Should the sun (the big yellow hot thing, not the newspaper) have a capital letter?

[rumblethump]

is it a proper noun? and so do moon and earth need capping up too?

no

and moon def not - it's a moon the the moon

not entirely sure about Earth as there's only one IYSWIm. Think I would capitalise.

noth the moon

bah

that's what i thought. it was in capitls in a newspaper article.

and my friend seemed to think that it should be capital, like the planets Mars, Jupiter, Earth and so too, the Sun.

All the planets have capital letters don't they? So Earth is correct. If the sun had a name like Sol it would be capitalised but just saying 'the sun' 'the planets' 'the moon' - no.

it certainly used to be capitalised in say 18th and 19th century texts (maybe not later 19th c)

but then so did a lot of nouns we would not capitalise now

No, no, no.