If you are taking a photograph of a person against a sunset, almost every beginning photography book will tell you to use flash otherwise you will end up with a silhouette of your subject against a bright background. For some reason while photographers are happy to pop some flash at human subjects, we often avoid it for natural subjects. Maybe it's out of a sort of purity; we feel obliged to use only natural light on our natural subject. It's a lost opportunity, however. There is nothing natural about the limited contrast range of a camera's sensor or a film's emulsion. Using some flash will often make a scene look a lot more like it looked when you were there and it gives the photographer the opportunity to make shots like the above which would otherwise be impossible.
The latest flash technology makes this almost mindless too. The above photo was taken with a tripod-mounted Nikon D700 and a 14-24 f/2.8 lens zoomed out to about 17mm. The light on the rock and the sliver of ice under it comes from an SB900 flash hand-held to camera left and a little low. The flash is syncing wirelessly courtesy of Nikon's CLS wireless i-TTL system. The beauty of this system is it frees the flash from the hotshoe—the worst place for the flash in most cases—without a mess of wires while still allowing the camera to control the light from the flash at the moment of exposure. You can move the light around, shoot through modifiers, bounce the light all while the camera keeps the flash exposure relatively constant. The flash has a warming gel (the SB900 comes with a nice little gel holder) over it since introducing a neutral white light into a sunset is going to look artificial and a little clinical. Despite the bright background, the camera wanted to overexpose the sky a bit so I dialed in -2/3 exposure compensation. This is a global exposure change so it also changes the flash exposure. In this case I wanted a little more out of the flash so I bumped the flash compensation up 1/3 stop—just enough to pop off the reflective surface of the rock and bring out that wonderful streak of blue in the ice underneath it. The camera did all the rest. From the time the tripod hit the ground it took less than a minute.