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On this day in 2005 - January 5th - dwarf planet Eris was discovered by Mike Brown and Chad Trujillo.

There was no category of dwarf planet then, and since the new object seemed to be bigger than Pluto, the discoverers assumed it was a new planet. But the following year it was bad luck for Pluto and Eris. Click to find out more about Eris - Dwarf Planet.

On this day in 1610 - January 7th - Galileo discovered three of Jupiter's moons: Io, Europa and Callisto.

It was astonishing to find that Jupiter had three satellites. Actually, there are many more, but these are large enough to be visible in a small telescope. In those days, the Earth was generally considered to be the center of the Universe with everything revolving around it. This discovery showed that not everything went around the Earth. Click to find out more about Jupiter's Galilean Moons.

On this day in 1942 - January 8th - Stephen Hawking was born.

One of the greatest theoretical physicists and cosmologists of our time, he became Lucasian Professor of Mathematics at Cambridge in 1979, holding the same chair as Sir Isaac Newton had done in 1669. Overcoming severe disability, Professor Hawking has made ground-breaking contributions to the study of the Universe. Here's Stephen Hawking's website if you want to find out more about him.

On this day in 1787 - January 11th - William Herschel discovered two moons of Uranus.

Herschel had discovered the planet Uranus in 1781, the first planet ever to be discovered - the others had been known since antiquity. We now know of 27 moons in the Uranian system, and Herschel discovered the first two: Titania and Oberon, though he didn't name them.

Over seventy years later William Lassell discovered two more moons of Uranus, and asked John Herschel, William's son, for suggestions for naming the four known moons. Herschel opted for literature rather than mythology and subsequent moons have also been named from Shakespeare.

You can find out more about the Literary Moons of Uranus.

On this day in 1916 - January 14th - the first women were admitted as full members of the Royal Astronomical Society.

Mary Adele Blagg, Ella K Church, A Grace Cook and Fiammetta Wilson became the first elected female Fellows of the RAS on 14 January 1916. Six more followed that year, including Annie Maunder, more than 24 years after her first attempt to join.

The society was formed on January 12, 1820 as the Astronomical Society of London becoming the Royal Astronomical Society after receiving a royal charter from William IV.

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On this day in 2015 - January 16th - ESA announced that Beagle 2 had been found in Mars Reconnaissance Orbiter images, finally solving a 12-year-old mystery.

In 2003 UK-led Beagle 2 lander, having hitched a ride on the European Space Agency's Mars Express, had been released into Martian orbit and was scheduled to land on Christmas Day. No contact was ever made. You can read the unusual story of Beagle 2 - Lost and Found.

On this day in 1747 - January 19th - Johann Bode was born.

Bode was one of the most important astronomers of his time. He was the author of two important star atlases, director of the Berlin Observatory for forty years and compiled tables of astronomical data. His name is still associated with a relationship called Bode's Law.

On this day in 1573 - January 20th - Simon Marius was born.

Marius was a German astronomer who claimed to have discovered the moons of Jupiter before Galileo. Although this couldn't be substantiated, he did give the moons their names.

On this day in 2003 - January 22nd - Pioneer 10's last signal was received.

Pioneer 10 was launched on March 3, 1972 and is now the second most distant probe from Earth at over 114 AU. (1 AU is the average Earth-Sun distance.) It's headed in the direction of the constellation Taurus. The most distant probe is Voyager 1, currently at over 134 AU.