An astronaut's view

"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.