ESA astronaut Paolo Nespoli works on the wind station in the Sa Grutta cave's so-called "4th Wind" narrow massage. Paolo joined a group of six international astronauts on ESA's CAVES 2013 campaign in Sardinia, Italy. During CAVES, an abbreviation for Cooperative Adventure for Valuing and Exercising human behaviour and performance Skills, six astronauts spend two weeks deep in caves, in the dark and cold. They are separated from the outside world, doing scientific research and daily tasks together, as a group, just like in space. Moving in the cave system is also comparable to spacewalking with the use of harnesses and safety devices.

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More about CAVES 2013: http://www.esa.int/Our_Activities/Human_Spaceflight/Caves/Join_the_underground_adventure

In this Hubble Space Telescope composite image taken in April 2013, the sun-approaching Comet ISON floats against a seemingly infinite backdrop of numerous galaxies and a handful of foreground stars. The icy visitor, with its long gossamer tail, appears to be swimming like a tadpole through a deep pond of celestial wonders.

In this composite image, background stars and galaxies were separately photographed in red and yellow-green light. Because the comet moved between exposures relative to the background objects, its appearance was blurred. The blurred comet photo was replaced with a single, black-and-white exposure.

The images were taken with the Wide Field Camera 3 on April 30, 2013.

This photo is one of the original images featured on ISONblog, a new online source offering analysis of Comet ISON by Hubble Space Telescope astronomers and staff at the Space Telescope Science Institute in Baltimore, USA.

A pair of 3D-printed replicas of the glove worn by ESA astronaut Hans Schlegel while spacewalking, one lifesize and one at one-tenth scale. These models were produced using fused deposition modelling of thermoplastic by ESA's Mechanical Workshop based at ESTEC in Noordwijk the Netherlands. 

This image was taken over central Athens, the capital and largest city of Greece.

Known as the birthplace of democracy, it is one of the oldest cities in the world. During the classical period of Ancient Greece, this was the centre for arts, philosophy and learning, home to many politicians, writers and philosophers.

Near the centre of the image is the famous Acropolis of Athens – standing high about the surrounding city as evident by the shadow to the north. Several ancient structures, including the Parthenon, illustrate the civilisations of Greece over more than a millennium.

Nearby to the southeast is the Temple of Zeus, with shadows from the remaining standing columns stretching across the grass. Further northeast are the National Gardens surrounding the Zappeion building. At the upper left corner of the gardens is the Greek parliament building overlooking Syntagma Square.

In the lower-right corner we can see the large, white marble Panathenaic Stadium. Originally built for the athletics part of the Panathenaic Games – in honour of the goddess Athena – it has been rebuilt, enlarged, excavated and refurbished over the centuries. In 1896 it hosted the first modern Olympic Games, which saw over 240 athletes from 14 nations.

This image, also featured on the Earth from Space video programme, was acquired on 4 January 2013 by DigitalGlobe’s WorldView-2 commercial satellite.

Mission logo for ESA astronaut Alexander Gerst's mission to the International Space Station set for 2014: Blue Dot.

This animation represents the evolutionary process of a pulsar as it swings between X-ray and radio emission. The pulsar (left) is in a binary system with a low-mass star as a companion (right). The two objects orbit around their mutual centre of gravity; for clarity, this motion is not shown in the animation.

At the beginning of the animation, the pulsar spins very fast emitting two narrow beams of radio waves (shown in purple). Over several million years this rotation gradually slows down. Eventually, the gravitational pull of the pulsar starts drawing matter from the companion star. As the pulsar accretes matter via an accretion disc, it gains angular momentum and its rotation becomes extremely rapid again.

During the accretion process, the high density of accreted matter damps out the radio emission and is seen only in X-rays (shown as wide, white beams). When the accretion rate decreases, the pulsar’s magnetosphere expands and pushes matter away. As a consequence, the X-ray emission becomes weaker, while the radio emission intensifies.

The pulsar swings back and forth between the two states several times over several hundreds of millions of years until it final slows down to become a purely radio-emitting pulsar, while its companion star has evolved into a white dwarf.

Read more: Missing link found between X-ray and radio pulsars