A couple of years ago when the Purana Qila still hosted a sound-and-light show, a friend came back from one such show, impressed with the ambience and almost poetic in his description of the silhouettes of the octagonal Sher Mandal on a full moon night. Such shows have been discontinued and one will have to wait till the electrification work to light up the entire fort is complete so that the monuments inside remain open to the public till 10 p.m. Once that happens, sitting on the steps of the double-storey Sher Mandal under a clear night sky one can imagine the thrill of viewing stars and constellations from the upper floor of this observatory.

In this International Year of Astronomy, it is indeed fitting that the two Jantar Mantars— one in Jaipur and the other in Delhi—have been recommended by the Archaeological Survey of India for the UNESCO list of heritage sites. Meanwhile, a much older observatory, Pir Ghaib, at Hindu Rao in the heart of the northern ridge, stands in neglect. The 14th century hunting lodge and observatory, built by Feroz Shah Tughlaq, was also the centre of action during the Revolt of 1857.

Pir Ghaib is so known for the mysterious feat of a saint who had disappeared from the monument. Two years ago, the Nehru Planetarium had undertaken an investigation to find out the astronomical usage of the historic monument.

A peep into the monument and one can spot cracks on the walls and roof of the room that has a cylindrical pillar coming vertically out of the roof. British writers had often referred to the monument as an observatory and according to the experts from the Nehru Planetarium, the upper surface of the cylindrical pillar was perhaps used as a dial for measuring the azimuth of the Sun or the Moon, by inserting a vertical pole into the small hole at the centre of the circular disk covering the topmost surface of the pillar. Another intriguing aspect is the presence of ventilators to the north and south of the tube on the roof of the monument. Apparently, the cylindrical zenith tube was used for correcting clocks that operated on water, as per a 14th century practice.

At the Old Fort, the 16th century Sher Mandal lies locked. Unlike the Pir Ghaib, its exteriors look quite well-maintained. The red sandstone structure with arches, verandahs, and a central chamber has geometric designs adorning its walls with a pillared and domed pavilion. The upper chamber is cruciform in plan and opens into a verandah through four doors. The structure is on an elevated surface. Built by Sher Shah Suri, it was used as both a library and an observatory by Mughal ruler Humayun.

Coincidentally, both these observatories fell into disuse following tragic happenings. While Pir Ghaib seems to have been frequented till mid-19th century, following the Revolt, from May 11 till early June the ridge was under the control of the sepoys. However, after the Badli Ka Sarai battle, the ridge was occupied by the British and Pir Ghaib was used as an outpost. The heavy battery used by the British during the siege of the city was stationed very close to the observatory and hence, the monument was a witness to some of the bloodiest moments of history.

And as for Sher Mandal, on January 24, 1556, as Humayun discussed with experts the hour at which the Venus was to rise, the muezzin gave the call for prayer. In his hurry, Humayun slipped and fell down headlong over the stairs, trying in vain to clutch the edges of the stone steps. He hit the ground, fatally wounded. It is believed that initially, he was buried at Sher Mandal and later his remains were shifted to his tomb nearby. Sher Mandal was deserted after his death and the Mughal capital shifted to Agra.