Astronomical observations with OHP telescopes

ERCA students have the opportunity to use one of the main European-based astronomical observing facilities: the "Observatoire de Haute Provence"but before a general presentation of astronomy and astrophysics is necessary. Because astronomy is an old science, starting from history is determinant. Observation tools, i.e. telescopes but also data analysis tools, are presented here as they are presented during on-site courses. This paper can be used by students before courses, for a better preparation during observations with telescopes, but also after courses, for better completion of their formation.