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  • Elizabeth Cocking

In this month: October 2021

10th October 1846

Triton, the largest natural satellite of Neptune, is discovered by English astronomer William Lassell. The image of Triton below is courtesy of NASA/JPL/USGS.

The discovery comes only seventeen days after the discovery of the planet itself. With a diameter of 2,710 kilometres it is the seventh-largest moon in the Solar System and is one of the few moons in the Solar System known to be geologically active, as a consequence, its surface is relatively young with few obvious impact craters. It has a surface of mostly frozen nitrogen, an icy mantle and a substantial core of rock and metal. During its flyby in 1989 Voyager 2, the only spacecraft to visit Triton, found surface temperatures of −235 °C and also discovered active geysers.

29th October 1991

The Galileo spacecraft, on its way to Jupiter, comes to within 1,600 kilometres of the asteroid Gaspra making it the first ever asteroid to be visited by a spacecraft. The image below of asteroid 951 Gaspra is a mosaic of two images taken by the Galileo spacecraft from a range of 5,300 kilometers (3,300 miles), some 10 minutes before closest approach on October 29, 1991, credit NASA/JPL/USGS. Gaspra, an S-type asteroid, is an irregular body of about 20 x 12 x 11 kilometres. Its surface reflects approximately 20 percent of the sunlight striking it. It orbits the Sun at an average distance of about 330,000,000 kilometres and completes one orbit around the Sun in 3.29 years. Gaspra rotates in a counter-clockwise direction in just over 7 hours.

23rd October 2013

The Planck Space Observatory is turned off.

Launched on the 14th May 2009 by the European Space Agency its mission was to scan deep space for the faint cosmic microwave background, the oldest light in the universe created 380,000 years after the Big Bang. Its original target was to complete two whole surveys of the sky, but Planck ended up completing five full-sky surveys. In January 2012 the High Frequency Instrument (HFI) on board the observatory exhausted its supply of liquid helium rendering the HFI unusable. The final deactivation command, which switched off the spacecraft's transmitter, was sent to Planck on the 23rd October 2013.


25th October 1789

Samuel Heinrich Schwabe. German astronomer remembered for his work on sunspots. Schwabe was looking for a possible planet inside the orbit of Mercury.

Because the proximity to the Sun would make it difficult to observe such a body Schwabe believed one possible way to detect a new planet would be to see it as a dark spot when passing in front of the Sun.

From 1826 to 1843 he observed the Sun and recorded its spots trying to detect any new planet among them. He did not find one but noticed the regular variation in the number of sunspots and published his findings in a short article entitled "Solar Observations during 1843". In it he made the suggestion of a probable cycle of approximately eleven years. The periodicity of sunspots is now fully recognized. Schwabe thus made one of the most important discoveries in astronomy. In 1857 Schwabe was awarded the Gold Medal of the Royal Astronomical Society. The image right is by Monty Leventhal OAM, who is a regular solar observer and Sydney City Skywatchers and BAA member. You can read his observations and find out more about the solar cycle here. Also see an example of the regularity of the solar cycle in this blog post.

20th October 1891

(Sir) James Chadwick. English physicist. Best known for his discovery in 1932 of the neutron, a particle with no electric charge that, along with positively charged protons, make up an atom's nucleus. This prepared the way towards the fission of Uranium 235 and the creation of the atomic bomb. For this discovery he was awarded the Hughes Medal of the Royal Society in 1932, and subsequently the Nobel Prize for Physics in 1935. He was knighted in Britain in 1945 for his achievements in physics. A crater on the Moon, Chadwick, is named after him.

11th October 1969

Merieme Chadid. Moroccan-French astronomer and astrophysicist who leads international polar scientific programs and has been committed to installing a major astronomical observatory in Antarctica.

She became the first Moroccan as well as the first female French astronomer to reach the heart of Antarctica in 2005 when she achieved her first polar expedition to set up a new observatory.

Chadid promotes scientific education by giving lectures and supervising students. Her documentary on astronomy, Tarik Annujah, has played on the Al Jazeera Children's Channel. Her research aims to explain and decipher early star formation and stellar evolution and pulsation towards the understanding of the Universe.

In 2015 she was awarded the Arab Woman of the Year Award for Achievement in Science by Regent's University London. Image above courtesy of Merieme Chadid.


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