This page brings together activities related to visual observation :

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  • Locating the “horsehead” nebula in visual observation
    It is one of the most famous objects, highly prized by astrophotographers, yet very difficult to detect and appreciate visually. And for good reason: it is a dark nebula, a cold molecular gas cloud that emits no light in the visible spectrum. Observing it relies on a “stroke of luck”—the fact that this nebula is in the foreground relative to a hydrogen cloud, which reflects the result of its own ionization back to us. Consequently, the nebula becomes visible, in a way, “backlit”. But even so, the background cloud emits in deep red, a wavelength to which the human eye […]