(Updated, June 2022). The artist’s viewpoint is from the south-south-east, roughly in front of the entrance to the late-19th-century South Building. Modern Blackheath Avenue would be to his right, where the ground is also more level than shown. Notable features include the tall chimney of the rear extension to Flamsteed House that was added under James Bradley as 3rd Astronomer Royal,1742-62. His extension was demolished in 1789 and replaced by a larger one (with two tall chimneys) by Nevil Maskelyne, 5th Astronomer Royal, 1765-1811. The two-storey building with a classical pediment is Bradley’s ‘New Observatory’ of 1749 comprising a ground-floor computing room with an assistant’s quarters above and two single-storey wings holding a quadrant room to the west and Bradley’s transit room to the east: the roof of the latter is shown open for transit observations on Bradley's Greenwich Meridian, established in 1750 (about 6 metres west of Airy's, the current Prime Meridian of 1851).

The image dates to after 1779 since the so-called ‘Advanced Building’ – the one with the sloping (and opening) roof was built to contain new instruments in that year, south of Bradley’s quadrant room and as an upward extension of John Flamsteed’s 1670s sextant house: neither now survive. The side windows of Flamsteed House are also inaccurately shown as three panes wide when in fact they had four and were vertical-opening upper and lower casement pairs from 1779 until changed to single sashes in 1790. The vent-like finial on the west turret is the rotating lens of the camera obscura that Maskelyne installed there by 1778.

The domed building at left seems to be at the south-west corner of Bradley’s Flamsteed House extension but this is owing to misleading perspective. It is in fact the western summerhouse on the Observatory’s north terrace, though it may not have been so fully visible from the artist’s apparent viewpoint. Its eastern pair is hidden by Bradley’s New Observatory. In 1773 Maskelyne raised the height of the summerhouses and extended them south, adding hemispherical domes and upper horizontal windows (of which one is shown here). The domes opened to observe comets using a pair of equatorial sectors installed under them.

The pitched-roof building at lower left (in fact more square than rectangular) is the 1670s ‘Garden House’ used as a stable through the 18th century, with sloping access up to the gate shown in the perimeter wall: it is today a flat-roofed, two-level plant room. The other shed, apparently wooden, is undocumented and probably for an associated purpose. The foreground shows former sand and gravel workings on the south-west and south side of the hill, now a partly terraced garden area. This early quarrying had stopped when the Observatory was built in the 1670s, or very soon after.

The drawing arrived, originally on loan to NMM from the Royal Greenwich Observatory (RGO), in a rather damaged gilded wooden frame. It may be the image of the Observatory that is second on a list of a dozen pictures, formerly belonging to Nevil Maskelyne, that his wife presented to the Observatory and left at Flamsteed House when she moved out in 1811, following his death. When the RGO closed in 1998, ownership of this and other items belonging to it was transferred to the Museum. See ZBA0692 for further details.