The highest point above the observer's head. Zenith

The celestial sphere is an imaginary spherical surface of arbitrary radius, at the center of which the observer is located. Celestial bodies are projected onto celestial sphere.

Due to the small size of the Earth, in comparison with the distances to the stars, observers located in different places on the Earth's surface can be considered to be in center of the celestial sphere. In reality, no material sphere surrounding the Earth exists in nature. Celestial bodies move in the boundless cosmic space at very different distances from the Earth. These distances are unimaginably great, our vision is not able to evaluate them, therefore to a person all celestial bodies seem equally distant.

Over the course of a year, the Sun describes a large circle against the background of the starry sky. The annual path of the Sun across the celestial sphere is called the ecliptic. Moving around ecliptic. The sun crosses the celestial equator twice at the equinoctial points. This happens on March 21 and September 23.

The point on the celestial sphere that remains motionless during the daily movement of the stars is conventionally called the north celestial pole. The opposite point of the celestial sphere is called the south celestial pole. Residents of the northern hemisphere do not see it, because it is located below the horizon. A plumb line passing through the observer intersects the sky above at the zenith point and at the diametrically opposite point, called the nadir.

The axis of apparent rotation of the celestial sphere, connecting both poles of the world and passing through the observer, is called the axis of the world. On the horizon below the north celestial pole lies north point, the point diametrically opposite to it is south point. East and West points lie on the horizon and are 90° from the north and south points.

A plane passing through the center of the sphere perpendicular to the axis of the world forms celestial equator plane, parallel to the plane of the earth's equator. The plane of the celestial meridian passes through the poles of the world, the points of north and south, zenith and nadir.

Celestial coordinates

A coordinate system in which the reference is made from the equatorial plane is called equatorial. The angular distance of the star from the celestial equator is called, which varies from -90° to +90°. Declension considered positive north of the equator and negative south. is measured by the angle between the planes of great circles, one of which passes through the poles of the world and a given luminary, the second - through the poles of the world and the point of the vernal equinox lying on the equator.

Horizontal coordinates

Angular distance is the distance between objects in the sky, measured by the angle formed by the rays coming to the object from the observation point. The angular distance of the star from the horizon is called the height of the star above the horizon. The position of the luminary relative to the sides of the horizon is called azimuth. Counting is carried out from the south clockwise. Azimuth and the height of the star above the horizon is measured with a theodolite. Angular units express not only the distances between celestial objects, but also the sizes of the objects themselves. The angular distance of the celestial pole from the horizon is equal to the geographic latitude of the area.

The height of the luminaries at the climax

The phenomena of the passage of luminaries through the celestial meridian are called culminations. The lower culmination is the passage of luminaries through the northern half of the celestial meridian. The phenomenon of a luminary passing through the southern half of the celestial meridian is called the upper culmination. The moment of the upper culmination of the center of the Sun is called true noon, and the moment of the lower culmination is called true midnight. The time interval between climaxes is half a day.

For non-setting luminaries both culminations are visible above the horizon, for rising and setting ones lower climax occurs below the horizon, below the north point. Every star culminates in a given area is always at the same height above the horizon, because its angular distance from the celestial pole and from the celestial equator does not change. The Sun and Moon change altitude by
which they culminate.

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

What is the Celestial Sphere

Celestial sphere- an abstract concept, an imaginary sphere of 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 level of the observer’s eyes (in other words, everything that you see above your head from horizon to horizon is this very sphere). However, for ease of perception, we can consider the center of the celestial sphere and the center of the Earth; there is no mistake in this. The positions of stars, planets, the Sun and the Moon are plotted on the sphere in the position in which they are visible in the sky at a certain moment in time from a given point of location of the observer.

In other words, although observing the position of the stars on the celestial sphere, we, being in different places on the planet, will constantly see a slightly different picture, knowing the principles of the “working” of the celestial sphere, by looking at the night sky we can easily find our way around using simple technology. 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 where exactly we are now.

People have long come up with a number of tools to make our task easier. If you navigate the “terrestrial” globe simply using latitude and longitude, then a whole series of similar elements—points and lines—are also provided for the “celestial” 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 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 observer’s point. 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 observer’s vertical with the celestial sphere, opposite the zenith.

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

Axis mundi (Earth's axis)- a straight line around which the visible daily rotation of the celestial sphere occurs. 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 celestial poles are the points of intersection of the axis of the world with the celestial sphere. The celestial pole, located in the region of the Ursa Minor constellation, is called North Pole world, and the opposite pole is called South Pole.

A great 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 is located, and southern hemisphere, where the South Pole is located.

Or the observer's meridian 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 earthly meridian and divides the celestial sphere into eastern And western hemisphere.

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

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

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

Vertical of the luminary

Vertical of the luminary, or height circle, - 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.

Declension circle, or , is 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 luminary parallel to the plane of the celestial equator. The apparent daily movement of the luminaries occurs along daily parallels.

Almucantarat luminaries

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

All the above-mentioned elements of the celestial sphere are actively used to solve practical problems of orientation in space and determining the position of luminaries. Depending on the purpose and measurement conditions, two different systems are used spherical celestial coordinates.

