The location of buildings across the Observatory site was a direct outcome of the scientific requirements of the work being undertaken.
When Melbourne Observatory opened in 1863, all the astronomical functions of the Observatory were initially gathered in the main building, including the transit telescope, equatorial telescope and prime vertical telescope. However the sensitive magnetic instruments needed to be kept way from any other metal objects that might disturb the measurements. The instruments were kept in two separate magnet houses, the Absolute House and the Horary House, both some distance from the main Observatory building, and separate from one another. The meteorological instruments were also kept in a separate cluster to the east of the main building, so that the air could circulate freely around the thermometers.
The location of additional buildings and structures was also dictated by scientific and astronomical considerations. Transit telescopes could be attached to the main building as they only had to have line of sight in one plane; thus new transit rooms were added to the main building in 1866 and 1883. New equatorial-mounted telescopes were placed elsewhere on the grounds so that they could have clear views at lower altitudes; attaching them to the main building would have added considerably to the costs, as they would need to be raised higher to give them a clear view over the main building's roofline. The Astrograph could be relatively close to the main building to its north, because its allotted task was to photograph stars towards the south celestial pole.
The location of the Great Melbourne Telescope some distance from the main building was dictated by the concern that it should be removed as far as possible from the existing magnet houses on the south and west of the site, to reduce the chance of the large metal telescope, lenses and associated machinery interfering with the magnetic observations. Its location to the north of the site also gave it clear lines of sight in most directions, except for its own roll-back roof to the south.
Timeline of Main Buildings
Absolute Magnet House, 1861
Horary Magnet House, 1861; demolished & replaced by Differential Magnet House, 1867
Main Observatory Building, 1861-1863
Astronomer's Residence (original), 1861; demolished 1914
Assistant Astronomer's Residence, 1861; demolished 1914
Second Transit Room added to Main Building, 1866
Differential Magnet House, 1867; demolished & replaced by Magnet House, 1877
Great Melbourne Telescope House, 1869-1870
Thermograph House, 1870; demolished
Photoheliograph House, 1873
South Equatorial House, 1874
Magnet House, 1877
Thermometer Shed, 1879; moved 1885; demolished
East Transit Room added to Main Building, 1883
New Workshop added to Great Melbourne Telescope House, 1888
Astrograph House, 1889
Astronomer's Residence (new), 1889
Computing Room added to Main Building, 1892
Caretaker's Quarters, 1902
Astrophotographic Room added to Main Building, 1902
Strong Room added to Main Building, 1902
Whirling Room added to Great Melbourne Telescope House, 1904
Anemometer Tower, 1906