INSTRUMENTS

ASTRAL TELESCOPE

BASIC NOTES

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ASTRONOMY COORDINATES
The search for a celestial body by means of its constellation only is not sufficient. In order to identify the celestial body the celestial coordinates, which can be compared to out geographical coordinates, are necessary.
Hypothesizing that we are at the centre of the Earth, and that the Earth is a transparent sphere, around us would be seen the circle we know as the horizon. The horizon cuts the universe into two hemispheres. From our position, stars would be visible that are invisible from other places. It is indispensable to define the place of observation with two coordinates: latitude and longitude. Trace a line that crosses Earth from the North Pole to the South Pole, and imagine a plane perpendicular to that passing through the centre of the planet. This plane intersects the Earth's surface and corresponds to circle known as the Equator. All the points of the Equator have a latitude of 0 °. The North Pole has a latitude of +90 ° and the South Pole has one of-90 °. The minimum distance of any place from the Equator (latitude) can be measured along the arc of a circle that, leaving the nearest Pole passes the place in question, intersects the equator perpendicularly and returns to the opposite Pole. This arc is known as the Meridian. Among all meridians, one has been chosen as a point of reference, that which passes through Greenwich.
Longitude is defined as the angle, measured from the centre of the Earth, found between

Greenwich and the place of observation. It is measured from 0 ° to 180 ° eastwards (positive) or westward (negative). This network or grid, made up of the Equator and the meridians can be transferred to the celestial sphere imagining that we are observing the universe from the centre of a transparent Earth. The stars, like the Sun, rise and set in an apparent rotation called the diurnal arc (apparent because it is, in reality the Earth that moves). Imagine now the lengthening of the terrestrial axis until it intersects the celestial sphere. The two points of intersection will be the Celestial North Pole (austral hemisphere) fig; 15 and the South Pole. the Right Ascension and Declination are the coordinates of the equatorial system.

The first is analogous to the longitude of Earth and the second to its latitude. This permits us to identify the position of the planets in the sky at any given moment. The declination (15) and the angular distance of a planet from the celestial equator,
(fig. 16) positive if the planet is to the north of this last, negative if it is to the South. Therefore the North Pole will have a declination of +90 ° and the South Pole of -90 °. An object situated exactly on the Celestial. Equator will have a Declination of 0 °. The system of measurement is the degree and its submultiple.
The Right Ascension (a is the angle measured rotary wise, starting from the point (g) or ascending node, until it meets the loop of the great circle of planets and its Poles (fig. 16). Point (g), or ascending node is the point where the Sun in its apparent motion on the ecliptic meets the equator in springtime (the spring equinox). At that time, the sun will have the following coordinates:
a = 0h, 0' 0"
d=0 °
The great circle is the imaginary circle generated by a plane intersecting the celestial sphere and passing through its centre. In particular, the great circle passes by the Celestial Poles and the zenith, it is called meridian. The unit of measurement of the Right Ascension is the hour (h), divided by minutes and seconds, the characteristic of this system is that the declination of any planet remains fixed to the revolving of the celestial sphere (fig. 17).
If the stationing of a telescope with equatorial mounting is perfect, the axis of declination, once pointed at the planet, should not be touched any more.