Civil Engineering ⇒ Topic : Astronomy
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Astronomy
2. The Zenith : The point on the celestial sphere above the observer's station is known as the Zenith. 3. The Nadir : The point on the celestial sphere exactly below the observer's station is known as the Nadir. 4. The Zenith-Nadir line : The Zenith, the observer's station the centre of the earth and the Nadir all lie on a line which is known as Zenith Nadir line. 5. The celestial horizon : The great circle of the celestial sphere obtained by a plane passing through the centre of the earth and perpendicular to the Zenith-Nadir line is known as the celestial horizon. 6. The visible horizon : The small circle of the earth which is obtained by visual rays passing through the point of observation is known as visible horizon. 7. The sensible horizon : The small circle which is obtained by a plane-passing through the observer's station and tangential to the earth's surface and perpendicular to the Zenith-Nadir line at the point of observation is known as the sensible horizon. 8. The terrestrial equator : The great circle of the earth the plane of which is perpendicular to its axis of rotation is known as the terrestrial equator. 9. The terrestrial poles : The points at which earth's axis of rotation meets the earth's surface, are known as the terrestrial poles. 10. The celestial poles : The points at which earth's axis of rotation on prolongation on either side meets the surface of the celestial sphere are known as celestial poles. 11. Vertical circles : The great circles of the celestial sphere passing through the Zenith and Nadir are known as vertical circles. 12. The observer's meridian : The vertical circle which passes through Zenith and Nadir of the station of the observation as well as through the poles, is known as observer's meridian. 13. The prime vertical : The vertical which is perpendicular to the observer's meridian and passes through the east and west points of the horizon is known as the prime vertical. 14. North and south points : The projections of the elevated north and depressed south poles on the horizon are known as north and south points respectively. 15. East and west points : The points on which the prime vertical meets the horizon, are known as east and west points. These points may also be obtained by the intersection of the equator and horizon. 16. Ecliptic : The great circle of the celestial sphere which the sun appears to describe with earth as centre in the course of one year, is known as ecliptic. 17. Altitude : The angular distance of a heavenly body above the horizon, measured on the vertical circle passing through it, is called altitude. 18. The azimuth : The angle between the observer's meridian and the vertical circle passing through the celestial body and the Zenith is known as azimuth. 19. The celestial latitude : The arc of a great circle perpendicular to the ecliptic, intercepted between the celestial body and the ecliptic is known as the celestial latitude of the body. 20. The celestial longitude : The arc of an ecliptic intercepted between the great circle passing through the point of Aries (y) and the great circle passing through the celestial body is called celestial longitude. 360° of longitude = 14 hours of time | |
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