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I have come across the sentence that I cannot get. it is from Crash Course Astronomy (it is at around 1:40). Here is the sentence:
Oxygen tends to glow green, but to a lesser extent give blue light too. Other elements span the spectrum in colours they give off.
Some dictionaries say span means to include something, but still I cannot get. Could you please rephrase the sentence for me please?
to span something is like a bridge: it goes across a particular area. Other elements go across the spectrum in the colours they give off.
To span: to go from from end of something to another side.
Like a bridge: a bridge spans a river. It goes from one side of the river to the other. Now, substitute spectrum for the river.
The colours go from one end of the colour spectrum to the other end. Humans can only see part of it. It is called the visible colour spectrum.
"Span" as a verb means to include, especially to include over some range or across boundaries. Like we might say, "Possible values span the range from 1 to 10", meaning that the "values" can be any number between 1 and 10.
In this case, there are many colors that an element could give off. Some elements give off only one color, others "span" many colors.
Elements (in space) give off different colours of light. One meaning of "span" is "Extend across". So the different colours of light given off by different colours extend across the spectrum from Red to Blue
It just means that all the different colours are given off by some elements in space.
