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The concept of planisphere it is used to describe and identify a letter where the celestial sphere or Earth in a flat . It is a useful instrument for teaching and science. For example: “The teacher asked us to take a planisphere for geography class”, "The grandfather said he will teach me to place the constellations in the planisphere", "The planispheres must be updated from time to time due to scientific discoveries".

As noted when deepening in this regard, it is possible to distinguish between land planisphere and the celestial planisphere . The land planisphere or world map constitutes a cartographic representation based on the surface of our planet land . East Map reproduces on scale the results of a geographical projection of the earth's sphere on a plane.

He land planisphere it can focus on the political division of the world (and then show the boundaries between nations) or on the details physical (exhibiting rivers, mountains and other geographical issues). There are also more specific planispheres, such as geological or topographic ones.

He celestial planisphere , on the other hand, is a star chart that is used to recognize constellations and stars . It consists of a pair of disks that move on a common pivot.

What this planisphere does is show the projection of the celestial sphere on a flat surface, which implies a certain distortion. There are two big methods projection: the polar equidistant azimuthal projection (The sky is drawn centered on one of the celestial poles, with circles of equal decline that appear equidistant from each other and the poles) and the stereographic projection (The distances between the declination circles are enlarged while the constellation format remains unchanged.)

In the disk above it is a representation of the horizon, which graphs the divisible region of the sky for a given moment. In general, the horizon cannot be seen clearly, and this also occurs with the stars. The main reason is that in a basic design, the disk starting from a particular latitudinal point, restricting the celestial portion that will be seen in the planisphere. However, there are models that have different interchangeable parts, as well as others that contain more detail on the same disc.

This characteristic is of vital importance when using a celestial planisphere, since if it is chosen poorly, the study will return inaccurate information. To locate a particular celestial body it is necessary to verify its position at the time of measurement, since they are in constant motion; The planisphere simply offers a Cartesian representation of a point in space, which should be compared with the updated information so that the observation yields correct results.

In certain cases it is possible to adjust the decline (that is the distance measured in angles that exists between a star and celestial Ecuador, which is equivalent to the latitude of the Earth) with a separate piece to the disks, although it shares the same pivot. For the rest of the planispheres, there is the possibility of printing said value on the disk that is in front, parallel to the line that serves as a junction between the poles. On the margin, is the representation of the straight ascension and the chronological data necessary to place on a particular night.

To do this, it is necessary to rotate the disc until the schedule and the day in question, taking into account the change that occurs in the summer. In this way, a representation of the stars that can be visualized at that particular moment is obtained.

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