In one system, the luminary is oriented relative to the true horizon and is called this system, 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 an inaccurate reading of the Arabic expression سمت الرأس ( Samt ar-ra's), meaning "direction to the head" or "path above the head". In the Middle Ages during the 14th century, this word came to Europe through Latin and, possibly, through Old Spanish. It was shortened to samt("direction") - samt and with spelling errors transformed into senite - senit. Via Old French and Middle English word senite finally turned into a modern word in the 17th century zenith .

Relevance and use

The concept of "zenith" is used in the following scientific contexts:

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

Thus, it is connected with the concepts of the elements of the celestial sphere - a plumb line and a circle of the height of the luminary.

Strictly speaking, the zenith is only approximately associated with the local meridian plane, since the latter is defined in terms of the rotational characteristics of the celestial body, and not in terms of its gravitational field. They coincide only for an ideal symmetrical body of revolution. For the Earth, the rotation axis 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 over time (for example, due to lunar and solar tides and low tides).

Sometimes the term zenith refers to the highest point reached by a celestial body (Sun, Moon, etc.) during its apparent orbital movement relative to a given observation point. However, the Great Astronomical Dictionary gives the following definition of zenith:

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

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

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

zenith - Zenith, plural. no, m. [from Arab. samt – direction; arose by misreading the letter “m” as “ni”]. 1. The highest point of the celestial sphere, located above the observer’s head (astronium). The sun is at its zenith. 2. transfer The highest degree of something. Large dictionary of foreign words

zenith - zenith, -a Spelling dictionary. One N or two?

zenith - ZENIT a, m. zénith, German. Zenit<, лат. zenith. 1. астр., геогр. Солнце прямо в верху нашего зенита или главной точки стоит. Алярд 132. Зениф и надир, называются полы горизонтовы, и отстоят от горизонта в равном разстоянии. Кн. навиг. 2 7. | В сравн. Dictionary of Gallicisms of the Russian language

zenith - Borrowed from French, where zenith is a rearrangement of the Arabic word semt - "road". See anti-aircraft gun. Krylov's etymological dictionary

zenith - noun, number of synonyms: 13 apogee 13 crown 19 top 34 top 213 highest level 8 highest point 9 team 163 culmination 12 society 61 limit 39 height 10 degree 32 point 100 Dictionary of Russian synonyms

zenith - Zenit/. Morphemic-spelling dictionary

zenith - zenith I m. The highest imaginary point of the celestial sphere, located above the observer’s head and opposite to the nadir (in astronomy). II m. The highest degree, the highest limit, the top of something. Explanatory Dictionary by Efremova

zenith - ZENIT metro gr. a mental point in the sky, vertically above an earthly object or point; parietal point, crown. The continuation of this plumb line will pass through the center of the earth and mark the nadir on the opposite side of the imaginary firmament. Zenith, related to the zenith. Dahl's Explanatory Dictionary

zenith - see >> apogee, highest Abramov's dictionary of synonyms

zenith - -a, m. 1. astr. The highest point of the celestial sphere above the observer's head. The sun is at its zenith. □ The gentle moon is almost at its zenith, and from end to end over the native steppe there is a twinkling scattering of small stars like spring. Sholokhov, Light and Darkness. 2. transfer Small academic dictionary

zenith - The point on the celestial sphere located directly above the observer's head. The astronomical zenith is formally defined as the intersection of a plumb line with the celestial sphere. Large Astronomical Dictionary

zenith - ZENIT, a, m. 1. In astronomy: a point on the celestial sphere located vertically above the observer’s head. 2. transfer The highest degree, the pinnacle of something. (high). At the zenith of glory. | adj. anti-aircraft, aya, oh (to 1 value). Ozhegov's Explanatory Dictionary

Zenith - I Zenith (French zénith, from Arabic zemt, literally - path, direction) a point on the celestial sphere (See Celestial sphere), located above the observer’s head; in the west, the celestial sphere is crossed by a line directed vertically upward from the observation site. Great Soviet Encyclopedia

All celestial bodies are at unusually large and very different distances from us. But to us they seem equally distant and seem to be located on some 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 moment of observation.

The celestial sphere is an imaginary sphere of infinite 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 combined with the center of the Earth. The luminaries are applied to the sphere in the position in which they are visible in the sky at some point in time from a given point of location of the observer.

The celestial sphere has a number of characteristic points, lines and circles. In Fig. 1.1, a circle of arbitrary radius depicts the celestial sphere, in the center of which, designated by point O, the 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 is the point of intersection of the observer's vertical with the celestial sphere, located above the observer's head. Nadir Z" is the point of intersection of the observer's vertical with the celestial sphere, opposite to the zenith.

The true horizon N E S W is a great 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 above-horizon hemisphere, in which the zenith is located, and the subhorizon hemisphere, in which the nadir is located.

The world axis PP" is a straight line around which the visible daily rotation of the celestial sphere occurs.

Rice. 1.1. Basic 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 celestial poles are the points of intersection of the axis of the world with the celestial sphere. The celestial pole located in the region of the Ursa Minor constellation is called the North celestial pole P, and the opposite pole is called the South Pole.

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 Celestial Pole is located, and the southern hemisphere, in which the South Celestial Pole is located.

The celestial meridian, or observer meridian, 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 earthly meridian and divides the celestial sphere into the eastern and western hemispheres.

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

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

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

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

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

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 aviation astronomy.