from my original blog on 1/9/19:
I last came here over 20 years ago and enjoyed a night-time tour with the opportunity to look through the great 28″ refractor. Even today, this telescope it still one of the largest refractors in the world. However, its location near London makes for rather poor seeing through light-polluted skies and its role for scientific use has been greatly surpassed by modern reflectors (in their various forms).
This ‘scope was completed in 1893 and remained in service until 1960. Its principal task settled on measuring double star systems.
Measurement of the orbits of binary stars allows their masses to be determined via Newton’s Law of Gravitation- the only way that we can directly measure the masses of stars. Not bad for a 70 year old instrument and Newton’s results from 1687 (first publication year of his ‘Philosophiæ Naturalis Principia Mathematica’ – “the Principia”).