SIMULATING ANCIENT AND MEDIEVAL ASTRONOMICAL MEASUREMENTS WITH STELLARIUM
All materials are based on the Stellarium software and have been designed by Dr Vassilios Spathopoulos who was generously funded by the Anthony Waterhouse Fellowship scheme of the Institute of Physics, UK. All materials are licensed under a Creative Commons Attribution 4.0.
Observational astronomy is one of the oldest sciences and continues to this day to inspire many people around the world. Nowadays freeware planetarium software such as the popular Stellarium package exist, that can be used to accurately simulate the motion of celestial bodies on a computer. Using the software one can also choose the observation location and date, to obtain a view of the sky from anywhere in the world at any time.
Observational astronomy is one of the oldest sciences and continues to this day to inspire many people around the world. Nowadays freeware planetarium software such as the popular Stellarium package exist, that can be used to accurately simulate the motion of celestial bodies on a computer. Using the software one can also choose the observation location and date, to obtain a view of the sky from anywhere in the world at any time.
By utilising the capabilities of Stellarium, a set of activities is presented that is inspired from historical measurements made in antiquity and the middle ages. These activities are based on observations made by the ancient Greeks, the ancient Babylonians, and the medieval Islamic, Indian and Chinese astronomers, whose contribution to the development of astronomy was immense. Although lacking important observational technology such as the telescope, they performed fascinating naked eye measurements and devised simple but ingenious astronomical calculations. Examples include methods for estimating the difference in longitude between geographical locations using lunar eclipses, the distance to the Moon using a solar eclipse, and determining the correct direction from a specific location to the sacred Islamic city of Mecca.
With the aid of the Stellarium software activity instructions are presented that enable pupils to simulate several of these groundbreaking scientific achievements. The use of planetarium software has the advantage of adding a visual aspect to the procedure thus offering greater realism. Students can therefore closely follow the ingenious methods devised by those pioneers and obtain an understanding of the contribution of ancient and medieval cultures to the development of astronomy.
For a quick preview have a look at the following videos. You can view simulations of some of the measurements performed by the ancient Greeks and observations made by medieval astronomers.
With the aid of the Stellarium software activity instructions are presented that enable pupils to simulate several of these groundbreaking scientific achievements. The use of planetarium software has the advantage of adding a visual aspect to the procedure thus offering greater realism. Students can therefore closely follow the ingenious methods devised by those pioneers and obtain an understanding of the contribution of ancient and medieval cultures to the development of astronomy.
For a quick preview have a look at the following videos. You can view simulations of some of the measurements performed by the ancient Greeks and observations made by medieval astronomers.
Celestial coordinates
No detailed astronomical knowledge is required in order to complete the exercises. It is important, however, to have a basic understanding of the concept of celestial coordinates. In order to know where a celestial body is relative to an observer on Earth, we use a pair of coordinates, the so-called 'horizontal coordinates', 'altitude' and 'azimuth'. Other types of celestial coordinates exist but they are not required for completing these exercises.
No detailed astronomical knowledge is required in order to complete the exercises. It is important, however, to have a basic understanding of the concept of celestial coordinates. In order to know where a celestial body is relative to an observer on Earth, we use a pair of coordinates, the so-called 'horizontal coordinates', 'altitude' and 'azimuth'. Other types of celestial coordinates exist but they are not required for completing these exercises.
Horizontal coordinates: Taken from: By TWCarlson - http://commons.wikimedia.org/wiki/File:Azimut_altitude.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17727911
With the horizontal coordinates, we start by defining the point exactly above our head as the zenith. The root of the word is Arabic as are many of the names still used for stars, due to the great work of the Islamic astronomers of the Middle Ages. The point on the opposite side is the nadir and between the two lies the local horizon. So, as we are standing, we have the horizon in front of us and exactly above us the zenith. Unless you can see through the Earth you will never be able to obtain a view of your nadir. The semicircle that passes through the zenith and also the north and south cardinal points, is the local (celestial) meridian.
The altitude of a celestial body is simply measured from the local horizon in degrees. When it is positive then the observed celestial body is above the horizon and thus can be seen (although those that are low near the horizon are difficult to observe), when it is negative the celestial body is below the horizon and so is out of view. The azimuth is also measured in degrees, usually from the north cardinal point. Thus, a celestial body that is directly to the north of an observer will have an azimuth of zero whereas if it is directly to the south it will have an azimuth of 180 degrees. It remains a trivial task to calculate the azimuth of a body directly to the east and to the west of an observer.
