Although all the stars, by the rotation of the Earth, seem to shift in the sky, there is one star that stands virtually still in the sky. Polaris. To help you, the rough estimate of the position of the star constellations per season is indicated above.
The sailors of the past navigated with the stars. With a “Jakobsstaf” and later with a “Sextant” they could calculate latitude, measuring the angle between the polar star and the horizon. so they knew at what latitude they were. in the Netherlands, the Polaris is about 51º above the horizon. The Netherlands is about the 51st latitude north latitude.
- The Polaris rises higher in the sky the further north, so it is not useful above 70° North latitude.
The Jakobsstaf or degree stick, is the forerunner on the sextant. In the 17th century, the instrument was used to measure corners. The height of buildings but also the position of the sun relative to the horizon and the distances between stars. Sailors thus determined the latitude at which they stood and thus navigated the world seas.
The instrument is quite simple and consists of a wooden stick with a scale. At right angles to a sliding second stick. It was placed from the end of the stick under the eye and in turn looked at the object whose height was wanted to know and the horizon. By sliding the cross stick until it apparently fits between the two points, one could read the scale distribution on the main stick.
A Sextant is a measuring instrument from the end of the 17th century. It was used to measure the angle of the sun at the horizon. With this information and the specific date and time of the meeting, seafarers were able to calculate the latitude of the race and thus determine their course. This was most accurate at noon when the sun is at its peak.
At night,“polish height”was taken by measuring the height of the Arctic Star. Time is less important.
The sextant consists of a “triangular” metal plate with a round base with a scale in arch degrees. 1/6 part of a circle to be exact. (60°) A movable arm is attached to this plate. There is a mirror on both the plate and the arm. Due to different type of filters and an “eyepiece” the mirrors can be used to look at the sun. By moving the arm over the plate, the scale distribution can be read in the circular base.
Because free view of the horizon is required, the instrument can only be used accurately at sea.
AnOctanthad 1/8 part of a circle (45°). The octant was replaced by the sextant around 1767.
In the southern hemisphere you use the Southern Cross. Pull an imaginary line through the crossline and extend it about 5 times. Then draw an imaginary line from two bright stars that are near the Southern Cross. Where the lines intersect, you can determine the direction of the south as shown in the image.
The southern cross lies in the Milky Way, between the lower point and the left side of “the short beam” lies the coal bag. That’s the largest dark cloud of interstellar gas and dust in the sky. Among the millions of stars of the Milky Way, it stands out.
Think a vertical line between the highest and lowest star “the long beam” of the cross. Where the line hits the horizon lies about the south.