Many instruments have been developed throughout history to learn more, to enhance observation and research, and ultimately, to improve our understanding of a subject. Looking back to antiquity, it's important to remember that creating instruments wasn't as easy as it is now, making their invention a remarkable feat. For observing the sky and its constellations , an instrument had to be invented to aid in their identification. This led to the invention of 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 used to aid in locating constellations in the sky. Throughout history, civilizations have shown increasing interest in understanding the constellations and their meanings.
Classical astrolabes were made of brass and were only 15 to 20 cm in diameter. Although there were several types of astrolabes, some larger and some smaller, they all shared similar characteristics.
The astrolabe's body has a reticle, a disc with a hole in the center. A ring allows you to see the degrees of latitude. In the center is the tympanum, engraved with circles that indicate altitude. It also has a rete, a cut-out disc used to view the tympanum from below. The number of stars represented is indicated at the corners. Above the rete is the index, which points to the celestial body being observed. The alidade is used to measure the distance to the located star.
Its operation has been quite complex for many users. Just to use it, manuals of hundreds of pages were needed. The objective is simply to spot the star and determine its position . It has also served as a navigational instrument, providing information about the time and latitude of sailors. Furthermore, its use is similar to other instruments such as the astronomical clock , which has also been fundamental in timekeeping and astronomical observation.
Operation
The astrolabe works by projecting a celestial sphere onto a graduated circle. It has a needle that rotates around a sighting point where you fix the star in question. The purpose of the astrolabe is to measure the angular height of the star above objects on the horizon. Normally, to use this instrument, one person focuses on the star through the eyepiece, and another reads the corresponding number on the graduated scale. This makes it unsuitable for a single person to use, since moving their head to read the mark would shift their position from the star.
Another function of this instrument is to measure latitude . To do this, we need to identify a star in the sky and its declination. We obtain this declination using tables. We will need a compass and the astrolabe. To measure latitude, we use a mathematical formula that varies depending on whether we are in the Northern or Southern Hemisphere. If we are in the Northern Hemisphere, we simply add the average altitude of the star and its declination, then subtract 90 degrees. If we are in the Southern Hemisphere, we simply add the average altitude of the star and its declination without subtracting anything. To better understand this phenomenon, you might want to learn more about the celestial planisphere , which also facilitates stargazing.
Types of astrolabe
As we mentioned earlier, these instruments were created in different types depending on who used them. They were also modified as they adapted to the situations of each era. Their discovery led to the constant development of new techniques and materials to improve observation , and in turn, to the creation of other, more advanced instruments.
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 to analyze stars at a single latitude. In other words, to identify all the stars located at a given latitude. To use it, the data and the instrument's various planes were adjusted to locate the stars. If a different type of observation was desired, all the data had to be readjusted and the process started from scratch.
It was the simplest instrument to use but also the most limited, since it could only observe celestial bodies at a single latitude. Over time, more sophisticated models were developed that improved ease of use. A prime example of a simple yet effective instrument is the one used in the Prague Astronomical Clock , which remains an engineering marvel.
Universal astrolabe
This model was an evolution of its predecessor. It could also gather information from all latitudes simultaneously. This significantly improved the quality of the observations and the data obtained. It is the most complex instrument to use , and many scientists took a considerable amount of time to learn how to operate it. Once its operation is mastered, however, it can provide a wealth of information.
Sailor astrolabe
This instrument was used not only to see what was in the sky but also to help sailors navigate at sea. Seeing its great potential for guiding ships, a version better suited to the marine environment was developed. It was quite useful for determining position and latitude. It's like a very primitive navigation system.
The only problem it presented was that it was difficult to handle and required long learning.
