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  • Elizabeth Cocking and Toner Stevenson

Astronomical happenings in December


23 December 1672 Italian astronomer Giovanni Domenico Cassini observes Rhea, one of Saturn's Moons.

Cassini discovered four of Saturn's Moons and he named three of them after Greek mythological figures, Rhea is named after the Ancient Greek mother goddess, daughter of Gaia and Uranus. The image above is a glass Saturn Christmas tree ornament, of no astronomical significance, photo: T. Stevenson, 2021.

There was much speculation about what Rhea was made of and indeed if it had rings. The first images of Rhea were taken by Voyager 1 and Voyager II. It was not until NASA sent up the Cassini-Huygens mission to make five fly-bys that closer observation and correlation revealed that there were no rings, that the surface is full of craters and that the entire planet is three quarters ice, and one quarter rock. You can find out more here.

The image left is a false colour photograph taken by NASA's Cassini orbitor in December 2010, credit: NASA,JPL,SSI.

21st December 1968 Launch of Apollo 8 the first mission to take humans to the Moon and back.

It was the first crewed spacecraft to leave low Earth orbit, and also the first human spaceflight to reach another astronomical object - the Moon - which the crew orbited without landing. The three astronauts, Frank Borman, James Lovell, and William Anders, were the first humans to witness and photograph an Earthrise. They orbited the Moon ten times over the course of twenty hours, during which they made a television broadcast on Christmas Eve where they read the first ten verses from the Book of Genesis.

The historic mission happened because of a last-minute call by NASA. At the time the United States and Russia were engaged in a "space race" and NASA, being mindful of crew safety, wanted to bring Americans to the moon as soon as possible. Sending Apollo 8 into lunar orbit after only one previous Apollo mission, which had remained in Earth orbit, was a bold decision.

3rd December 1973 The first flyby of Jupiter by the Pioneer 10 spacecraft.

After becoming the first spacecraft to pass through the asteroid belt, it passed by the planet at a distance of 130,000 kilometres above the cloud tops. The rendezvous provided the first close-up images of the planet and data on the planet’s magnetic field which proved Jupiter to be a primarily liquid planet. After Pioneer 10 flew by Jupiter it began its journey into interstellar space heading towards the star Aldebaran which it will encounter in 2 million years. Pioneer 10 carries a plaque with a message to any intelligent life it might meet on its journey. The plaque includes diagrams of Earth's location and drawings of a man and a woman.

After operating for more than 30 years, the successful Pioneer 10 spacecraft sent its last, very weak, signal to Earth on the 23rd January 2003.


28th December 1944

Sandra Moore Faber. American astrophysicist .

Professor Faber is known for her research on the evolution of galaxies. She is the University Professor of Astronomy and Astrophysics at the University of California and works at the Lick Observatory, California.

She has made discoveries linking the brightness of galaxies to the speed of stars within them and was the co-discoverer of the Faber–Jackson relation (one of its main uses is as a tool for determining distances to external galaxies.) She was also instrumental in designing the Keck telescopes in Hawaii.

The minor planet #283277 Faber is named for her.

Photograph courtesy University College Santa Cruz.


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