At the north pole what is the altitude of polaris

But our blanket of air refracts starlight, causing an object near the horizon to appear higher than it really is. Under typical atmospheric conditions, this adds 0. In 12, years, Polaris will reach its lowest declination of At that time, Polaris will be visible anywhere north of Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter.

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Due to its remoteness, inhospitable weather conditions and lack of natural land bridges connecting it to other continents, Antarctica has spent the last 35 million years in relative silence and seclusion. Prior to its discovery in , no humans had ever set eyes on this icy continent. It was not much more difficult for the captains to measure these altitudes with a sextant or octant and to calculate latitude using one of the three ephemerides or astronomical almanacs they carried.

These contained tables showing the daily position of celestial bodies such as the sun, the moon, and key stars. Calculating latitude gave Lewis and Clark few problems and their readings were accurate to within a fraction of a degree.

In Figure 2, an illustration from a 16th century portolan atlas, a seaman is determining latitude using a cross-staff. This device allowed him to measure the "altitude" of Polaris or the North Star. This angle is called "the altitude" of Polaris. Before the use of the cross-staff pictured, mariners and others who needed to determine latitude used flat pieces of wood with holes to sight through to locate Polaris and with pieces of cord attached to measure angles.

F or much of the early era of global exploration, longitude had been difficult to calculate because either an elaborate set of astronomical tables and measurements were required or an accurate time-keeping device was necessary, and neither was available until the 18th century.

As early as Galileo had devised a way to determine longitude by observation of the passage of the 4 moons of Jupiter. By the early 18th century, while still using the transit of Jupiter's moons, navigators had learned to make approximate calculations of longitude by observing the changing angular distance between the Moon and a prominent star such as Antares.

But numerous careful observations and extensive calculations were required for this method to work and neither of these was really feasible on board ship or in the field. Numerous sea trials and several improved versions of Harrison's original model were required before, in , Harrison had a working chronometer, durable enough for extensive field observation. It was a version of this chronometer that Lewis and Clark carried with them.

All this seems quite simple. Why, then, were the captain's longitudinal observations so prone to error? South of the equator, Polaris drops out of the sky. When the North Star Polaris appears 5 degrees above the horizon, it means that the observer is 5 degrees latitude north of the equator.

From this, we can see that, in the northern hemisphere, the altitude of the Pole Star corresponds to the latitude of the observer. Begin typing your search term above and press enter to search.