In this month: July 2022

1st July 2013

Hippocamp, a moon of Neptune, is discovered. With a diameter of approximately 35 kilometres it is the smallest moon that orbits Neptune, far too small to have an atmosphere like other larger moons. Due to its small size it was completely missed by the Voyager 2 spacecraft when it was exploring the planet and its moons and wasn’t discovered until 2013 from images taken from the Hubble Space Telescope years earlier. The diagram below is courtesy NASA.

It took until 2019 for it to be named an official moon of Neptune. The tiny moon orbits Neptune at a distance of 105,283 kilometres and takes around 23 hours to orbit the planet going at speeds of 32,000 kilometres per hour.

Hippocamp takes its name from the Greek mythological creature Hippocampus, a half horse, half fish hybrid that roams the ocean.

23rd July 1999

Eileen Collins becomes the first woman to command a space shuttle mission with the launch, from Cape Canaveral, Florida, of the Space Shuttle, Columbia. Under her leadership the Chandra X-ray telescope was deployed into orbit. The image below of Eileen Collins is courtesy NASA.

The telescope went on to make many significant astronomical discoveries by observing the cosmos in X-ray light. It is still operating today. The mission duration was 4 days, 22 hours, 49 minutes, 37 seconds. The payload was also the heaviest payload ever carried by the Space Shuttle system at over 22.7 tonnes.

It was Eileen Collins third shuttle flight. She logged 38 days and 10 hours of space flight time during her career as an astronaut. Eileen Collins retired from NASA in 2006.

She is one of only two female Space Shuttle Commanders. In 2007, eight years after Collins flight, Pamela Melroy commanded the STS-120 mission of the Space Shuttle Discovery.

31st July 1999

NASA’s Lunar Prospector is deliberately crashed into a permanently shadowed area of the Shoemaker crater near the south pole of the Moon to see if there is water frozen inside the deep polar crater. Scientists had hoped to detect a cloud of water vapour in the lunar sky resulting from the 6,115 kilometre per hour impact, however no clear evidence of a plume was observed or photographed.

Artwork right courtesy NASA.

Among its other duties the Lunar Prospector carried the ashes of the deceased astronomer and geologist, Gene Shoemaker who was killed in a car accident in Australia’s Northern Territory in July 1997. His ashes were carried to the Moon as a tribute to a scientist who narrowly missed out on being selected for the Apollo program of manned landings. Shoemaker is the first person to be buried on another celestial body.


21st July 1620 Jean Picard.

Not to be confused with the fictional Jean-Luc Picard from the Star Trek television series, Jean Picard was a French astronomer and Jesuit priest. He was the first person to measure the size of the Earth to a reasonable degree of accuracy by measuring one degree of latitude along the Paris Meridian getting a radius of 6,328.9 kilometres, an error of only 0.44% less than the accepted value today. Isaac Newton was to use this value in his Theory of Universal Gravitation. The current polar radius has now been measured at just over 6,357 kilometres. Picard is also credited with the introduction of telescopic sights and the use of pendulum clocks as contributions to greater precision in astronomical observations. He also developed what became the standard method for measuring the right ascension of a celestial object. During his career Picard collaborated with many scientists, including Isaac Newton, Christiaan Huygens, and his main rival Giovanni Cassini, although Cassini was often less than willing to return the gesture. The lunar crater Picard on the southwest quadrant of Mare Crisium, is named in his honour. The PICARD mission (2010-2014), an orbiting solar observatory, was named after him.

7th July 1816 Johann Rudolf Wolf.

Swiss astronomer.

Best known for his research on sunspots. He was greatly impressed with the discovery of the sunspot cycle by German astronomer Heinrich Schwabe. Wolf carried out his own observations and collected all available data on sunspot activity from as far back as 1610. He calculated a period of 11.1 years for the cycle. In 1848 he devised a way of quantifying sunspot activity.

The Wolf Number, as it is now called, still remains in use. In 1852 Wolf was one of four people who discovered the link between the cycle and geomagnetic activity on Earth.

20th July 1890 Julie Marie Vinter Hansen

Danish astronomer.

While studying at the University of Copenhagen she was appointed a computer at the University's observatory in 1915 (In the pre-electronic era, “computers” were humans that did hand calculations at the direction of astronomers).

She was the first woman to hold an appointment at the University. She was later appointed Observatory Assistant and, in 1922, Observer. By 1939, Hansen was promoted to the First Astronomer at the Observatory and widely known for her accurate computations of orbits of minor planets and comets. She later became Director of the International Astronomical Union's Telegram Bureau and Editor of its Circulars. The minor planet 1544 Vinterhansenia, discovered by Finnish astronomer Liisi Oterma is named in her honour.

Image left: Courtesy University of Chicago archives