Among the devices that were used for orientation in time and space from the early ages - apart from the sundial, the oldest instrument for time measurement - are the compass and sextant as well as simple telescopes. The Sundial was made by the very early cultures in Egypt and Mesopotamia.
The so-called shadow clock, also called the gnomon, is among the oldest clocks ever. It was used as early as 3500 BC. A sundial consists of a vertical stake pushed into the ground, which throws a shadow. Owing to the rotation of the Earth about its axis the shadow that is thrown by the sunlight changes. In the morning, if the incident light falls at a big angle the shadow becomes very long.
As the Sun rises higher, the shadow becomes shorter. As the Sun moves in the sky, the direction of the shadow that the stake throws also changes. The time of day can be indicated by markings for the shadows on the ground. Sundials were used to measure time till into the Middle Ages. In China, time was measured without sunlight.
A cord with knots in it was ignited and the time that the fire needed to go from one knot to the next was taken as a unit of time. The ancient Greeks (Hipparchos) invented the astrolabe for determining the position of celestial bodies.
It could be used to calculate the rising and setting of the stars and their location in the sky at different times. In the 16th century, a Danish astronomer called Tycho Brahe built a device with a diameter of 3 meters, with which he made accurate observations of the solar system.
Up until the 18th century, the astrolabe was also important for navigation as well. The astrolabe was a vertically suspended circular disk with a movable frame. The brightest stars were defined on the frame. By turning the frame, the astronomer could simulate the movements of the stars.
To determine the height of a star, a sighting beam was aligned with the star. A so-called Jacob's staff was used for measuring angles in astronomy, for the purpose of orientation in space. It could be used to measure the height of the stars as well as locations at sea.
It was a simple device, consisting of a longitudinal rod with a scale and a lateral rod that was fixed at right angles to it, and which could be moved. If measurements were to be carried out on a star, it was viewed over the end of the longitudinal rod and the lateral rod was moved till the star was covered by the lateral rod.
The Jacob's staff was the forerunner of the sextant. The compass was used for determining directions. It existed in a simple form as a magnetic compass since the 13th century. It is mainly used in maritime navigation, as well as on land.
Two compass variants were developed further at the start of the 20th century: the magnetic compass, which was, of course, well-known, and the gyrocompass. The first telescopes for observing the sky existed in the 17th century.
In 1608, the Dutch spectacle-maker Hans Lippershey developed the first telescope. However, some scientists have their doubts about this date. However, it is certain that Galileo Galilei built his first telescopes in the year 1609. Using them, he discovered, among other things, the four largest moons of Jupiter, the unevenness of the lunar surface, sunspots and so on.
The first reflecting telescope was developed in the year 1668 by the English physicist Sir Isaac Newton . In contrast to the old telescopes that used a lens to collect the light and another for viewing the enlarged image, reflecting telescopes had a concave mirror to collect the light. In 1672, a French astronomer, G.D. Cassegrain, invented a reflecting telescope in which he used a convex mirror. W.F. Herschel later made improvements to it.
