On 9 December 1874 a rare astronomical event occurred – the transit of Venus.  This involves Venus passing directly between the Earth and the Sun.

The Government Astronomer of the day (Henry Chamberlain Russell) decided that NSW would take a major role in the observation of this rare event.   Senior scientists of the NSW establishment took part in the observations which involved accurate timing of the entry and exit of the disk of Venus upon the Sun’s disk.   The observations involved timing four contacts where the leading and trailing edges crossing the sun were timed.   The aim of the observations was to enable calculation of the length of the Astronomical Unit (the distance between the Sun and the Earth)

Observations were carried out at various places throughout NSW – at Bega on the far south coast, Goulburn in the Southern Tablelands and Woodford in the Blue Mountains.  The most extensive observations were carried out at Sydney Observatory and included sketch images of the entrance and exit of Venus’s silhouette on the face of the Sun

Henry Chamberlain Russell achieved a grant from the NSW Government which he used to purchase the South Dome Refractor at Sydney Observatory.  Thus it can be said that the South Dome Refractor is also 140 years old and reputedly the oldest telescope still in use in Australia.  As such it is a major museum piece and is popular with members of the public for viewing the moon, bright planets and stars.

Inside Sydney Observatory there is an exhibition about this important 1874 transit of Venus. You can see this for free entry 10am to 5pm daily or on your booked night tour.

This post was written by astronomy guide and engineer, Col Draper. You can meet Col on a guided daytime tour at Sydney Observatory.