Spanning the heavens

[Erbab]

Hi!

This sentence is from Cambridge Practice Tests for IELTS book.

"At the rise of the star Sirius just before sunrise, which occured around the all-important annual flooding of the Nile, 12 decans could be seen spanning the heavens."

I don't understand the bold part.

 

[Skrej]

Have you tried looking up 'span' in a dictionary? It should make sense if you understand the word 'span'.

hint: if you need to look up 'heavens', look for the non-religious definition.