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  • Elizabeth Cocking

In this month: July 2019

5th July 1687

The book Principia is published by Sir Isaac Newton. Written in Latin with the title Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) it is often referred to simply as the Principia. The book contains Newton's laws of motion, Newton's law of universal gravitation and a derivation of Kepler's laws of planetary motion. The Principia is considered one of the most important works in the history of science.

20th July 1969 (or 21st July if you are in Australia)

The Eagle has landed! Astronauts Neil Armstrong and Buzz Aldrin from the Apollo 11 NASA space mission landed on the Moon in the Eagle Lunar Module. Neil Armstrong's famous words ""That's one small step for a man, one giant leap for mankind" were heard around the planet. Michael Collins remained orbiting the Moon in the Columbia Space craft. See our Events page for the 1 July special talk to commemorate this event. Image above courtesy NASA.

23rd July 1995 Comet Hale-Bopp is discovered. Discovered separately by Alan Hale and Thomas Bopp the comet was visible to the naked eye for a record 18 months, twice as long as the previous record holder, the Great Comet of 1811. Accordingly, Comet Hale–Bopp was dubbed the Great Comet of 1997. It is next expected to visit Earth around the year 4380.

1st July 2004

The Cassini spacecraft enters orbit around Saturn. Launched on the 15th October 1997 the Cassini mission was a collaboration between NASA, the European Space Agency and the Italian Space Agency to send a probe to study the planet Saturn. After 20 years in space, 13 of those years exploring Saturn, Cassini exhausted its fuel supply and, to protect the moons of Saturn that could have conditions suitable for life, the spacecraft was intentionally plunged into Saturn’s atmosphere on the 15th September 2017, returning scientific data to the very end.


23rd July 1773 Sir Thomas Brisbane. British Army officer, and astronomer. He was the Governor of New South Wales from 1821 to 1825 during which time he built an observatory at Parramatta. The Parramatta observatory recorded stars of the southern hemisphere, the first detailed observations from Australia.

31st July 1911

Harley Wood. Australian astronomer. NSW Government Astronomer and Director of Sydney Observatory 1943-1974. He made significant contributions to the field of astrometry. During his time at Sydney Observatory he worked on the preparation of the Astrographic Catalogue. He was at the forefront to gather Australian astronomers together into a professional organisation becoming the first President of the Astronomical Society of Australia.

4th July 1973 Bryan Gaensler. Australian astronomer and former Young Australian of the Year, (1999). Currently based at the University of Toronto. He is internationally recognised for his work on dying stars, interstellar magnets and cosmic explosions. His popular astronomy book "Extreme Cosmos" was published in 2012.

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