You may've noticed an ugly gap in the horizon during your inworld travels. This is considered a bug; SL-24381 is the internal issue key as filed by Dan Linden. This often makes an otherwise-beautiful picture look unsightly.

In a number of situations, you'll want to prettify the situation by turning rendering of the "Ground" OFF, so your piccies look more like the examples on the right:

How?

First, if it isn't already open, press Ctrl-Alt-D to make the Client menu appear at the top of your screen.

Then, go to Client menu > Rendering > Types > Ground. Notice there's also a convenient shortcut for it: Ctrl-Alt-Shift-8.

You should see the gap disappear. If there's an especially prominent sun or moon in the distance, the difference should be strikingly apparent, and the full gradient that accompanies it won't be truncated. A sunset, in particular, will have even more of a visible, specular glow.