Star trails are photographed by pointing a camera skywards and waiting. As the Earth rotates, stars produce circular trails.



This image was shot over Yosemite falls in Yosemite National Park, California. The long exposure gives the illusion of daylight, but it's actually the light of a full moon that is creating a rainbow in the mist. The image was constructed from 500 individual photographs shot over several hours.



(Image: Jeffrey Sullivan)

This bright streak across the night sky was caused by Japan's Hayabusa spacecraft returning to Earth in June 2010. It was returning from a seven-year mission to visit the asteroid Itokawa. Hayabusa touched down on the surface of the asteroid in 2005 and brought dust samples back to Earth, landing safely in the Australian outback.



Other spacecraft had visited asteroids before, but this was the first time that material from one had been returned to Earth.



(Image: Kouji Ohnishi)

The Orion nebula, at the right of the image, is the closest region of massive star formation to Earth and can be seen with the naked eye.



To the left of the image, the bright stars of Orion's belt can also be seen. In addition, the tiny silhouetted Horsehead nebula is just visible against the pink hydrogen clouds just left of centre.



A nebula is an interstellar cloud of dust and gases. Many nebulae form as the interstellar medium collapses under its own weight. As the material shrinks, massive stars form. Ultraviolet radiation emitted by these stars ionises the surrounding gas, making it visible to telescopes back on Earth.



(Image: Fabian Neyer) Advertisement

The northern lights, or aurora borealis, are a natural light display caused by highly charged electrons in solar wind interacting with the Earth's atmosphere.



Solar winds stream away from the sun at speeds of around 450 kilometres per second. Upon reaching the Earth, some 40 hours later, they follow the lines of magnetic force generated by the Earth's core and flow through the magnetosphere, a teardrop-shaped area of highly charged electrical and magnetic fields. The electrons in the solar wind then interact with oxygen and nitrogen in the Earth's upper atmosphere, producing spectacular light displays.



In the southern hemisphere, the analogous phenomenon is known as aurora australis.



(Image: Christian Salomonsen)

This image shows the Milky Way rising over the village of Oneroa on the coast of Mangaia in the Cook Islands. It is a spiral galaxy, and our solar system sits in a spiral arm known as the Orion-Cygnus arm.



The Milky Way contains something between 200 and 400 billion stars, and is estimated to have at least 50 billion planets. It takes our sun 225 to 250 million years to complete a full orbit around the centre of the galaxy.



Its name comes from Greek mythology. According to legend, the galaxy is milk spilt by Zeus's wife Hera while suckling the infant Heracles.



(Image: Tung Tezel)