Hola Rivkah

Generally we use "en el.., en la..." to say "in the../on the.." but with sol and sombra (sun and shade) the set expression is "al sol" and "a la sombra": in the sun, in the shade.

You may also use "en el sol" and "en la sombra" though, that would also be correct. 

Saludos

Inma