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Astronomical happenings in October

24th October 1851

William Lassell finds not one, but two moons of Uranus on the same night when he discovers Umbriel and Ariel. There is little information on both moons as they have only been visited once in 1986 by the Voyager 2 spacecraft.

Ariel is the second closest moon to the planet at a distance of 190,000 kilometres, and takes about 40 hours to complete an orbit. It is the fourth largest out of all the 27 known moons of Uranus with a diameter of 1,158 kilometres and is the most reflective. Image left: The complex terrain of Ariel is viewed in this image, the best Voyager 2 color picture of the Uranian moon. Image Credit:NASA/JPL

Umbriel is the darkest of Uranus' largest moons, reflecting only 16 percent of the light that strikes its surface. It orbits Uranus at a distance of about 266,000 kilometres, the third farthest among the five major moons. It takes about four 4 days to complete one full orbit around Uranus. Both moons take their name from Alexander Pope’s poem The Rape of the Lock. Ariel is also mentioned in William Shakespeare’s The Tempest.

Image right: Umbriel by NASA / Jet Propulsion Lab -

11th October 1984

Kathryn Sullivan becomes the first American woman to perform a spacewalk on the STS 41-G mission when she leaves the Challenger space shuttle for 3.5 hours with crewmate David Leestma to demonstrate the feasibility of refuelling satellites in orbit, a key task for satellite servicing.

They had trained for this task in the underwater neutral buoyancy simulators at NASA’s Marshall and Johnson Centres. She was the first woman to wear the 225-pound Extravehicular Mobility Unit (EMU) to work in space. It was a ready-to-wear suit, not custom-made, with interchangeable arms, legs, and torso units in different sizes.

Sullivan flew twice more in space on the Discovery and Atlantis space shuttles but did not go on other spacewalks. After 532 hours in space and an illustrious career on earth, she retired from NASA in 1993.

She is an advocate for women in STEM and has spoken about having a lack of female role models in the fields that she was interested in while growing up. She has spoken many times about her hope for improved diversity and female representation in the scientific, technological, engineering and mathematical (STEM) fields. Image above: NASA.

19th October 2017

Oumuamua, the first interstellar object to pass through the solar system, is discovered using the Pan-STARRS telescope at the Haleakalā Observatory, Hawaii, When it was first observed it was about 33 million kilometres from Earth travelling at a speed of 87 kilometres per second—too fast to have originated in the Solar System - and already heading away from the Sun. It is the first known interstellar object to visit our solar system. It is a small object estimated to be between 100 and 1,000 metres long, with a width and thickness both estimated between 35 and 167 metres and is red in colour.

Despite its close approach to the Sun, it showed no signs of having a coma.

Astronomers officially named the object 1I/2017 U1.

The name Oumuamua, chosen by the Pan-STARRS team, is Hawaiian in origin and roughly translates to 'first distant messenger'.

Image left: Artist's concept of interstellar object1I/2017 U1 ('Oumuamua), European Southern Observatory / M. Kornmesser


23rd October 1894, Emma Vyssotsky (née Williams). American astronomer.

In 1927 she enrolled in astronomy at Radcliffe College now part of Harvard where she worked with Cecilia Payne on the "spectral line contours of hydrogen and ionized calcium throughout the spectral sequence”. In 1930 she received her PhD in astronomy from Harvard College for her dissertation titled, A Spectrophotometric Study of A Stars. At the time, she was only the third individual to be awarded a PhD in astronomy from Harvard.

She followed her husband, astronomer Alexander Vyssotsky, to the University of Virginia where she spent her astronomy career at the McCormick Observatory at the university. Her specialty was the motion of stars of the Milky Way.

In 1946, she was awarded the Annie J. Cannon Award in Astronomy by the American Astronomical Society in recognition of her contributions to the field of stellar spectra.

6th October 1931 Riccardo Giacconi. Italian-American astrophysicist.

He paved the foundations of X-ray astronomy and worked on instrumentation from rocket-borne detectors in the 1950s and 1960s, to Uhuru, the first orbiting X-ray astronomy satellite, in the 1970s and onto the Einstein Observatory, and the Chandra X-ray Observatory. He also applied his expertise to other fields of astronomy, becoming the first permanent director of the Space Telescope Science Institute, followed by Director General of the European Southern Observatory (ESO).

In 2002 he was awarded a share of the Nobel Prize in Physics "for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources". The other shares of the Prize in that year were awarded to Masatoshi Koshiba and Raymond Davis, Jr. for neutrino astronomy.

Asteroid 3371 Giacconi is named in his honour. Image above::ESO/C. Madsen

17th October 1956 Mae Carol Jemison. American engineer, physician, and former NASA astronaut.

She became the first African-American woman to travel into space when she served as a mission specialist onboard the Space Shuttle Endeavour in 1992. She logged 190 hours, 30 minutes, 23 seconds in space and orbited the earth 127 times. It was her only space mission.

Jemison left NASA in 1993. She holds several honorary doctorates and has been inducted into the National Women's Hall of Fame and the International Space Hall of Fame. Jemison continues to advocate strongly in favour of science education and getting minority students interested in science. She is a member of various scientific organizations, such as the Association of Space Explorers and the American Association for the Advancement of Science.

In 2019 the Google Doodle for International Women's Day featured a quote from Jemison: "Never be limited by other people's limited imaginations."

Image above: Mission Specialist Mae Jemison poses in Spacelab-Japan, 1992. (National Archives Identifier 22725970)


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