They appear as gaps in the spectrum of light from distant stars and galaxies because the substances that cause them absorb those frequencies (or colors) of light in the spectral rainbow.
(They; appear; as gaps in the spectrum of light from distant stars and galaxies) (the substances; cause; them absorb those frequencies (or colors) of light in the spectral rainbow) Context(the substances cause,List([85, 110))):(them; absorb; those frequencies (or colors) of light)
the substances cause,List([85, 110))
They the substances them
appear cause absorb
as gaps in the spectrum of light from distant stars and galaxies
them absorb those frequencies (or colors) of light in the spectral rainbow
those frequencies (or colors) of light