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To return to homeport, he would sail north or south as needed to bring Polaris to the altitude hed observed when he left home, then sail down the latitude.Over time, Arab navigators started tying knots in the string at intervals of one issabah.
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At the North Pole, which is 90 degrees latitude, Polaris (the North Star) is directly overhead at an altitude of 90 degrees.
At the equator, which is zero degrees latitude, Polaris is on the horizon with zero degrees altitude.
In the word "astrolabe" - "astro means star and "labe" roughly translates as to take or 'to find.' The astronomer's beautiful, intricate and expensive astrolabe was the grandfather of the much simpler, easy to use mariner's quadrant and astrolabe.
The mariners quadranta quarter of a circle made of wood or brass--came into widespread use for navigation around 1450, though its use can be traced back at least to the 1200s. The scale spans 90 degrees and is divided into whole degrees.
Arabic astronomer's astrolabe made by Hajji Ali of Kerbala around 1790. It was used to find the time of rising and setting of the sun and the altitude of the sun and selected stars.
Importantly, it was used to find the direction of Mecca for the devout Moslem's morning and evening prayers.
The points where the 2 orbital planes meet are called lunar nodes. Lunar eclipses occur when a full Moon happens near a lunar node, and solar eclipses take place when a new Moon occurs near a lunar node. Partial lunar eclipses can be seen across the night-side of the Earth.
No special equipment is needed to see a partial lunar eclipse.
Earth, coordinates, celestial sphere, latitude, longitude, declination, Greenwich Hour Angle, GHA, equator, meridian, degree, minute, nautical mile, geographic position, altitude, azimuth, sextant, index correction, dip, star, navigation, Sun, morning, evening, sight, Local Apparent Noon, LAN, fix, running fix, estimated position, dead reckoning, assumed position, Nautical Almanac, celestial data calculator, Ho, Hc, Hs, Zn, ship, position, sight reduction, intercept method, altitude-intercept method, Marcq Saint Hillaire Method, Universal Plotting Sheet, line of position, LOP In order to better serve our users and sponsors, access to our online materials requires registration.
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We're sitting here safe and dry in the Science Museum at the University of Coimbra.