Horizon (redirected from HORIZONS)

horizon, in astronomy, roughly circular line bounding an observer's view of the surface of the earth where the sky and earth seem to meet. This is the visible horizon. At sea the visible horizon is a perfect circle with the observer at its center, but on land it is irregular due to topographic features. The distance to the horizon varies as the square root of the observer's elevation for small elevations; at four times the height the distance to the horizon is twice as great. The celestial horizon, the principal axis in the altazimuth coordinate system, lies halfway between the observer's zenith and nadir. In geology horizon refers to sedimentary deposits of a certain period, usually marked by characteristic fossils.

---

horizon

In pedology, a distinct layer of soil forming part of the vertical sequence in a soil profile. Each horizon differs from the one above or below it in colour, chemical composition, texture, and structure. The horizons become differentiated during soil development because conditions vary with depth. There are generally three major layers within any given soil profile, and they are designated, from surface downward, as A, B, and C horizons. The A horizon generally contains more organic matter than the others; it is also the most weathered and leached. The B horizon tends to be a zone of accumulation, since all or part of the mineral matter removed from the A horizon in solution may be deposited in it. The C horizon consists chiefly of the materials from which the A and B layers were derived; called parent materials, these are only slightly altered, because they are in general not subjected to soil-forming processes.

---

horizon

1. the apparent line that divides the earth and the sky

2. Astronomy

a. the circular intersection with the celestial sphere of the plane tangential to the earth at the position of the observer

b. the great circle on the celestial sphere, the plane of which passes through the centre of the earth and is parallel to the sensible horizon

3. a thin layer of rock within a stratum that has a distinct composition, esp of fossils, by which the stratum may be dated

4. a layer in a soil profile having particular characteristics

---

horizon [hə′rīz·ən]

(astronomy)

The apparent boundary line between the sky and the earth or sea. Also known as apparent horizon.

The distance a light-ray could have traveled since the big-bang explosion at any given epoch in the evolution of the universe.

(geology)

The surface separating two beds.

One of the layers, each of which is a few inches to a foot thick, that make up a soil.

---

horizon

The apparent or visible junction of the earth and sky, as seen from any specific position.

---

Horizon 

the part of the earth’s surface that is visible to the eye of an observer on open terrain. The line along which the sky appears to be contiguous with the earth’s surface is called the visible horizon (see Figure 1). The distance d of the visible horizon, that is, the distance to the most distant visible points of the earth’s surface, depends on the altitude h of the observer’s location above the level of the surrounding terrain and on the relief of the terrain (at sea it depends on the elevation above sea level); it is expressed by the formula d (in (the mean refraction is taken into account in the formula). With an increase in altitude h the distance of the visible horizon increases (see Table 1).

Figure 1. Horizon: ABC is the visible horizon: MM is the plane of the true horizon

The true, or mathematical, horizon is a large circle of the celestial sphere whose plane is perpendicular to a plumb line. The visible horizon usually lies lower than the true horizon, and the angle δ between them is called the lowering of the horizon.

Table 1. The visible horizon in terms of height and distance
h(m)	d(km)	h(m)	d(km)	h(m)	d(km)
1	3.8	9	11.5	80	34.3
2	5.4	10	12.1	90	36.3
3	6.6	20	17.1	100	38.3
4	7.7	30	21.0	200	54.2
5	8.6	40	24.2	300	66.3
6	9.4	50	27.1	400	76.6
7	10.1	60	29.7	500	85.6
8	10.8	70	32.0	600	93.8

The meridian of the place of observation intersects the true horizon at north and south points. Between them on the horizon lie the east point (to the right of the observer who stands facing north) and the west point (to his left). At the east and west points the horizon intersects with the celestial equator. The points north, east, south, and west are called the main points of the horizon.

N. P. ERPYLEV [7–23l–1]

---

Horizon 

in geology, a local stratigraphic subdivision corresponding to a level or sublevel of the generally accepted stratigraphic scale. It includes rocks of the same age with varied lithological composition, sometimes with a definite set of fauna (for example, the Chokrak horizon of the Neocene in the Crimean and Caucasian area). Sometimes the term “horizon” is used to designate a patch of layers of little thickness with distinctive lithological or paleontological features that is well-traced along its course (for example, a horizon with silicic concretions, a coral horizon).

---

Horizon 

a research ship of the Scripps Institution of Oceanography of the University of California (USA).

The Horizon was built in 1944. It is 43.6 m long and 10 m wide, with a 900-ton displacement and a top speed of 25 km per hour. It can cruise autonomously for 48 days, with a range of about 13,000 km. It is equipped with sounding devices, two hydrographic winches, a trawl winch, a bathythermographic winch, and a scientific laboratory. The Horizon was designed for meteorologic and all types of oceanographic observations; it has been used to investigate various regions of the Pacific Ocean. In 1952–53 an expedition on the Horizon discovered the Tonga trough, the greatest depth known to that time (10,633 m).