Separated by just 18 degrees longitude but over 85 degrees latitude, the Royal Observatories of Greenwich and the Cape were twin institutions whose objectives and outputs were intertwined for over 150 years. In this paper I will summarise and assess how these two locations worked together and used their respective influences to collect data for astrometry, terrestrial magnetism and solar studies across hemispheres.

Firstly, I will consider how new instruments were chosen, shared, tested and replicated between the two observatories, namely through the use of the Troughton Mural Circle (1812) and the Airy Transit Circle (1855). Similarly, the Astronomer Royal at Greenwich was sometimes called upon to offer advice on replacing lost instruments at the Cape, especially those destroyed in the disastrous fire of March 1852.

Secondly, I will consider the exchange of staff between Greenwich and the Cape, many of whom used the opportunity for experience across hemispheres to enhance their chance of promotion when returning to their home institution or similar destinations elsewhere.

Thirdly, I will assess the role of collaborative projects in facilitating the exchange of people and instruments between the two observatories, starting with the daily photographs of the Sun taken at the Cape which were used to complete the gaps in the Greenwich solar photographs on cloudy days.

The disparity in the number of astronomic observatories at the Northern and Southern Hemispheres at the first half of 19th century - in a total amount of 230 observatories, only eight of which were located in the South (HOWSE, 1986) – certainly contributed to transforming the Southern sky into an opportunity for the development of astronomy. The Southern Hemisphere thus constituted a broad and powerful field for astronomical research, especially considering the work on positional astronomy that had already been carried out by observatories in the Northern Hemisphere since the 18th century. In this context, the founding or renovation of the observatories in the South can be understood as a response to that discrepancy. The objective of this paper is to analyze some of the instrumental and practical innovations introduced by the French astronomer Emmanuel Liais (1826-1900) during the 1870s and 1880s, when he assumed the directorship of the Imperial Observatory of Rio de Janeiro (Brazil). These innovations were connected to Liais’s scientific trajectory in France and his scientific practices at the Observatory of Paris. Exploring the connections between the North and the South, the circulation of instruments, people, and scientific practices, a central inquiry posed by this paper is a reflection on the astronomical projects that Liais intended for the Imperial Observatory and the local context and disputes he had to face.

Despite being a northern hemisphere institution (latitude = +42 deg), the Department of Astronomy of the University of Michigan in Ann Arbor has continuously maintained a strong presence in the southern hemisphere for almost 100 years.

In 1928 the Lamont-Hussey Observatory began operation on Naval Hill in Bloemfontein, South Africa. Its 67-cm visual refractor was the largest refractor in the Southern Hemisphere and was used almost exclusively for double star work. Astronomers from Lowell Observatory used the telescope on multiple occasions to photograph Mars at its closest approaches. Lamont-Hussey was closed in 1971, and the telescope subsequently dismantled.

Joining it in 1966 was the 0.6-m Curtis-Schmidt telescope which left its cloud covered home in Michigan to become one of the first telescopes on the new Cerro Tololo Inter-American Observatory in Chile, where it remains today. Science with this wide-field telescope included surveys for quasars, a narrow band survey of the Magellanic Clouds looking for supernova remnants, and searches for supernovae. The southern part of the Michigan Spectral Catalog used objective prism plates taken with this telescope. Beginning in 2001, the telescope was dedicated to a NASA funded survey for orbital debris at geosynchronous orbit.

In the 1990s Michigan joined the Magellan collaboration of two 6.5-m telescopes on Las Companas in Chile. This facility is used by Michigan astronomers for many different research projects.

More recently Michigan became the only US institution participating in the European Southern Observatory’s Extremely Large Telescope (ELT): a 39-meter telescope under construction in Chile.