At the inauguration of the sculpture in the Market Place the sculptor explained what it represents but I expect many people who were not there will still be puzzled.
An orrery is a clockwork brass model of the solar system to illustrate how the planets travel at various speeds and distances from the Sun. They were popular in the 18th century.
The Grantham ‘Orrery’ takes the Market Cross as the position of the Sun and the sculpture depicts the Earth as a shiny globe on a tall column with the smaller Moon attached. The large yellow globe at a lower level represents the planet Venus whose orbit is somewhat nearer the Sun. A brass disc inserted into the paving nearby seems to illustrate the phases of the Moon.
Perhaps an explanation on these lines, together with something about the ‘Newton connection’, could be given on an information board similar to the one The Civic Society has already put in place by the Conduit.