There are many instruments that have been developed throughout history to learn more, to increase observation and research and, ultimately, to improve knowledge on a topic. Thinking back to ancient times, you have to see that before there were not as many facilities to create an instrument as now, so it is quite a feat to create them. For observing the sky and its constellations, an instrument had to be invented to help in the search for them. For this the astrolabe.
In this article we are going to explain what the astrolabe is, how it is used and what types are there.
What is the astrolabe
To get an idea of what technology was before and now, we just have to think that probably thousands and thousands of people were living when the astrolabe was invented but they did not even know of its existence. This is because the media before were not as developed as they are today.
The astrolabe is a star finder to increase the search for the constellations in the sky. With the passage of civilizations, there was more and more interest in the knowledge about the constellations and their meanings.
The classic astrolabes are built with brass and they were only 15 to 20 cm in diameter. Although there were many types of astrolabes, some larger and others smaller, they all retained similar characteristics.
The body of the astrolabe has a mater, a disc with a hole in the center. Thanks to a ring, you can see the degrees of latitude. In the center, we have the tympanum, engraved with circles indicating the altitude. They also have the net, a cut-out disc that serves to observe the tympanum beneath it. At the tips, you can see the number of stars represented. Above the net, we have the index finger that points to the star we are looking at. The alidade is to see how far away the star that has been found is.
Its operation has been truly complex for many users. Manuals hundreds of pages long were required just to operate it. The objective is only spot the star and know its position. It has also served as a navigational instrument to obtain information about the time and latitude at which sailors were located. Furthermore, its use has similarities with other instruments such as the astronomical clock, which has also been fundamental in the measurement of time and astronomical observation.
Operation
The astrolabe works by projecting a celestial sphere with a graduated circumference. It has a needle that rotates around a target where you point the star in question. The purpose of the astrolabe is to be able to measure the angular height at which the star is above the objects on the horizon. Normally, to use this instrument we focus on the star through the straw and another person is the one who reads the string number on the scale to which it is graduated. This means that a single person cannot use this type of instrument, since when we remove our head to look at the mark, we will move from where we see the star.
Another function that has this device is to measure latitudeTo do this, we need to identify one of the stars in the sky and its declination. We obtain this declination from tables. We'll need a compass and an astrolabe. To measure latitude, we use a mathematical formula that varies depending on whether we're in the northern or southern hemisphere. If we're in the northern hemisphere, we'll simply add the star's average altitude and its declination, then subtract 90 degrees. If we're in the southern hemisphere, we'll simply add the star's average altitude and its declination without subtracting anything. To better understand this phenomenon, you may want to learn more about the celestial planisphere, which also makes stargazing easier.
Types of astrolabe
As we have mentioned before, these instruments were created in different types depending on who used it. They were also modified as they adapted to the situations of each moment. His discovery allowed constantly new techniques and materials came out to improve observation and, in turn, other instruments more evolved than the first were created.
We are going to analyze how the main types of astrolabe are alike and how they differ. These had different types of manufacture and materials. However, you will see that all of them have a great influence on the technology we use today and how it facilitated the study of the stars.
Planispheric astrolabe
This model was created in order to be able to analyze the stars at a single latitude. That is to say, know all the stars that are in a certain latitude. To use it, the data and the different planes of the instrument were adjusted to be able to find the stars. If you wanted to carry out another type of observation, you had to adjust all the data again and start from scratch.
It was the simplest instrument to use but the one with the most limitations, since you could only know the stars at a single latitude. Over time, other more sophisticated models were developed that improved the ease of work. A clear example of a simple but effective instrument is the one used in the Prague astronomical clock, which remains a marvel of engineering.
Universal astrolabe
This model evolved with respect to the previous one. It also served to know all the information of all latitudes at the same time. This greatly improved the quality of the observation and of the information obtained through it. It is the most complex device to use and many scientists took too long to learn how to use them. Once its operation is controlled, it can yield great information.
Sailor astrolabe
This instrument was not only used to see what was in the sky but also to orient sailors on the high seas. Seeing that this tool had great potential to guide ships through the sea, a version more adapted to the sea was developed. It was quite useful to know the positions and the latitude at which they were. It is as if it were a navigation system but very primitive.
The only problem it presented was that it was difficult to handle and required long learning.