Terry Uyeki (Member 49,009) caught sight of this beam stretching across the evening sky in Podgora, Croatia and wondered if it might be an anticrepuscular ray.

Anticrepuscular rays are beams of light and shadow cast right across the sky when the Sun is low behind you. The effect of perspective means the rays appear to converge to a point on the far horizon away from the setting or rising Sun. With this in mind, do you think Terry spotted an anticrepuscular ray here?

We think this is in fact a crepuscular ray, not an anticrepuscular one. These are the ones you see emanating from the Sun, which here appears to be just over the horizon ahead, as indicated by the way the tall clouds there have their shadowed sides towards us. Crepuscular and anticrepuscular rays are caused by clouds casting shadows that are rendered visible by haze in the atmosphere. In the case of crepuscular ones, the beams fan out – again due to the effect of perspective – as the light shines towards you.
 
If you, like Terry, are ever in doubt, check the Sun’s position. If you’re facing it, they’re crepuscular rays, but if your back’s to the Sun, they’re anticrepuscular.