The one dollar coin circulating denomination (written as $1) was introduced in Australia in 1984, replacing the earlier banknotes. The original reverse design by Stuart Devlin featuring five kangaroos - known in Australia as the "Mob of Roos" design - has not been changed since its introduction.
The denomination is also used by both the Royal Australian Mint and the Perth Mint to issue an extensive range of collector coins, which are legal tender in Australia - such as this one.
In 1922, the eyes of the international scientific community were focused on an expedition of scientists to Wallal, Western Australia to photograph a total eclipse due on 21 September. Precise measurements of the apparent position of the stars near the eclipsed Sun were photographed and provided the evidence supporting Einstein’s revolutionary Theory of General Relativity.
The expedition was organised to conclusively prove Einstein’s theory following the first photographic evidence captured during the 29 May 1919 eclipse expedition led by Sir Arthur Eddington. Teams from multiple countries as well as local astronomers from the Perth Observatory formed the 1922 expedition led by William Campbell from the Lick Observatory (USA), who were successful in taking the images of the eclipse that provided the evidence to support Einstein’s theory.
The theory states that massive objects, such as planets and stars, curve the fabric of space and time around them. The theory predicts that light from a distant star passing near the Sun will follow the curve as it travels to the Earth, making the star appear to be displaced in the sky; it even predicts by how much the stars will appear to be out of place. Normally stars near the Sun are overwhelmed by the bright sky but during a solar eclipse, the Moon obscures the Sun, creating a sky dark enough that stars can be photographed. The Theory of General Relativity predicted the existence of black holes and gravitational waves.
No coins of this type were released into circulation. | 
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