Stellarium software
The software used for all the activities is the freeware Stellarium planetarium package. This can be downloaded from www.stellarium.org. A detailed user manual can also be found there although you only need to read Part I - Basic Use, for the activities presented here. Please also note that you will need to download the full version of the software, the more limited online Web version is not adequate.
To save time, here is a short list of the essential functions that will be needed when completing the activities:
Setting the location: This can be done by pressing the F6 key or clicking on the appropriate icon in the left toolbar to open the Location window. You can then either search for a city or country, use the provided map, or enter the coordinates manually.
Setting the date and time: You can select the Date/Time window from the side bar or by pressing the F5 key. You can also control time by using the J key to slow down or reverse the time increment speed, the L key to increase the speed and the K key to return to normal speed. You can also use the time control buttons in the lower right of the screen.
Navigating the sky: You can press the F3 key to open the Search window and search for a specific object such as the Moon and Sun. You must press the Return key to select the object. You can also use the mouse or arrow keys to look around and the Page Up and Page Down keys to zoom in and out of objects. You can use the left mouse button to select an object, the right button to deselect the object and middle mouse button or the spacebar to center on the selected object.
Measuring angles: The Angle Measure plugin can be used to measure the angular distance between objects. To enable the Angle Measure tool, you must first go to the Configuration Window by pressing F2. You then select Plugins, the Angle Measure and Load at Startup. You must restart Stellarium in order to have this plugin activated.
Opening the help menu: You can press the F1 key for help.
For a good brief introduction to Stellarium you can also take a look at the following video!
With the horizontal coordinates, we start by defining the point exactly above our head as the zenith. The root of the word is Arabic as are many of the names still used for stars, due to the great work of the Islamic astronomers of the Middle Ages. The point on the opposite side is the nadir and between the two lies the local horizon. So, as we are standing, we have the horizon in front of us and exactly above us the zenith. Unless you can see through the Earth you will never be able to obtain a view of your nadir. The semicircle that passes through the zenith and also the north and south cardinal points, is the local (celestial) meridian.
The altitude of a celestial body is simply measured from the local horizon in degrees. When it is positive then the observed celestial body is above the horizon and thus can be seen (although those that are low near the horizon are difficult to observe), when it is negative the celestial body is below the horizon and so is out of view. The azimuth is also measured in degrees, usually from the north cardinal point. Thus, a celestial body that is directly to the north of an observer will have an azimuth of zero whereas if it is directly to the south it will have an azimuth of 180 degrees. It remains a trivial task to calculate the azimuth of a body directly to the east and to the west of an observer.
Stellarium software
The software used for all the activities is the freeware Stellarium planetarium package. This can be downloaded from www.stellarium.org. A detailed user manual can also be found there although you only need to read Part I - Basic Use, for the activities presented here. Please also note that you will need to download the full version of the software, the more limited online Web version is not adequate.
To save time, here is a short list of the essential functions that will be needed when completing the activities:
Setting the location: This can be done by pressing the F6 key or clicking on the appropriate icon in the left toolbar to open the Location window. You can then either search for a city or country, use the provided map, or enter the coordinates manually.
Setting the date and time: You can select the Date/Time window from the side bar or by pressing the F5 key. You can also control time by using the J key to slow down or reverse the time increment speed, the L key to increase the speed and the K key to return to normal speed. You can also use the time control buttons in the lower right of the screen.
Navigating the sky: You can press the F3 key to open the Search window and search for a specific object such as the Moon and Sun. You must press the Return key to select the object. You can also use the mouse or arrow keys to look around and the Page Up and Page Down keys to zoom in and out of objects. You can use the left mouse button to select an object, the right button to deselect the object and middle mouse button or the spacebar to center on the selected object.
Measuring angles: The Angle Measure plugin can be used to measure the angular distance between objects. To enable the Angle Measure tool, you must first go to the Configuration Window by pressing F2. You then select Plugins, the Angle Measure and Load at Startup. You must restart Stellarium in order to have this plugin activated.
Opening the help menu: You can press the F1 key for help.
For a good brief introduction to Stellarium you can also take a look at the following video!
Finally, you can follow an online tutorial on the software hosted by the Open University, here!
