Abstract:
In India, there are extant two nineteenth century specimens of an otherwise unknown astronomical instrument called Shabnumā-wa-Rūznumā with which observations can be done both in the day and at night. While the Rūznumā is nothing but a sine/horary quadrant, the Shabnumā appears to be inspired by the Sanskrit instrument Dhruvabhrama-yantra which was invented by Padmanābha in the first quarter of the fifteenth century in Central India. After a brief description of the Dhruvabhrama-yantra, the two specimens of the Shabnumā-wa-Rūznumā are described in detail.
Machine summary:
com (received: 05/07/2011-accepted: 20/09/2011) Abstract In India, there are extant two nineteenth century specimens of an otherwise unknown astronomical instrument called Shabnumā-wa-Rūznumā with which observations can be done both in the day and at night.
While the Rūznumā is nothing but a sine/horary quadrant, the Shabnumā appears to be inspired by the Sanskrit instrument Dhruvabhrama-yantra which was invented by Padmanābha in the first quarter of the fifteenth century in Central India.
A reverse case of transmission is exemplified by a Sanskrit instrument called Dhruvabhrama-yantra which appears to have inspired the production of the Shabnumā-wa-Rūznumā by the Muslim astronomers of India.
The outermost annulus or circular scale is divided into 60 cells, each of which represents the traditional Indian time unit of ghatī of 24 minutes.
To put it differently, if we divide the circle into 360º from topmost point which indicates the beginning of the 22nd ghatī and number the degrees serially clockwise, then the ghatī scale and all other scales commence from 234º.
It is also reasonably certain that the latter was designed in India by Muslim astronomers who were familiar with the elements of Sanskrit astronomy and calendar, because the Shabnumā-wa-Rūznumā makes use of Indian units of time measurement, viz.
” On the two indices pivoted at the centre, the following labels are engraved, starting from the centre and reaching up to the lower end: (View the image of this page) Method of observation with the Shabnumā A plumb line is suspended from the centre.