top of page

Astronomical anniversaries in the month of May

15th May 1618

Johannes Kepler discovers the mathematical rule governing the orbits of our solar system’s planets. The image left is form a painting by an unknown artist in 1610.

Known as Kepler’s Third Law of Planetary Motion it states …. “The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit” …. or to put it more simply, if you square the 'year' of each planet and divide it by the cube of its distance to the Sun, you get the same number, for all planets.

His first two laws of planetary motion were published in the year 1609. Together, the three laws modified the heliocentric theory of Nicolaus Copernicus, replacing its circular orbits and epicycles with elliptical trajectories.

3rd May 1661

The first transit of Mercury is observed from England. This was also the coronation day of King Charles II. Among the observers to observe the transit from London were Edmond Halley and Dutch astronomer Christiaan Huygens who was in London at the time. Huygens realised that transit observations would be instrumental in measuring the distance between the Earth and the Sun.

15 May 2005

Nix and Hydra, two moons of Pluto, are discovered. The moons were imaged by astronomers of the Pluto Companion Search Team using the Hubble Space Telescope while preparing for the New Horizons mission. Nix and Hydra are roughly 5,000 times fainter than Pluto and about two to three times farther from Pluto than its large moon, Charon. Both moons are approximately 50 kilometres wide.

Nix (or Nyx) is named for the Greek goddess of darkness and night. She is known to have been born from chaos. The image left is from a ceramic painted by Brygos an ancient Greek potter 4th Century BC.

Hydra is named after the nine-headed underworld serpent in Greek mythology.


20th May 1941 Betty Louise Webster.

Australian astronomer and physicist. In 1971, with her colleague, Paul Murdin, she identified the powerful X-ray source Cygnus X-1 as the first clear candidate for a black hole. She was the driving force for the Automated Patrol Telescope at the Siding Spring Observatory, served on and chaired many committees and promoted astronomy very actively through the International Astronomical Union and

the Astronomical Society of AustraliaShe died at the relatively young age of 49.

The Louise Webster Prize has been awarded annually since 2009 by the Astronomical Society of Australia to reward outstanding postdoctoral research early in a scientist's career.

26th May 1826 Richard Christopher Carrington.

Richard Christopher Carrington's (1826–1875), house and Observatory, Furze Hill, Redhill, Surrey, UK.

English amateur astronomer. On the 1st September 1859, Carrington and Richard Hodgson, another English amateur astronomer, independently made the first observations of a solar flare during a geomagnetic storm. This geomagnetic storm of 1859 is often called the Carrington event.

Carrington also determined elements of the rotation axis of the Sun, based on sunspot motions, and his results remain in use today and won the Gold Medal of the Royal Astronomical Society in 1859.

28th May 1788 Carl Ludwig Christian Rümker.

German astronomer. In 1821 Rümker arrived in New South Wales as astronomer at the Parramatta observatory built by Sir Thomas Brisbane. After Brisbane's departure from NSW in 1825 Rümker was placed in charge of the observatory.

On the 2nd June 1822 Rumker rediscovered Encke's comet. For this achievement he was awarded a silver medal and £100 by the Royal Astronomical Society, a gold medal by the Institut de France, and was granted a land grant of 405 hectares at Picton. After a quarrel with the President of the Royal Astronomical Society, Rumker was dismissed from government service and left NSW never to return to Australia. He took charge of the new Hamburg Observatory where his chief work was concerned with cataloguing stars. A catalogue of the stars of the Southern Hemisphere was published in 1832 in Hamburg. The lunar mountain Mons Rümker, image below courtesy NASA, is named for him.


bottom of page