I hate these silly made-up words for non-existent phobias, and my ire is particularly invoked on ones like Walloonophobia 'fear of Walloons' and angrophobia 'fear of anger'. Since anger is a Norse borrowing, this more than usually violates the principle that if you're going to make up words, try to have the courtesy of making them up in Greek. So fears of railways and peanut butter have respectable-looking Greek elements.
I find someone has stuck the Latin sidus, sideris 'star' into the sausage machine and created siderophobia 'fear of stars'. Now not only is there a much more familiar prefix astro-, which happens also to be Greek, but sidero- is Greek for 'iron'. Siderophobia is a perfectly good word for 'fear of iron', but a rotten one for 'fear of stars'.
The Latin and Greek roots are quite different: Latin [si:des-], Greek σιδηρ- [sidε:r-] with different vowel lengths. The medial [r] in the Latin is coincidental, since it derives from [s] by a familiar sound change in Old Latin.
Could they be related more deeply? In researching this I found to my astonishment that the meek and mild word consider is in this lot, etymologically 'consult the stars'! Wow. Add that to disaster and the other one I always forget.
Anyway, Perseus reckons they are connected... no, wait, it says 'cf.', that just means they think it looks suspicious. Well the common IE group they're connecting Latin sidus to is 'sweat, melt': English sweat, Sanskrit svid- 'sweat, melt', Greek sidε:r- '(molten) iron', Latin sud- 'sweat'. Hmm. So we need two Latin developments, one with *[s] and one with *[sw]. Well the Greek for 'sweat' is hidr-, so that fits *[s], and pre-Greek *[sw] became Greek [s], so that fits. But why the long vowel in sidus? Did you get compensatory lengthening for loss of *[w]? It doesn't look right. In fact it looks a bit like a coincidence that some old etymologist has tried to straddle with thoughts of meteoric iron.
Well I don't know, maybe the experts say this is okay and there are such correspondences, but it doesn't look right to me. But then where does si:der- or si:des- come from? Because it looks sort of like 'star' too but not enough to make sense. The PIE was *Hster, English star, Greek aster, pre-Latin ster-la, and you can't get a [d] out of that, nor a long [i:]. The way Perseus phrases their quotes it seems that sidus originally meant 'constellation' rather than an individual star.
This would all be private intra-brain mumbling/ignorance if I hadn't discovered that bit about consider.