London is known for overcast skies and light pollution. Nonetheless for five months of the year there is one place where the night sky can be seen in its glory: Greenwich, at the Astronomy Photographer of the Year exhibition. And if you can't go in person, you can go online to gasp at the glow of the Galaxy, be awed by aurorae, marvel at meteors and be dazzled by deep space.

This is the fifth year of the competition and there were over 1200 entries. The four main categories are Earth and Space, Our Solar System, Deep Space, and the Young Astronomy Photographer. There are also three special prizes: People and Space, Robotic Scope and the Sir Patrick Moore Prize for Best Newcomer. The final award was renamed this year in honor of the well-known English broadcaster and astronomy popularizer who died in December 2012.

Modern cameras can produce excellent results at a reasonable price. But to get an outstanding picture, you need a good eye. You also need to be able to process the images to realize your picture. In sports like figure skating, judging is on technical merit and on artistic interpretation. In a way, this also applies to photography. A technically-adept photo which is rather commonplace won't be able to compete with an interesting one.

The winner
Try to imagine a beautiful cape on the coast of New Zealand's North Island. There's a lighthouse in the distance. The sky is so dark, and the night so clear, that the Milky Way arches across a star-filled sky. If you live in a city, as I do, it may be difficult to imagine being in such a place. But this is where Australian photographer Mark Gee took the photo that wowed the judges, won the Earth and Space prize, and became the overall competition winner.

“Guiding Light to the Stars” is a panorama made up of twenty images stitched together. If you look to the left of the arch, you can see the nebulous figures of two companion galaxies of the Milky Way, the Large and Small Magellanic Clouds. They are common sights in the southern hemisphere, but in the northern hemisphere are visible only below latitudes of about 20 degrees north. The way the lighthouse is lined up with one end of the arch of the Milky Way really seems to connect the Earth with space.

Mark Gee also won the prize in the People and Space special category. By photographing the rising Moon from over 2 km away, an enormous Moon dwarfed the silhouetted people who have gathered to see it. There is a perceptual illusion that makes the Moon seem larger when it's near the horizon. But for it to look extremely large, the photographer has to be at a distance from the foreground objects.

Our Solar System
There were three superb pictures of the Sun among the five prize winners in Our Solar System. But what really caught my eye was “Cosmic Alignment” by Ignacio Diaz Bobillo. The Argentinian photographer managed to get three celestial objects in the same frame: Comet Lemmon, 47 Tucanae, and the Small Magellanic Cloud.

Strictly speaking, only the comet – unless you count the photographer – is in the Solar System. The Small Magellanic Cloud, a galaxy which also appears in Mark Gee's skyscape, is over 200,000 light years away. And in our Galaxy, but around 16,700 light years away, is the globular cluster 47 Tucanae. A globular cluster is a cluster of stars that is so dense that their mutual gravity pulls them into a spherical shape. These three objects represent three different distance scales. (Diaz Bobillo was also highly commended in the Deep Space category for an image of star cluster Omega Centauri.)

Deep Space
The Deep Space images, like their professional equivalents, often have an abstract artistic appearance. “Celestial Impasto” by Adam Block, the winner in this category, is an excellent example. Nebula Sh2-239 is a star-forming region. Dust is typical of such a region, for the developing stars are shrouded in it. As the stars heat up, their radiation energizes hydrogen gas, which shows up as a red nebula. The dustiness gives this image a feeling of the depth, motion and texture of a painting.

Young Astronomy Photographer of the Year
The young photographers look at the heavens with fresh eyes and come up with quite delightful pictures. This year's winner Jacob Marchio (aged 14) of the USA took a stunning picture of the center of the Milky Way. There is beautiful detail in the stars and dust lanes. Jacob's photo “The Waxing Crescent Moon” was also highly commended — in that one, he got a very sharp image of a three-day-old Moon.