All celestial bodies are at unusually large and very different distances from us. But to us they appear to be equally distant and as if located on a certain sphere. When solving practical problems in aviation astronomy, it is important to know not the distance to the stars, but their position on the celestial sphere at the time of observation.

The celestial sphere is an imaginary sphere of infinitely large radius, the center of which is the observer. When examining the celestial sphere, its center is aligned with the observer's eye. The dimensions of the Earth are neglected, so the center of the celestial sphere is often aligned with the center of the Earth as well. The luminaries are applied to the sphere in such a position in which they are visible in the sky at some point in time from a given point of the observer's location.

The celestial sphere has a number of characteristic points, lines and circles. In fig. 1.1 a circle of arbitrary radius depicts a celestial sphere, in the center of which, indicated by point O, an observer is located. Let's consider the main elements of the celestial sphere.

The observer's vertical is a straight line passing through the center of the celestial sphere and coinciding with the direction of the plumb line at the observer's point. Zenith Z - the point of intersection of the observer's vertical with the celestial sphere, located above the observer's head. Nadir Z "- the point of intersection of the vertical of the observer with the celestial sphere, opposite the zenith.

The true horizon N E S W is a large circle on the celestial sphere, the plane of which is perpendicular to the vertical of the observer. The true horizon divides the celestial sphere into two parts: the overhorizontal hemisphere, in which the zenith is located, and the subhorizontal hemisphere, in which the nadir is located.

The axis of the world РР "is a straight line around which the visible daily rotation of the celestial sphere takes place.

Rice. 1.1. Major points, lines and circles on the celestial sphere

The axis of the world is parallel to the axis of rotation of the Earth, and for an observer located at one of the poles of the Earth, it coincides with the axis of rotation of the Earth. The apparent daily rotation of the celestial sphere is a reflection of the actual daily rotation of the Earth around its axis.

The poles of the world are the points of intersection of the axis of the world with the celestial sphere. The pole of the world, located in the constellation Ursa Minor, is called the North Pole of the world P, and the opposite pole is called the South R.

The celestial equator is a large circle on the celestial sphere, the plane of which is perpendicular to the axis of the world. The plane of the celestial equator divides the celestial sphere into the northern hemisphere, in which the North Pole of the world is located, and the southern hemisphere, in which the South Pole of the world is located.

The celestial meridian, or the meridian of the observer, is a large circle on the celestial sphere passing through the poles of the world, zenith and nadir. It coincides with the plane of the observer's meridian and divides the celestial sphere into eastern and western hemispheres.

The points of the north and south are the points of intersection of the celestial meridian with the true horizon. The point closest to the North Pole of the world is called the point of the north of the true horizon C, and the point closest to the South Pole of the world is the point in the south of the Y. Points of the east and west are the intersection of the celestial equator with the true horizon.

The midday line is a straight line in the plane of the true horizon that connects points north and south. This line is called midday because at noon local true solar time the shadow from the vertical pole coincides with this line, that is, with the true meridian of a given point.

The southern and northern points of the celestial equator are the intersection points of the celestial meridian with the celestial equator. The point closest to the southern point of the horizon is called the southern point of the celestial equator, and the point closest to the northern point of the horizon is called the north point

The vertical of the luminary, or the circle of height, is a large circle on the celestial sphere passing through the zenith, nadir and luminary. The first vertical is the vertical passing through the points of east and west.

The declination circle, or the hour circle of the luminary, PMR is a large circle on the celestial sphere passing through the poles of the myoa and the luminary.

The diurnal parallel of the star is a small circle on the celestial sphere drawn through the star parallel to the plane of the celestial equator. The apparent diurnal movement of the luminaries occurs along diurnal parallels.

The almucantarat of the luminary AMAG is a small circle on the celestial sphere, drawn through the luminary parallel to the plane of the true horizon.

The considered elements of the celestial sphere are widely used in aeronautical astronomy.

A point of the sky, lying upward, in the direction of the plumb line, at each location on the earth's surface. In astronomy, in addition to this geographical Z., there is also a geocentric ... Encyclopedic Dictionary of Brockhaus and Efron

Points and lines of the celestial sphere - how to find the almucantarat, where the celestial equator passes, which is the celestial meridian.

What is the Heavenly Sphere

Celestial sphere- an abstract concept, an imaginary sphere of an infinitely large radius, the center of which is the observer. In this case, the center of the celestial sphere is, as it were, at the eye level of the observer (in other words, everything that you see above your head from horizon to horizon is this very sphere). However, for simplicity of perception, it can be considered the center of the celestial sphere and the center of the Earth, there is no mistake in this. The positions of the stars, planets, the Sun and the Moon are applied to the sphere in such a position in which they are visible in the sky at a certain point in time from a given point of the observer's location.

In other words, although observing the position of the luminaries on the celestial sphere, we, being in different places of the planet, will constantly see a slightly different picture, knowing the principles of the “work” of the celestial sphere, looking at the night sky we can easily navigate the terrain using a simple technique. Knowing the view overhead at point A, we will compare it with the view of the sky at point B, and by the deviations of familiar landmarks, we will be able to understand exactly where we are now.

People have long come up with a number of tools to facilitate our task. If you are guided by the "earthly" globe simply with the help of latitude and longitude, then a number of similar elements - points and lines are provided for the "heavenly" globe - the celestial sphere.

