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The astronomical meridian is also determined by the zenith, and is defined as a circle on the celestial sphere that passes through the zenith, nadir, and the celestial poles. A zenith telescope is a type of telescope designed to point straight up at or near the zenith, and used for precision measurement of star positions, to simplify telescope ...
Diagram showing the relationship between the zenith, the nadir, and different types of horizon.Note that the zenith is opposite the nadir. The nadir [a] [b] is the direction pointing directly below a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface.
Thus, where the zenith is directly above an observer, the nadir is underfoot. The zenith and nadir form the two poles of the horizon line. naked eye. Also bare eye or unaided eye. The human eye as used without any magnifying or light-collecting optical aid, such as a telescope, nor any eye protection.
The history of light therapy can be traced back to ancient Egypt and India, where therapy with natural sunlight was first used to treat leucoderma. [3] In the 1850s, Florence Nightingale's advocacy of exposure to clean air and sunlight for health restoration also contributed to the initial development of light therapy for treatments. [4]
In astronomy, the meridian is the great circle passing through the celestial poles, as well as the zenith and nadir of an observer's location. Consequently, it contains also the north and south points on the horizon , and it is perpendicular to the celestial equator and horizon.
Groombridge transit circle of 1806. The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir.