One involved an assassination attempt in 1877 against Henry Chamberlain Russell, the NSW government astronomer and meteorologist, who ran the site for decades.

As the Sydney Morning Herald reported in an obituary for Russell published after his death in 1907, the "dreadful attempt" involved a parcel containing a ginger beer bottle filled with gunpowder and nails that failed to explode.

"The perpetrator of the outrage was never discovered, but the affair created a profound sensation at the time," the newspaper reported.

One book has speculated the attacker may have been "a disappointed pastoralist" unhappy with Russell's forecast for drought-breaking rainfall that didn't arrive.

But while Sydneysiders have had occasion through the decades to curse inaccurate predictions, such a spur was an unlikely motivation for the would-be bomber.

Instead, Russell's "stormy" relations with staff, including one George Faithful, who defied a ban and brought a "stringy greyhound and smelly goat" to work, may have been the spark, according to a book review carried by the Canberra Times in 1979.

Observatory Hill had only published Australia's first weather map - carried in the Herald - a few months before the bomb plot and they didn't become a daily fixture until 1888, when Russell was confident enough about their utility.

Shifting sites

Come next March, Observatory Hill will have served the city for 160 years. Initially established primarily for astronomical readings, the site's daily gathering of data - especially heat, humidity and rainfall - provides one of Australia's longest-running records of weather and climate.

That record may take a minor jolt next year, when the meteorological instruments will be forced to relocate to make room for the expanding Fort Street Public School next door.

To minimise the disruption, replacement instruments are already in place - about 150 metres north, within the Observatory Hill compound - and are now being tested to ensure continuity.

"It is one of the oldest continuous sites in Australia," says Linden Ashcroft, a climatologist with the Bureau of Meteorology and an expert in colonial meteorological records. "It's good that the new site is so close to where observations have been taken for [almost] 160 years."

Early days

The need for accurate observations was keenly understood by Britain, which dispatched Lieutenant William Dawes with the First Fleet. The young marine was charged with setting up an observatory on the western edge of Sydney Cove in an area now known as Dawes Point.

"He came over to watch the passage of a comet," Dr Ashcroft says. "He didn't see the comet but he did take some pretty good weather records for us for the first few years."

According to David Day, author of The Weather Watchers, Dawes was described as "highly cultivated, and of great scientific knowledge", who also took time to record the language and customs of the Indigenous inhabitants around what would become known as Sydney Harbour.

Dawes, though, fell foul of Arthur Phillip after initially refusing to take part in a punitive action against the Aborigines following the spearing death of the first governor's gamekeeper, and then publicly declaring his regret for taking part. He was sent back to England and later took part in the anti-slavery movement.

Between Dawes' departure in 1791 and Observatory Hill's creation in 1858, weather records were kept only spasmodically. This included at the Paramatta Observatory (initially, Parramatta had just one "r") that ran from 1821 until 1847.

'Knowing the world'

Astronomy's value to the nascent colony was not just star-gazing: identifying the precise positions of the sun and the moon enabled navigators to determine longitude.

Without reliable chronometers at that time, ships - and residents - also needed a daily reset, which Observatory Hill provided.

"Latitude was quite easy to calculate," says Andrew Jacob, an astronomer and curator for Observatory Hill. "Longitude was always more difficult ... [It] needed an accurate time."

Each day - even now - a time ball is dropped at 1pm at the top of a main tower. At the highest natural point in colonial Sydney, the ball's descent, and accompanying cannon blast at Dawes Point, could be seen and heard far and wide. Only about six such balls remain in operation worldwide.

British staff took daily records of tides and currents, typical winds and other weather at Sydney - as they did across the empire.

"All was written up and fed back to the Admiralty [in England]," Dr Jacob says. "It was all part of knowing the world and how to rule it."

Meteorology's time arrives

The needs of maritime commerce and defence drove some of the demand for greater precision in readings and forecasts.

So, too, did those of Australia's burgeoning population of farmers, who were battling to cope with unfamiliar and highly irregular weather patterns - especially for rain. The First Fleet's early struggles weren't helped by their arrival is what in likely to have been an El Nino year, with unusually dry conditions.

Over the years, Observatory Hill would host a range of odd instruments as astronomy and meteorology became increasingly distinct arms of science.

Henry Russell would go on to win international fame for taking some of the first photographs of stars visible in the southern sky. He would also publish in 1892 an account of his team's work in tracking the transit of Venus across the sun 18 years earlier.

A caption on display at Observatory Hill states scientific reviews were generally positive while noting his write-up was "a little late in coming". Also on display is one of the telescopes used, which remains the oldest working one in Australia.

Russell devised and built some of the devices, such as a tipping bucket gauge that automatically measured rainfall.

A hygrograph used changes in the length of human hair to assess changing humidity, while a glassball sunshine recorder - also on display - burnt a trace on cards to assess the intensity of the sun. The monitoring continued until the German supplier ceased making cards for the device.

Tracking climate change

Observatory Hill's role, though, began to diminish with the establishment of the Bureau of Meteorology in 1908.

The Herald bemoaned its location in Melbourne as "perhaps the worst centre in Australia", certainly compared with Sydney. The Harbour City, it argued, lay "on the central track over which the main atmospheric control systems travel".

Some of the buildings later fell into disrepair - including one in the middle of the Fort Street school. With student numbers rising from 80 in 2011 to an enrolment of 220 in 2018, the school is understandably keen to reclaim it.

Observatory Hill continues to fascinate the public, particularly for evening star-gazing, drawing some 150,000 visitors annually.

The bureau's Dr Ashton says the longevity of the weather records at Observatory Hill may stir less excitement, but they are "so valuable ... and are something that needs to be protected".

"Having consistent observations taken in the same place over a long period of time allows us to really monitor any changes that are occurring in the climate."