Io keeps the same face toward Jupiter as it orbits the planet. For this reason, Jupiter appears to hang motionless in Io's sky. Just as the Earth's Moon does, Jupiter goes through phases as Io orbits it. Here's a gallery showing the view from a location in the northern hemisphere during the course of a single day. It's the kind of view future colonists might take for granted, but it's still pretty incredible for those of us who've only ever experienced days on Earth.
1. The sun has just come out from behind Jupiter while the thick atmosphere of the planet is illuminated in a glowing ring. (See above)
Click to embiggen any image.
2. A few hours later, the sun appears to have moved to the right, lighting up the landscape brightly.
3. A little over ten hours into Io's day and Jupiter is in its first quarter phase.
4. Halfway through the day, the sun is now behind us. We can see the tiny shadow of Io on the cloudtops of Jupiter.
5. Ten and a half hours later and the sun has now set below Io's horizon. Jupiter is in its last quarter phase. A distant volcano has begun erupting and the gasses it is releasing into Io's thin atmosphere are glowing in the dense radiation field that surrounds Jupiter and Io.
6. Near the end of the day and the sun is just below the left horizon. It will be rising soon only to disappear again behind Jupiter.