How to find celestial objects from Stellarium star charts using a telescope

Hello everyone! Perhaps the readers of the Habr resource will be interesting. This article is intended to provide some explanations for using star cards generated by the application for smartphones and tablets Stellarium. The article also sets out the real experience of finding faint objects of Deep-Sky using a telescope.


Search for deep space objects using the 300mm Dobson telescope (pictured by K. Radchenko)

Probably many readers use an Android application or a PC program: Stellarium. This resource reflects the area of ​​the sky highlighted by the immediate proximity of the constellations, and the characteristic time of the year: a group of winter constellations, autumn constellations, and the like. The program’s functional makes it possible to mark the lines of the constellations on each map, to give designations of all supporting stars and stars, which facilitate the search for support, in Greek or Latin letters or Arabic numbers. The locations of the objects are circled either by a circle whose diameter is 1-1.5 °, or by a rhombus, or a square, etc. pointers, depending on the class of the object. Next to each circle is a designation of the object it defines. Designations of objects are given in the most common catalogs. Designations of objects from the supplemented Messier catalog are ordinary:letter M with the serial number of the object. Designations of objects from the New General Catalog (NGC) of Dreyer are given only by a number greater than 110. In the designations of objects from the Additional Catalog (IC) the letters are stored: IC 2149.


A general map of the starry sky, built by the Stellarium program.

In order not to clutter up the map with unnecessary inscriptions, it is better not to display the names of the constellations: these names are easily set according to the usual star shape, the boundaries of the constellations and the objects included in them. In the grid, there is no need for the same reason. The local distortions of some angular sizes and distances are quite tolerable.

If the night is supposed to be good and there is the opportunity to observe, then for starters it is possible to determine, using a moving map, the type of starry sky at the time of observation. By determining which constellations will be visible at the time of observation, you can also find out which objects belong to some of these constellations.

Further selection of objects for observation depends only on the desire of the observer and on the conditions of visibility. All proposed objects are interesting without exception, each in its own way.

Suppose some object is selected. Having found a part of the sky in the Stellarium program containing the selected object, the reader will see in more detail the region of the sky with stars up to 5.5 stars that he needs to see with the naked eye. magnitude, he will find the reference star, which is necessarily indicated in the description of this object, will remember how to find it in the sky (otherwise he will have to check the map all the time), and he can get an idea of ​​the location of the object itself among the stars visible with a simple eye.

After that, you should “open the search map” for our object, in other words, “zoom in” the observed region of the sky in the program. Pointing the telescope at the reference star with the help of the finder, or else, you should “guide” the telescope from the reference star (a bright star that is easily located at low magnification, from which they begin to search for weak objects) to the object along the “star path”, looking into the finder or the telescope itself at a magnification of 20x — 40x and focusing on stars up to 10 stars. quantities. Of course, a search map will help you with this, but first you need to figure it out.


Stellarium Star Sky Search Map

When you point the telescope at a reference star, then into the finder (which often does not happen), or rather into the telescope itself with the indicated magnification, you will see it in the center of the field of view, surrounded by other stars.

Focus the telescope carefully so that the stars are visible as small, diamond shots on the black velvet of the sky, and the eye looks at them calmly, without any tension. For most weak, extended objects, the slightest violation of sharpness is enough to completely not see them even when they are present in the field of view of your instrument and fundamentally accessible to it.

The stars surrounding the reference must be identified with the stars in the vicinity of the reference on the search map. To do this, you need to know what field of view is visible through the telescope, what is its angular diameter.

The angular size of the visible field of view at a given magnification (20x — 40x) can be calculated by various methods. The easiest way to remember and figure out how many times the diameter of the full moon will fit in the diameter of the field of view. Usually at 20x-40x the diameter of the field of view is 1.5-2 °.