The celestial sphere and the position of the observer. If the observer moves, then the entire sphere visible to him will also move.

Elements of the celestial sphere

The celestial sphere has a number of characteristic points, lines and circles, let us consider the main elements of the celestial sphere.

Observer vertical

Observer vertical- a straight line passing through the center of the celestial sphere and coinciding with the direction of the plumb line at the point of the observer. Zenith- the point of intersection of the observer's vertical with the celestial sphere, located above the observer's head. Nadir- the point of intersection of the vertical of the observer with the celestial sphere, opposite the zenith.

True horizon- a large circle on the celestial sphere, the plane of which is perpendicular to the vertical of the observer. The true horizon divides the celestial sphere into two parts: overhorizontal hemisphere where the zenith is located, and subhorizontal hemisphere where the nadir is located.

Axis of the world (Earth axis)- a straight line around which there is a visible daily rotation of the celestial sphere. The axis of the world is parallel to the axis of rotation of the Earth, and for an observer located at one of the poles of the Earth, it coincides with the axis of rotation of the Earth. The apparent daily rotation of the celestial sphere is a reflection of the actual daily rotation of the Earth around its axis. The poles of the world are the points of intersection of the axis of the world with the celestial sphere. The pole of the world, located in the constellation Ursa Minor, is called North Pole the world, and the opposite pole is called South Pole.

A large circle on the celestial sphere, the plane of which is perpendicular to the axis of the world. The plane of the celestial equator divides the celestial sphere into northern hemisphere, in which the North Pole of the world is located, and southern hemisphere, in which the South Pole of the world is located.

Or the meridian of the observer - a large circle on the celestial sphere passing through the poles of the world, zenith and nadir. It coincides with the plane of the terrestrial meridian of the observer and divides the celestial sphere into eastern and western hemisphere.

North and South points- points of intersection of the celestial meridian with the true horizon. The point closest to the North Pole of the world is called the point of the north of the true horizon C, and the point closest to the South Pole of the world is the point in the south of the Y. Points of the east and west are the intersection of the celestial equator with the true horizon.

Midday line- a straight line in the plane of the true horizon, connecting the points of the north and south. This line is called midday because at noon local true solar time the shadow from the vertical pole coincides with this line, that is, with the true meridian of a given point.

Points of intersection of the celestial meridian with the celestial equator. The point closest to the southern point of the horizon is called point south of the celestial equator, and the point closest to the northern point of the horizon is point north of the celestial equator.

Vertical luminary

Vertical luminary, or circle of height, - a large circle on the celestial sphere passing through the zenith, nadir and luminary. The first vertical is the vertical passing through the points of east and west.

Declination circle, or, - a large circle on the celestial sphere, passing through the poles of the world and the luminary.

A small circle on the celestial sphere, drawn through the star parallel to the plane of the celestial equator. The apparent diurnal movement of the luminaries occurs along diurnal parallels.

Almucantarat luminaries

Almucantarat luminaries- a small circle on the celestial sphere, drawn through the star parallel to the plane of the true horizon.

All the elements of the celestial sphere noted above are actively used to solve practical problems of orientation in space and to determine the position of luminaries. Two different systems are used depending on the purpose and measurement conditions. spherical celestial coordinates.

In one system, the luminary is oriented relative to the true horizon and this system is called, and in the other - relative to the celestial equator and is called.

In each of these systems, the position of the star on the celestial sphere is determined by two angular quantities, just as the position of points on the surface of the Earth is determined using latitude and longitude.

Origin

Word zenith came from inaccurate reading arabic expressions سمت الرأس ( samt ar-ra's), meaning "direction to the head" or "path over the head." V Middle Ages during the XIV century this word through Latin and possibly through Old Spanish ended up in Europe. It has been shortened to samt("direction") - samt and with misspellings it was transformed into senit - senit... Across old french and middle english word senit finally turned into a modern word in the 17th century zenith .

Relevance and use

Zenith is used in the following scientific contexts:

• It serves as a direction for measurement zenith angle, which is the angular distance between the direction to the object of interest (for example, a star) and the local zenith relative to the point for which the zenith is determined.
• It defines one of the axes horizontal coordinate system in astronomy.

Thus, it is related to the concepts of elements celestial sphere- plumb line and circle of height luminaries.

Strictly speaking, the only zenith approximately associated with the local plane of the meridian, since the latter is defined in terms of the rotational characteristics of a celestial body, and not in terms of its gravitational field. They coincide only for an ideal symmetric body of revolution. For the Earth, the axis of rotation does not have a fixed position (for example, due to the constant movements of ocean water and other water resources), and the local vertical direction, determined through the gravity field, itself changes direction in time (for example, due to lunar and solar ebb and flow).

Sometimes the term zenith refer to the highest point reached by a celestial body (Sun, Moon, etc.) in the process of its apparent movement along orbit regarding this observation point. However, the Big Astronomical Dictionary gives the following definition of the zenith:

The point in the celestial sphere located directly above the observer's head. Astronomical zenith is formally defined as the intersection of the plumb line with the celestial sphere. Geocentric zenith - the intersection with the celestial sphere of the line going from the center of the Earth through the point of the observer's position. The geodesic zenith is on a line normal to the geodesic ellipsoid or spheroid at the observer's position.

Thus, as applied, for example, to the Sun, the zenith can be reached only in low latitudes.