image clearest (if you carry glasses withdraw them, your defect will be generally corrected during the adjustment).
important Recommendation: never not to try to observe the Sun with binoculars. Indeed, no specific filter is planned for this instrument and its direct observation, with the powers of concentration of the luminous rays, would burn the eye irremediably. A similar example is the experiment of the magnifying glass on a sheet of paper or a piece of wood.

Observation with the telescope

A Telescope is an instrument whose objective consists of one or more lenses and who focuses the luminous rays towards a point called hearth. The role of the Oculaire located after the hearth is to form the image so that it is visible for the eye like enlarging this one. A good telescope is an instrument which one keeps all his life, even after the acquisition of a larger telescope.

The glasses, from its reduced opening (thus not very luminous), are particularly adapted to the observation of the Moon and planets. A model 60 mms in diameter makes it possible to observe many details on those. Although the clearness of small glasses is lower than that of good binoculars, it makes it possible to reach the Limite of resolution objective with a sufficient enlargement and thus to observe the details with a better visual comfort.

Jupiter is a star whose study is impossible to circumvent for the beginner equipped with glasses. Its observation clearly lets see the four principal companions of planet who are the satellite galiléens like some details on the surface of planet. It shows how much the astronomical observation is a school of patience. The people who expect large spectacle will have, not to be disappointed, to turn to a more powerful telescope but of which the use requires to control the bases of astronomy. Those which do not wait anything else until to satisfy a curiosity without end will be filled by this universe of which the finest details led to the greatest discoveries. It is with glasses much less powerful than all those sold nowadays in the trade than Galileo discovered the Jupiter moons and than it acquired the conviction of it that Copernic was right: the Earth turns!

With a telescope, it is also possible to follow the phases of Venus and the evolution of its apparent diameter to the wire of the months. Mars appears like an orange disc, but often without the least detail. One can however there too follow the variation of his apparent diameter throughout the year. In a good configuration between Mars and the Earth, when the red planet is with nearest, it is possible to distinguish its polar icecap.

The most remote planet that one can study with the glasses is Saturn. If the conditions of observation are good, it reveals the very beautiful spectacle of its rings. One can follow the evolution of their aspect. In 2002, they were seen of face and will be of profile in 2010. They will be then completely invisible and it will be necessary to await two or three years before re-examining them through glasses. Meanwhile, their aspect changes year by year. With experiment it is possible also to distinguish the satellite Titan.

The glasses are an instrument perfectly appropriate to the study of the Sun, but of the drastic precautions must be taken to avoid any burn of the Rétine. When these precautions were taken, the Sun clearly reveals its tasks which one can see evolving/moving day after day and to move because of its rotation. It is also possible to observe more distinctly than with unquestionable binoculars Nébuleuse S (M42) or globular Amas S (M13). Lastly, let us not forget the Moon, on which a multitude of details are offered to you: craters, mountains, etc As with binoculars, it is the observation on the level of the terminating one which reveals the most details, in particular the reliefs of the Moon.

Choice of the glasses

The disadvantage of the glasses is the problem of the chromatic aberration: when one observes a planet for example, a side of the disc will be red whereas the other is blue. This problem very handicapping can be completely solved with an objective made up of three lenses (a triplet), but the system is expensive. The glasses of this type are much less cumbersome because the length of the tube, for the same focal distance, is reduced. It is in addition difficult to build glasses of more than 150 mm of opening. Still let us add that glasses are very expensive compared to a telescope: one finds glasses 60 mms in diameter at a reasonable price, but starting from 110 mm their value reaches triple of that of their equivalent with miroir.
On the other hand glasses can be easily transported because it is not put out of order easily (the objective is stable), which is an unquestionable advantage. In addition, in glasses, the objective is not partly blocked by the secondary Miroir which one finds in the telescopes, which improves quality of the image, all the surface of the objective being used to collect the light. The best choice (but also most expensive) is the apochromatic glasses which correct all the aberrations (chromatics and spherical).

