Smiling for the camera: Together with his colleagues Reid Wiseman and Maxim Surajew, Gerst flew back to earth in a Russian Soyuz craft. After three-and-a-half hours, they landed in the middle of the Kazakh steppe, at the Baikonur Cosmodrome. The mission started from the same space launch complex at the end of May this year.

The 166 days in Gerst spent in space have left their mark: Gerst's muscles have been weakened, and it will take some time for his sense of orientation to return. Helpers had to carry him away after the landing. "Thank you for your support, everybody," were Gerst's first words back on planet Earth.

Pizza, beer and the spring landscape are some of the things Alexander Gerst will be looking forward to experiencing. His terse summary of the time in space: "The hard work was really worth it." During the last press conference held while he was still at the ISS, he said he'd never really felt lonely - the crew was "like a family."

There was only a thin spacesuit between Gerst and the vacuum of space on October 7, when he did his first spacewalk. Gerst and his colleague were able to quickly modify a robotic arm, and had plenty of time to take stunning shots of Earth. A geophysicist, Gerst is familiar with natural phenomena such as this low-pressure system above the northern Atlantic Ocean.

We don't know a lot about how things we know on Earth behave in space. Alexander Gerst did his part to change that as part of the Blue Dot mission - he was tasked with conducting 100 experiments during his mission. This included work with a electromagnetic levitator, a furnace that can melt and solidify metals with a twist of a crank.

All astronauts have a daily sports routine - leg and gluteal muscles otherwise diminish quickly in weightlessness. These activities, combined with medical experiments, will help scientists on earth learn more about the human body.

During his stay on the ISS, Alexander Gerst had to regularly take his own blood samples, to both monitor his health, and study how weightlessness affects the human organism. These sample results were then sent to earth and examined by scientists in a lab. Gerst jokingly called his regular bleedings "my sacrifice for science."

Though there was much to do on the ISS, Alexander Gerst still found time to watch the World Cup final via satellite. He even brought the 2014 jersey to space and celebrated Germany's fourth victory. This picture was shown all over the globe after he uploaded it on Facebook and Twitter.

In taking photos of planet Earth from space, Gerst sought to emphasize the beauty and individuality of our planet - a small blue dot in space. The ISS crew placed emphasis on educational work, to try and raise awareness about the problems and threats facing our planet. Alexander Gerst communicated with the public on a near-daily basis via social media.

The German astronaut also found time for interviews with people from all over the planet. He fielded questions from schoolchildren, and posted many videos and pictures showing his work on the ISS. Gerst also maintained a blog sharing what experiments he was currently undertaking.

"Hello Berlin, I don't see any borders from up here!" Gerst tweeted on November 9th 2014, the 25th anniversary of the fall of the Berlin Wall. Apart from conducting a number of experiments in various scientific disciplines, Alexander Gerst had another important mission: to show people on Earth how beautiful and fascinating our "Blue Dot" is.

"Words can't describe how it feels flying through an Aurora" - that's how Alexander Gerst described his experience with this natural phenomenon. Although he found it difficult to capture the experience in words, he was able to conduct research into auroras. One aim was to investigate the influence of our planet's electromagnetic forces on electronic devices at the International Space Station.

Even on Earth, one rarely gets to see the Aurora Borealis, or Northern Lights. Alexander Gerst was fortunate to get this great shot from space of the Northern Lights in the polar region.

It is neither a mountain, nor a vulcano. In fact, this picture taken by Alexander Gerst shows Barringer Meteorite Crater in Arizona. Gerst would often share his photos on social media with the hashtag #geochallenge, challenging the public to try and figure out where the geographical feature might be.

It looks like a tiny hole, but actually measures 80 kilometers (50 miles) wide. Despite its interesting appearance, typhoons like this one can cause tremendous damage on the Earth's surface. "From up here it is surprisingly obvious that our world is one connected system," Gerst observed from space.

On thing that makes Alexander Gerst's photos so beautiful and fascinating is how they are unstaged, authentic snapshots. In this image, which Gerst tweeted as the saddest photo he's taken yet, explosions and rockets are visible in Gaza and Israel.

Gerst's images, including this one of windswept valleys in North Africa, can be compared to previous, similar images. This helps scientists observe changes on the Earth's surface and determine whether they are natural or manmade.

The circles on this image are not the work of aliens, but rather irrigated agricultural fields in arid regions of Mexico. Some of Gerst's experiments dealt with food - for example, the astronauts grew edible plants on the space station to see if they could develop methods to use water more efficiently.

Some images Gerst took look like the works of a talented painter. This image shows a river in Kazakhstan snaking its way through the landscape. Defunct bends of the river are also visible, and one can imagine how it's likely to change course again in the future.

"When light from the Cupola tints ISS orange inside, I can tell we're over Africa without even looking out the window," Gerst had tweeted. The Sahara Desert is perceived to be endless - when one is in it. But as this image of Libya shows, even the sand dunes there have a beginning and an end.

On Wednesday, September 9, Cologne's Envihab kicks off a study in which 12 test subjects will feel what it's like to be in space. The catch? They'll have to lie down for two months straight. DW takes a look.

Astronauts' bodies undergo stress when they travel to and through space - their metabolic and endoctrine systems, among others, change. The Envihab research lab in Cologne aims to understand how the body evolves in space.

When astronauts return to Earth from the International Space Station (ISS) they cannot walk. Their muscles have degenerated during the period of weightlessness. Without gravitation, blood moves away from the legs and builds up in the head.

This fitness machine is attached to a short-arm centrifuge. Astronauts can use it to exercise their muscles. This kind of centrifuge can be to simulate gravity used during long space missions.

The centrifuge at Envihab can go up to six times the Earth's gravitational acceleration - like during a rocket launch or in a fighter jet. This ultrasound machine, attached to a robot arm, can examine how the heart reacts during this process.

The doctor can move the ultrasound machine very close above the test subject's body, allowing him to look directly into the heart or at other organs to see if they have moved during the intense accelerations, and whether or not blood vessels swell or decrease in size.

EEGs, like the one shown here, help sleep researchers better understand how brain waves change , for instance when people nod off.

On Earth, it's pretty simple - gravitation always pulls us down. The universe around us seems to stand still. But in space, there's no up and down. So astronauts practice tricky maneuvers, like docking a space capsule, on computers before taking off.