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In this month: September

9th September 1892

Amalthea, a moon of Jupiter, is discovered by Edward Emerson Barnard using the 36 inch (91 cm) refractor telescope at Lick Observatory. It was the last natural satellite in the solar system to be discovered by direct visual observation, all later moons were discovered by photographic or digital imaging. It was also the first new satellite of Jupiter to be discovered since Galileo’s discovery of the Galilean moons in 1610.

Amalthea is irregularly shaped with a very red surface and heavily scarred by craters. It orbits Jupiter at a distance of 181,400 kilometres. The images above were taken by NASA's Galilean Spacecraft.and they show Amalthea and other moons of Jupiter and are Courtesy NASA/JPL/Cornell University.

The moon is named after the nymph Amalthea from Greek mythology, who nursed the infant Zeus (the Greek equivalent of Jupiter). The name "Amalthea" was initially suggested by Camille Flammarion but was not formally adopted by the IAU until 1976. Before that Amalthea was most commonly known as Jupiter V.

12th September 1959: LUNAR 2

The Soviet spacecraft Luna 2 is launched becoming the first successful attempt for any nation to reach the surface of the Moon, and the first human-made object to make contact with another celestial body. Following a direct path to the Moon it impacted the Moon's surface at about 3.3 kilometres per second, east of Mare Imbrium near the craters Aristides, Archimedes, and Autolycus. The spacecraft’s magnetometer measured no significant lunar magnetic field, and the radiation detectors found no evidence of a radiation belt.

On the 1st November 1959, the Soviet Union released two stamps depicting the trajectory of the spacecraft to commemorate the mission.

15th September 2017

The spacecraft Cassini is deliberately crashed into Saturn. After 20 years in space, 13 of those years exploring Saturn, Cassini exhausted its fuel supply. To protect the moons of Saturn that could have conditions suitable for life, Cassini was sent on its "grand finale" executing a number of risky passes through the gaps between Saturn's inner rings The atmospheric entry of Cassini ended the mission, but analysis of the returned data will continue for many years.

The mission was a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study Saturn and its system, including ts rings and natural satellites.


16th September 1846

Seth Carlo Chandler Jr. American astronomer.

He is best remembered for his research on polar motion and for what is known today as the Chandler wobble (the change in the spin of Earth on its axis. An analogy is the wobble in a toy top when it first starts spinning or slows down. Its "poles" do not spin in a perfectly straight line). Chandler also made contributions to other areas of astronomy, including variable stars and computing the orbital parameters of asteroids and comets. He independently co-discovered the nova, T Coronae Borealis.

Chandler was awarded the Gold Medal of the Royal Astronomical Society in 1896.

The lunar crater Chandler is named after him.

The Image above shows the wobble prior to 2000, Credits: NASA/JPL-Caltech

13th September 1912

Horace Welcome Babcock. American astronomer.

He was the son of astronomer Harold D. Babcock. In 1953 Horace was the first to propose the idea of adaptive optics, a technology used to improve the performance of telescopes by reducing the effect of incoming distortions. Babcock also specialized in spectroscopy and the study of magnetic fields of stars. He proposed the Babcock Model, a theory for the magnetism of sunspots. During his time as Director at Mt Wilson and Palomar Observatories he was instrumental in the creation of the Las Campanas Observatory in Chile. His establishment of the Las Campanas Observatory, with its exceptional location, infrastructure, and telescopes is considered to be his main legacy to astronomers today. The Asteroid 3167 Babcock is named, jointly with his father, in their honour.

Left: Horace W. Babcock addressing guests at the dedication of the 60-inch telescope, Palomar Observatory in October 1970. Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California.

4th September 1929

Elizabeth Pat Roemer American astronomer.

She was noted as a recoverer of lost comets being credited with the recovery of 79 comets during her career. She took an extensive set of photographic plates of comets over 25 years to obtain data for the magnitudes of comet nuclei. In 1972 she successfully imaged Comet Encke just 10 days from aphelion and also observed 65P/Gunn close to aphelion. She discovered two main-belt asteroids 1930 Lucifer and 1983 Bok. In 1975 she also co-discovered Themisto, one of the moons of Jupiter.

Roemer won many awards and was a leader in several professional astronomy organizations

The inner main-belt asteroid 1657 Roemera, discovered by Swiss astronomer Paul Wild in 1961, was named in her honour.

Image of Pat Roemer taken in 1963, Courtesy: Acc. 90-105 - Science Service, Records, 1920s-1970s, Smithsonian Institution Archives