## The horizon

*Designed and produced by the Spanish CoI*

The c-book unit «The Horizon» was designed by five members of the Spanish CoI. This c-book unit is devoted to the study of the vision of the horizon. Some geometric and algebraic basic concepts provide the necessary tools to understand how the height of the point of vision and of the object one tries to see and the radius act on the vision. Furthermore, refraction makes possible to see things beyond the horizon (under the line of vision).

The c-book unit is structured in three phases. The first phase wants to give an answer to the question *Q1: What is the line of the horizon? Which factors may affect in setting the horizon?* The phase begins with some basic questions about the intuition of the students before starting with the main aims to study in this c-unit: Which is the distance to the horizon from the seashore? How does the use of binoculars or similar tools help to the vision? How would the horizon be in the case that the Earth was a plane?. The second phase focuses on *Q2: Which is the distance to the horizon from a certain altitude?* Students are asked to do some forecasts and calculations in order to compare the distance to the horizon from different altitudes, as well as the growth of the distance when the altitude increases. Finally, the third phase is devoted to *Q3: Is it possible to see beyond the horizon?* A picture of watching some mountains in Majorca from a certain point in Barcelona opens this phase, then students are asked about how it is possible to see further the line of the horizon. Then, students are asked to investigate and simulate other possible cases to understand this situation.

Available at: http://mc2dme.appspot.com/dwo/dwo.jsp?profile=78&language=en&courseViewNr=5186321119182848