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Astronomical happenings in this month: September

17th September 1789

Mimas, the smallest and innermost of Saturn's major moons, is discovered by English astronomer William Herschel using his 40-foot reflector telescope. With a diameter of 396 kilometres, it is not quite big enough to retain a round shape.

At just over 186,000 kilometres from Saturn, Mimas takes only 22 hours and 36 minutes to complete an orbit of the planet and is tidally locked, keeping the same face toward Saturn. Its most distinguishing feature is a giant impact crater, named Herschel, after the moon's discoverer which stretches a third of the way across the face of the moon, making it look like the Death Star from the movie Star Wars. Image from the Cassini Spacecraft Credit: NASA/JPL/Space Science Institute

Ground-based astronomers could only see Mimas as little more than a dot until Voyagers 1 and 2 imaged it in 1980. Between 2004 – 2017 the Cassini spacecraft provided further detailed images during its close approach to the moon.

Mimas was named by John Herschel, William Herschel’s son. The mythological Mimas was a giant who was killed by Mars in the war between the Titans and the gods of Olympus.

14th September 1968

The Russian spacecraft Zond 5 is launched. It was the first spaceship to travel to and circle the Moon, the first Moon mission to include animals, and the first mission to return safely to Earth.

It carried the first terrestrial organisms to the vicinity of the Moon, including two tortoises, fruit fly eggs, and plants. Zond 5 was originally planned to fly cosmonauts around the Moon, but the failures of Zond 1968A and Zond 1968B led the Soviets to send an uncrewed mission instead, from fear of negative propaganda of an unsuccessful crewed flight. Image left: The Zond 5 Descent Module on display at the RKK Energiya museum in Korolev, Russia. Credits: RKK Energiya, National Reconnaissance Office

British astronomer Bernard Lovell, considered to be Britain's top space expert, said the Zond 5 mission showed that the Soviets were ahead in the Space Race. The British Interplanetary Society believed that the USSR would be able to send cosmonauts around the Moon within a matter of months however the Apollo 8 mission launched in December 1968, the first human spaceflight to reach but not land on the Moon, paved the way for future Apollo missions ultimately leading to Apollo 11 when the first humans set foot on the Moon.

2nd September 1988

The Australia Telescope Compact Array is opened by the then Australian Prime Minister, Bob Hawke, as a project for Australia's Bicentennial in 1988.

Situated about 25 kilometres west of Narrabri, NSW, it is an array of six identical 22-metre diameter dishes designed to collect radio waves from space. The dishes sit on a wide gauge rail track so that they can be moved into different arrangements to get the best possible images of the sky.

Since its opening in 1988 it has been upgraded to ensure that it remains at the leading edge of radio astronomy research. The Compact Array is one of the most advanced telescopes of its type and is among the top three telescopes of its kind by both publication numbers and citations.

Image: The band played the theme form StarWars Credit: CSIRO Archive.


15th September 1736 Jean-Sylvain Bailly. French astronomer.

Bailly was one of the first historians of astronomy, writing volumes on the history of ancient astronomy, the development of modern astronomy, and on Indian and Oriental astronomy, all of which were published between 1775 and 1787. He calculated the orbit for the appearance of Halley's Comet in 1759. He participated in the construction of an observatory at the Louvre where he could undertake observations of the then known four satellites of Jupiter.. These and other achievements got him elected to the French Academy of Sciences in 1763.

However, in 1789 he turned to political life becoming one of the leaders of the French Revolution. He served as the mayor of Paris from 1789 to 1791, and was ultimately guillotined during the Reign of Terror.

Portrait by Jean-Laurent Mosnier.

9th September 1878 Joseph Mason Baldwin. Victorian Government Astronomer from 1920–1943.

He was chief assistant at Melbourne Observatory from 1908, acting Director from 1915 and served as the third and last of the Victorian Government Astronomer from 1920 to 1943.

During this time the Observatory's main activity was observation of the Melbourne zone for the International Astrographic Catalogue, published in multiple volumes between 1926 and 1963. Baldwin was responsible for setting up the geophysical observatory at Toolangi, recording the exact time for the time-signal service, and magnetic observations.

Baldwin was President of the Royal Society of Victoria from 1925–26; President, Section A, of the Australian and New Zealand Association for the Advancement of Science from 1930-31 and fellow of the Royal Astronomical Society.

Image: Joseph Baldwin, Royal Society presidential portrait, Credit: Royal Society Victoria.

20th Sept 1910 Dorothy Jean Johnson Vaughan. American mathematician at NASA's Langley Research Centre.

In 1949, she became acting supervisor of the West Area Computers Unit, an all-black group of female mathematicians, making her the first African-American woman to receive a promotion and supervise a group of staff at the Centre.

She was later promoted officially to the position of supervisor. During her 28-year career, Vaughan prepared for the introduction of computers in the early 1960s by teaching herself and her staff the programming language of Fortran. She later headed the programming section of the Analysis and Computation Division at Langley. She retired from NASA in 1971, at the age of 61.

In her final years, she worked with mathematicians Katherine Johnson and Mary Jackson on astronaut John Glenn's launch into orbit aboard Friendship 7.

Vaughan is one of the women featured in the 2016 movie Hidden Figures about the African American women who worked at NASA in the 1960’s during the height of the space race. On the 6th November 2020, a satellite named after her - ÑuSat 12 or "Dorothy", COSPAR 2020-079D of the ÑuSat series - was launched into space.


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