Latitude by the stars | badz.info
The vertical angle between your northern horizon and the place in the sky where you see Polaris is very nearly the same angle as your north latitude. Let us remind about the definition of Geographical Latitude "G.L.": The North Star Polaris is to the upper right. In any math book - you may find drawings like. It turns out that your latitude is the angle at which Polaris appears to sit above the horizon. makes with the plane containing the equator.
- Use the Altitude of Polaris to Find Latitude
- What is the relationship between Polaris altitude and someones latitude?
- Final Event - The Polar Star.
Crude instruments to obtain this angle have existed for thousands of years and by the time of Lewis and Clark, instruments like the sextant and octant, only slightly less precise than those available to us, were in use. Figure 1 shows graphically what an ephemeris shows in tables. The difference is that the astronomical almanac gives figures for solar sunlunar moonand astral star altitudes for every day of the year along all lines of latitude whereas the diagram indicates only solar altitude at 4 times during the year equinox and solstice and only along one line of latitude.
What line of latitude? That can be determined from the diagram below as follows: To use the ephemeris, all one needs to know is the day of the year and the altitude of the sun, the moon, or one of the key stars such as Betelgeuse, Aldebaran, Antares, or Vega. Latitude may also be calculated by measuring the altitude of the sun, moon, or certain planets and stars above the horizon on known days and reading latitude from tables designed for that purpose.
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.
Latitude by the 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.How to Determine Your Latitude Using Celestial Observations
This device allowed him to measure the "altitude" of Polaris or the North Star. This angle is called "the altitude" of Polaris.
For any point between the Equator and the North Pole, latitude is obtained simply by measuring 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.
Longitude Figure 3 Longitude and Time For 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, inHarrison had a working chronometer, durable enough for extensive field observation.
It was a version of this chronometer that Lewis and Clark carried with them.
Put in another way - the North Star Polaris will be placed high on the sky when viewed from the Arctic 90o from the Pole: Click to obtain larger figure GIF, 35k.
Some history During the Middle Ages, every Christian man with self-respect should visit Jerusalem at least once during his life.
Bishop Nicolas from Iceland published a method to determine the altitude of the North Star and thereby to determine the geographical latitude in Click to obtain larger figure JPG, 85k This method works the following way: Lie down on the ground and put your right hand above the knee, as shown on the picture.
What is the relationship between Polaris altitude and someones latitude? | Yahoo Answers
When the North Star is right above your thumb, then you have arrived at the latitude of Jerusalem. Another exercise Measure the altitude of the Polar Star Now we are ready to measure the height of our polar star ourselves. There are several ways to do this, first of all by means of the astrolabium - an instrument applied by Columbus during his voyages to America: A simple astrolabium - based on what you may find in any school Measure the height of Polaris applying the equipment above.
You merely have to point the long side of the triangle towards the Northstar.
Astronomy On-Line: Measuring the Altitude of the North Pole Star
Having done this, put a finger on the seewing thread and move into your house. Standing in clear light, read the number and write it down.
Not all explorers applied the astrolabium, some applied the Jacobian Stick: The Jacobian Stick Construct such a device and calibrate it. Ask your math-teacher how to do so. The Jacobian device had the disadvantage of being a bit clumsy - it is difficult to keep an eye on both a star and the horizon. If you construct this instrument - beware - don't fall while you are aiming it out in the dark!