The warm, emotional light in photography.
BACK LIGHT: Avoid the sun directly behind your subject
Back lighting is wonderful but there are two tricks to making it look great.
1. Your subject has to be slightly off-center from the sun. Face the sun. Your subject needs to be no more than about 15-20° from being directly from the sun.
In other words, f your sun is "noon" as you face it, your subjects should be at about 10:00-11:00 or 1:00-2:00. This will give you rim and backlight, not side light. sAny more than that and your subject becomes side-lit. That will not create backlighting or rimlighting. Subjects directly under the sun, if the sun is too bright, will be more difficult to photograph and capture the rim lighting.
Additionally, you want your subjects to be below the horizon (or at least not up against the bright part of the sky). Otherwise you get silhouettes and not rim and backlight.
Be SURE that your background is darker or the "rim" of the rim light will not appear. Notice the light areas outlining parts of the horses legs and the girls' hair. You need contrast (darker background) to make that show up well.
RIm Light and Back Light:
Notice in this image, the backlight is caught by the dust and creates exceptionally lovely contrast. The horse's necks and manes are lit (outlined) by the sun above and behind them that catches on their fur and hair.
Rim Light and Side Light:
In this image of a cowboy whose face is light by the fire in front of him, you can notice the rim lighting as well on his face. This is done by a flashlight low and behind him, just touching his face from the back. The rest is light from the fire at night.