This image shows the International Space Station and Space Shuttle Atlantis on the last ever Shuttle mission STS-135 while they enter the Earth's shadow over the Pacific Ocean at 19/07/2011 18:25 NZST.
The ISS and Atlantis undocked from each other just 3 minutes later at 18:28 NZST. This marks the last time that a Space Shuttle docked at the ISS, as well as the last ever Space Shuttle flight of the U.S space program.

During the 5 minute exposure clouds rolled in and obscured parts of the ISS path after the pair had faded from view, but this added a rather nice overall effect to the image.

These were the events taking place during and immediately after this exposure, as covered by spaceflightnow.com:

0623 GMT
Five minutes from undocking. The steering jets on Atlantis are inhibited for the period of physical undocking from the station. The separation occurs when large springs push the two craft apart. Once the shuttle is a couple feet away from the station and the docking devices are clear of one another, pilot Doug Hurley will fire Atlantis' thrusters to continue the movement away.

0625 GMT
The spacecraft are nearing an orbital sunset. The undocking will occur in darkness but the later flyaround of the station by Atlantis will take place in daylight.

0626 GMT
Hooks and latches are driving open.

0628 GMT
UNDOCKING! The final space shuttle parts company with the International Space Station, a sentimental sendoff for America's winged machines that spent the past decade constructing the million-pound science complex and supplying the orbiting laboratory with vast loads of logistics. In 37 missions, the shuttles spent 276 days, 11 hours and 23 minutes docked at the station.
With the shuttles entering forced retirement, the space station now must rely upon Russian, European and Japanese unmanned cargo freighters for continued support. U.S. commercial servicing missions by SpaceX and Orbital Sciences are planned to start by next year.
And the Russian Soyuz becomes the sole means of launching astronauts to the station and returning them to Earth. The American effort to develop a new human spacecraft to replace the shuttles remains years from taking flight.
The food and equipment delivered by Atlantis ensures the space station has enough provisions to support a full six-person resident crew for the next year while awaiting the U.S. commercial firms to get the routine resupply missions underway.

0630 GMT
After 8 days, 15 hours and 21 minutes of being linked together high above Earth, shuttle Atlantis undocked from the International Space Station on-time at 2:28 a.m. as the two spacecraft flew 243 miles over the Pacific Ocean, east of New Zealand.