Hubble's science instruments act as the astronomer's electronic eyes. Light hits the primary mirror, is reflected onto the secondary mirror and from there passes through a small opening in the primary mirror to the focal plane. The focal plane is the size and shape of a dinner plate and is shared by the scientific instruments which sample light and record the information.
Observers can then study the data at STScI or at their home institutions.
The telescope operates 24 hours a day. However, scheduling is tricky. At certain times of the year a celestial object may not be visible because it appears too close to the Sun. Furthermore, Hubble is not in constant communication with the ground stations. Consequently, technicians must plan each observation down to the second, telling the telescope what to do and when, using detailed computer-coded instructions transmitted to and stored inside the telescope's onboard computer.