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Note that the sign must be included even if positive.
A celestial object that passes over zenith, has a declination equal to the observer's latitude, with northern latitudes yielding positive declinations. A pole star therefore has the declination +90° or -90°. Conversely, celestial objects with a declination higher than , where l is the latitude, are visible the whole sidereal day. Such stars are called circumpolar, while the phenomenon of a sun not setting is called midnight sun.
The declination of all celestial objects vary over time, in different periods.
The declination of the sunThe Sun (also called Sol is the star in our solar system. Planet Earth orbits the Sun. Other bodies that orbit the Sun include other planets, asteroids, meteoroids, comets and dust. Not all objects passing through the solar system have been orbitally capt (Sun Dec) is the angle between the rays of the sun and the plane of the earth equator. Since the angle between the earth axis and the plane of the earth orbit is nearly constant, Sun Dec varies with the seasons and its period is one yearA year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. By extension, this can be applied to any planet: for example, "Martian year". Seasonal year A seasonal year is the time between successive recurrences, that is the time needed by the earth to complete its revolution around the sun.
When the projection of the earth axis on the plane of the earth orbit is on the same line linking the earth and the sun, the angle between the rays of the sun and the plane of the earth equator is maximum and its value is 23°27'. This happens at the solsticesSolstice is an astronomical term regarding the position of the Sun in relation to the celestial equator. It is related to the axial tilt of the planet, and not the Solar apsides ( aphelion and perihelion) of the planet, as many people commonly believe.. Therefore Sun Dec is +23°27' at the northern hemisphere summer solsticeThe summer solstice is an astronomical term regarding the position of the Sun in relation to the celestial equator. The summer solstice is the date with the longest day and hence with the shortest night. This date usually falls on June 21/ June 22 (in the and -23°27' at the northern hemisphere winter solsticeIn astronomy, the winter solstice is the moment when the earth is in that point of its orbit at which one of the earth's hemispheres is most tilted away from the sun. This causes the sun to appear at its farthest below the celestial equator when viewed fr.
When the projection of the earth axis on the plane of the earth orbit is perpendicular to line linking the earth and the sun, the angle between the rays of the sun and the plane of the earth equator is null. This happens at the equinoxesIn astronomy, an equinox is defined as the moment when the sun reaches one of two intersections between the ecliptic and the celestial equator. The word "equinox" comes from the Latin for equal night . The equinoxes in March and September are the two time. Therefore Sun Dec is 0° at the equinoxesIn astronomy, an equinox is defined as the moment when the sun reaches one of two intersections between the ecliptic and the celestial equator. The word "equinox" comes from the Latin for equal night . The equinoxes in March and September are the two time.
Since the eccentricity of the earth orbit is quite low, it can be approximated to a circle, and Sun Dec is approximately given by the following expression:
if cos operates on degrees if cos operates on radianswhere is Day of the Year, that is the number of days spent since January 1.
The errors caused by this approximation are then contemplated by the Equation of Time.
A diagram demonstrating how the Sun's path over the celestial sphere changes with the varying declination during the year, marking the Azimuths in °N where the sun rises and sets at summer and winter solstice at a place of 56°N latitude.