Jumat, 27 Mei 2016


Using the sextant to measure the altitude of the Sun above the horizon

A sextant is a doubly reflecting navigation instrument used to measure the angle between any two visible objects. The principle of the instrument was first implemented around 1730 by John Hadley (1682–1744) and Thomas Godfrey (1704–1749) but it was also found later in the unpublished writings of Isaac Newton (1643–1727). The history of these and related instruments, and their forerunners, may be found in the article on reflecting instruments.

The primary use of a sextant is to determine the angle between an astronomical object and the horizon for the purposes of celestial navigation. The determination of this angle, the altitude, is known as sighting (or shooting) the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. Common uses of the sextant include sighting the sun at solar noon or Polaris at night (in the Northern Hemisphere) to determine latitude. Sighting the height of a landmark can give a measure of distance off and, held horizontally, a sextant can measure angles between objects for a position on a chart.[1] A sextant can also be used to measure the lunar distance between the moon and another celestial object (such as a star or planet) in order to determine Greenwich Mean Time and hence longitude.

Why Einstein never received a Nobel Prize for relativity?

The Nobel Committee at that time know actually error in the famous eclipse experiment of 1919, althought F.W.Dyson writes in 'A Determination of the Deflection of Light by the Sun's Gravitational Field, from Observations made at the Total Eclipse of May 29, 1919': "It seems clear that the effect found must be attributed to the Sun's gravitational field and not, for example, to the refraction by coronal matter"
F.W. Dyson's statement is incorrect, because it is clear from Einstein's proving method - that photographs be taken of the stars immediately bordering the darkened face of the sun during an eclipse and compared with photographs of those same stars made at another time - this means that Einstein ignored the refraction of light, and ignored the celestial sphere coordinates system.
" The Nobel citation reads that Einstein is honoured for 'services to theoretical physics, and especially for his discovery of the law of the photoelectric effect'. At first glance, the reference to theoretical physics could have been a back door through which the committee acknowledged relativity. However, there was a caveat stating that the award was presented "without taking into account the value that will be accorded your relativity and gravitation theories after these are confirmed in the future".
Why didnt Albert Einstein win a Nobel Prize for his work on Special General Relativity-Quora

Fundamental  Concepts

     The observation on the stars in the sky at night give an idea, that all the stars are located at a surface of the space perfectly round circle. In astronomy, perfectly round circle is called the Celestial Sphere. And we as observers are in the center of the celestial sphere. The celestial sphere is an imaginary of a dome or a hemispherical screen. The celestial sphere is a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant.
    If we want to determine position of a point on the celestial sphere, it was first envisaged the existence of a horizontal front through the eye of the observer. The front imagination through the eyes of an observer is a special front on the earth, because of this imaginary front parallel to the surface sphere of arbitrarily large radius, concentric with earth. All objects in the observer's sky can be thought of as projected upon the inside surface of the celestial sphere, as if it were the underside of the sea. In astronomy, this front  is called Horizon. 

The Horizontal Coordinate System

Azimuth is measured from the north point (sometimes from the south point) of the horizon around to the east; altitude is the angle above the horizon.

Altitude and Azimuth of Star

- Altitude : is the angle between the line of the horizon and direction of the star seeing by an observer. Alternatively, some arc of the circle straight through the center of celestial bodies, is calculated from the front of the horizon to the star.

- Distance of culmination of a star, is the angle between the  line direction of a star with the normal line of an observer. Alternatively, some arc of the circle straight through the center of celestial body, calculated from Zenith to the Star.

- Azimuth : is the angle between the celestial meridian with the star meridian . Alternatively, some arc of the horizon (the earth's equator), calculated from points north or south to the point of the circle sit up straight through the center of the celestial body.

    Azimuth and Altitude  of stars change at any time due to the daily movements of the stars. Therefore, writing azimuth and altitude  of the stars must be included local time (to mention hours, minutes, and seconds), and the location of an observer (mention latitude and longitude), as well as the height of an observer calculated from the surface of the sea.

     Aside from Horizontal System in Celestial Coordinate Systems we know Equatorial system, Ecliptic system, and Galactic system.

The equatorial coordinate system


The equatorial coordinate system is basically the projection of the latitude and longitude coordinate system  on Earth, onto the celestial sphere.

We can think of coordinates on the sky in terms of angles, time.(in space):  or Astronomical Coordinates./The Celestial Sphere Coordinates, in 3 Dimensional or more precisely 3D+1D Space And Time.

About 3D+1D

Time is the sequence of events, and a separate "dimension".  4 D spacetime was misunderstanding. It is not 4D but 3D + 1D.: The Space and Time. In modern astronomy The Space and Time is The Celestial Sphere Coordinates System.

Actually, time is not dimension, but considered as a dimension just for models in mathematics. In reality there are only three dimensional of space. There are no other dimension.  If we write the celestial spheres in the formula: 3D+1D (The Space and Time), it means the universe as a three-dimensional space in connection with the daily movement of celestial bodies in the passage of time.


The ecliptic coordinate system

In the ecliptic system of coordinates, the fundamental great circle is the ecliptic.The zero-point is still the vernal equinox. Take K as the northern pole of the ecliptic, K' as the southern one. To fix the ecliptic coordinates of an object X on the celestial sphere, draw the great circle from K to K' through X.

The ecliptic (or celestial) latitude of X (symbol β) is the angular distance from the ecliptic to X, measured from -90° at K' to +90° at K. Any point on the ecliptic has ecliptic latitude 0°. (Positional Astronomy).

The Observer's Celestial Sphere

In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with Earth. All objects in the observer's sky can be thought of as projected upon the inside surface of the celestial sphere, as if it were the underside of a dome or a hemispherical screen. The celestial sphere is a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant. 

An observer's celestial sphere depend on geographic position (GP) of an observer (latitude and longitude), for examples, the celestial sphere for an observer in Seatle: 


The celestial sphere for an observer in Oxford, UK, and for an observer in Principe Island, West Africa:

The celestial sphere is only applicable at a certain time and at a certain place on which such observation is performed. In scientific exposure of astronomy, the instant observation applies. It means, all calculations to determine the ‘true position’ and the ‘apparent position’ of a certain star at the sky is only applicable at a certain time and at a certain place on which such observation is performed.

The observation on a star conducted twice from the places with different geographical positions will result the different altitude and azimuth of the star. The altitude and azimuth of a star indicates the position of the star at the time when the observation is performed. The altitude and azimuth of a star changes every time due to the daily movement of the said space objects. Moreover, the observation / photos taking for the stars were performed twice with sufficiently long different interval of time.

You can not calculate the angle of deviation of a star in the sky from two or three places of observations,  to the same of a star, and then to compared it. If this is done, it is not scientific.  Without doubt,  the results will be error.

At a given time, any celestial body is located directly over one point on the Earth's surface. Most navigators will use sextant with sights of three to five stars, if they're available, in 2 -3 minute / not more than 5 minute, to determine their ship's position at sea.


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