Why Do Tiny Objects Appear Brighter When Backlit?

[Cato]

Why are tiny objects, such as floating dust in the air, so bright when they are lit from behind and not at all bright when they are lit from the front?

 

[davenn]

Why are tiny objects, such as floating dust in the air, so bright when they are lit from behind and not at all bright when they are lit from the front?

really ?
I generally find that silhouetted objects to be very dark - black
and I make use of that feature when doing photographyDave