History

When Plaskett answered his question affirmatively, events moved with astonishing speed, and the idea was presented to the House of Commons later that year. Moreover, from the beginning of this project, the Isaac Newton Tercentenary Committee (he was born in 1642 but WWII postponed 1942 activities) had been involved and would name the telescope in his honor.

The primary mirror was a Pyrex blank cast by Corning in the USA in 1936 and was already roughly ground. It was originally intended for a telescope at Michigan State University and was donated to UK in 1949 by the McGregor Foundation. However, it took over a decade for a design to be finalised and for funding approval; fabrication of the mirror was taken over at Grubb Parsons in UK 1959. With first light in 1965, it was dedicated in 1967 by the Queen, it began its service at Herstmonceux (East Sussex, UK); that site was determined by the relocation of the Greenwich Observatory telescopes in the 1950s.

The classical Cassegrain had a 2.49-m f/3 parabolic Pyrex primary mirror; there was an observer’s cage and camera at prime focus. The cage could be swapped with an 0.5-m secondary with an f/14 Cassegrain focus or another secondary with an f/32 Coud&eeacute; focus one floor below the telescope. It was carried on an equatorial fork mount which was supported by a pier 15 m above ground level.

Important work was done in astrometry and spectrometry for 14 years at Herstmonceux; it stimulated the development of a deep cadre of astronomers that was ready to move on to a darker, drier, higher environment. Eventually, the marginal conditions in Sussex, the advent of affordable air travel, the benefits of a high mountain top site, and the success of other international consortia led the INT's management to transplant it to La Palma in 1979, but after a slightly larger, 2.54-m f/3.29 Zerodur primary from Grubb Parsons and a new mount were installed, it was hardly the same telescope! The two secondaries provide f/15 Cassegrain and f/50 Coud&eeacute;.

The mechanical structure of the INT was shipped to La Palma in 1981 and was re-erected into the bare frame of its building in 1982. The mirror arrived on the island on December 10, 1982; the building was handed over by the contractors to the RGO on January 17, 1983 and work began on preparing the laboratories and workshops for the commissioning of the telescope. The first of three direct air shipments of machinery, instruments and computers arrived on La Palma on January 25. By September the building was in full operation and the telescope was fully assembled, with a freshly aluminised mirror, by the end of the year. On the first night of February 1984 stars were first seen in the telescope, at the prime focus. The telescope commissioning programme had been targeted towards the completion of the Cassegrain spectrograph since this would be the most widely demanded instrument; it was also tolerant to telescope pointing and tracking.

In the spring of 1984 there was a concentrated effort to commission the Cassegrain instrumentation, including acquisition TV cameras, Intermediate Dispersion Spectrograph (IDS), IPCS and CCD detectors and ADAM, the software environment which brings together this complex of instruments into one working station. This programme was completed in May.

On May 29 1984, the telescope welcomed its first scheduled astronomer. It operated for astronomers for 47% of the time in the first six-month period (Semester F), 50% in semester G, 62% in Semester H and 73% in Semester I. The rest of the time was used for engineering work.

The born-again INT at La Palma, differs significantly in its mechanics, electronics and optics from the earlier incarnation at Herstmonceux: The change in latitude from 50 degrees 51 minutes 58 seconds to 28 degrees 45 minutes 43.4 seconds resulted in a large change of angle to the polar disc which stands almost on edge. A segment was removed from the disc in order to allow operation to a declination of -30 degrees.