The Councils of use

Sun: Its observation, even more than with binoculars (see higher), must be accompanied by the most strict security measures. The burn of the retina is painless, but it is irreversible ! It is thus necessary to use filters of which exists two types: filter SUN, assembling itself to the back on the eyepiece, often sold with the glasses. Its use alone is not adapted because it is subjected to strong temperatures which quickly make it burst. Its use must be combined with a Hélioscope of Herschel which disperses heat. This accessory is generally on sale only in the specialized shops. The second model, it, are placed at front, on the objective, and reduce luminous flow before its entry in the instrument. More expensive, it is the surest solution, on the condition of using the adequate filter. This solution has in its favor a double advantage: laid out out of the optical system, therefore with room temperature, there is no risk which it breaks because of heat. In addition, placed in front of the glasses, before the image is not formed, its defects will influence less the quality of this one than the first type of filter installed on the eyepiece right before the eye.

In all the cases , to carefully check the assembly before beginning the observation from the Sun. It is never ridiculous to place a few moments a sheet of paper behind the eyepiece in order to confirm that all is in order and that the luminosity is not too strong: your sight does not have a price. Lastly, do not forget to stop before small sight tube.

the Moon: Its phase full , which can appear spectacular, presents in fact little interest. Indeed, having since the Earth a line of vision parallel with the solar rays, one does not distinguish any more shades on his surface which make it possible to see the details of them. Thus, to prefer the periods before or after this stage and to concentrate the observation on the zone in extreme cases of the enlightened part and that in the shade, where the rays shave its surface and read out best accident of the ground.

It should be noted that there exist also filters which one places on the eyepiece at the time of the observation of the Moon in order not to be dazzled by the very strong clearness of the star at the time of its full phase . Contrary to the Sun, there is not in this case of danger in the event of lapse of memory of the filter. Its use is however recommended because it filters UV reflected by the surface of the Moon. Filters MOON should not be used for the observation of the Sun.

L' observation with a télescope

A telescope does not consist of lenses but of Miroir S. The latter being cheaper to manufacture, one can, for the price of glasses, to acquire an instrument with the large diameter which gives access to major space. Nevertheless, to benefit from the power of a telescope, it is necessary to have a good site of observation to the shelter of the lights of the city, without what the use of good glasses is preferable.

With a telescope of 150 mm opening the observer will be delighted to be able to distinguish the spiral arms from some Galaxie S and the details in many stellar Amas S or nebulas. With such an instrument, the majority of the objects of the Catalog of Messier can be appreciated with many details. These instruments are also very interesting when they are used for the observation of the planets of which they reveal, thanks to their best To be able of resolution, a multitude of details like the Grande red Jupiter, visible spot with a telescope of 200 mm or the Division of Cassini in the Saturn's rings. It becomes possible to follow the changes of aspect of principal planets of the Solar system to the wire of the months, and the craters of the Moon appear with all their details on the terminating one.

A sufficiently powerful telescope (300 mm) opens the way with hunting for the Comet S, the graal of the astronomers amateurs. All dream to be the first to discover a new star to which, in addition, they will give their name. The comet hunters constitute a world a little with share in the Astronomie amateur. In addition to an expensive material, the search for comet requires a great rigor, it is tiresome because it requires to carry out systematic observations, but certain amateurs count nearly ten of these stars on their table hunting.

Whatever the type of observation carried out, it is while launching out in the Astrophotographie that one benefits the best from his instrument. By lengthening the exposure time, the luminosity and contrasts of the image allow to reveal the finest details. The best solution, henceforth with the range of everyone, is the use of a Capteur CCC connected to a Ordinateur. One finds these sensors in all the electronic devices having capacities of catch of sight (Webcam, numerical cameras, cellphones, etc). The sensors present in these apparatuses can be used in astrophotography CCC, but the best images are obtained with monochromatic sensors. In all the cases, a little do-it-yourself is necessary. In all the cases, the amateur of astronomy which wants to become astronomer amateur must be initiated with the basic principles of optics to be able to carry out its own do-it-yourself because the instruments of series on sale in the trade never have optimal performances.

Types of telescopes

There exist two principal types of telescopes: the Newton and the Schmidt-Cassegrain .

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