Having mentally outlined a circle of about this size around the reference on the map, you can more easily identify the stars. It should be noted that it may be necessary to rotate the search map in front of you to "combine" the stars in the telescope and in the vicinity of the reference on the map. Your telescope can “see” too faint stars, for example up to 12 stars. values, while on the search map the weakest have a value of 9.75 stars. quantities. The seeker, on the contrary, can hardly show stars only up to 9 stars. quantities. Therefore, it is necessary to pay attention first of all to the brightest ones (both in the telescope and on the map), and only then, when evaluating the magnitude, take into account the faint stars, sifting out the super-weak ones. In addition to everything, it should be remembered that the eye in the telescope sees stars of different gradations in brilliance,while on the search map there are only four such steps, combining several different magnitudes.

It is also worthwhile to warn the reader that among the stars very often there are doubles and multiples; some (not all) of them can easily be resolved at magnifications of 20x — 40x. If you do not pay attention to the stars with rays on the search cards, considering them single, then you can get confused with the identification and not find multiple stars allowed by the telescope. Because of this, you may not even understand the star pattern in the field of view of the telescope. At the same time, a careful study of multiple stars will subsequently give a more confident identification, especially if the telescope allows them. Such stars will become a kind of milestone that will facilitate the search. Sometimes bright multiple stars help to determine which part of the sky the search map shows in an enlarged and detailed form.

With the accumulation of experience, the identification and selection of stars will be carried out automatically.

When the observer has fully studied the vicinity of the reference star, one can begin to “lead” the telescope. To do this, you need to think over and plan in advance according to which stars to carry out "guidance" - select the "star path" on the search map.

Firstly, we know the width of this “path”: it is equal to the diameter of the supporting neighborhood. True, the telescope may stray from the “path”, but this is not so significant. Secondly, it is necessary to establish the relative position of the reference and the object on the map. Perhaps among the stars scattered between them there are groups, sequences that form characteristic figures similar to the figures of constellations; distinguished by brilliance, a special configuration ("chains", "triangles", "heaps" and the like). Then it is not necessary to “pave” a direct “path”, but to go along a winding path. Of course, there are very rich, star-strewn areas of the sky, and it is difficult to distinguish a noticeable “path”. There are also very poor areas in which there are very few stars. For example, object M55 is located on a very empty field, and the reference star is very weak and does not have a stellar neighborhood (!), I.e.in fact, there is only a poor neighborhood of the M55 itself. There is nothing to be done, although with the help of the finder the telescope can be pointed at this uncomfortable reference, far from bright stars. Nevertheless, an object can be detected, since its luster is not too weak, and it can be noticed if it flickers in the field of view.


The Ghost star cluster M55

For object M62, the “path” runs approximately along the border of an extended star-strewn region with relatively “empty” space


The cluster of galaxies “Lion Triplet” M65

For the very rich star search maps, the “path” should be chosen very carefully, though orienting oneself into bright stars, sometimes skipping the faint.

For poor search stars with stars, it may turn out that there are almost no stars in the vicinity of the reference one and you have to divide the “path” itself into “islands” and take the telescope very carefully: from the “island” to the “island”, when one is already out of sight, and the next one does not appear yet. In this case, you will have to "search" a little with a telescope until the next "island" meets.

It takes time to mentally “turn” them into their usual position. A poorly studied neighborhood of a weak object should generally be tried to orient in the field of view in the position in which you studied it for the first time. Usually, when observing, they use a swivel mirror at the refractor, and, turning it together with the eyepiece, it is easy to rotate the field of view. With a reflector, such a turn is easier to carry out.

When the object is very noticeable, then you yourself will see how it “floats” to you in the field of view due to its edge. If the object is very weak or inconspicuous, then it is necessary to place its entire neighborhood in the field of view so that the position of the object indicated in the search map is in the center of the field of view.

I hope this article will be useful to someone, clear sky and successful observations!

Sincerely, Konstantin Radchenko, Group Editor-in-Chief, Open Astronomy VK