So Wolfram Alpha and Wikipedia are giving me two very different values for the distances of certain stars.

[SMJB]

Just based on the reputations of both sites, I'm inclined to believe WA more, but it'd be nice if I had more to go on than that, so...what sites should I trust with this? Mind you, the ultimate goal is to know the distance from one star to another, so sites that can do that for me would save me a lot of work.

[Gaidin]

Ok. The question of the day is not why you're now going to wikipedia, but what is wikipedia citing? That's where you start untangling this mess.

[SpottedKitty]

Even with all the measurement techniques we have nowadays, there's still a lot of wiggle room and uncertainty in stellar distances. There are exceptions such as Cepheid variables and Type 1a Supernovae, both of which are predictable enough in their behaviour to be used as standard candles out to intergalactic ranges, and anything close enough to be measured directly by parallax, which is only good for a few hundred parsecs. Which stars were you looking at?

[Enigma]

So you want a definite answer to a very vague question? What stars? Do you mean the distance between Johnny Depp and Robert Downey Jr? BE. MORE. SPECIFIC.

[Adam Reynolds]

Now this is really making my curious, what stars were they?

[Fingolfin_Noldor]

I am going to come out here and first ask for links and ask what is the methodology used to measure the distances. As far as I know, the usual way of measuring distances is using an interferometric telescope setup and relying on the coherence length of the light sources to measure the distance.

[SMJB]

I'm looking at stars ~15-20 lightyears from Sol and ~10 lightyears from Tau Ceti.

Wikipedia has a list of the closest stars to Earth*, and Wolfram Alpha has a function where you can type "distance from X to Y" and it'll calculate it**, assuming you use a star name it recognizes (it's particularly bad at the Glieses, in my experience--keeps thinking you're talking about asteroids).

* https://en.wikipedia.org/wiki/List_of_n ... own_dwarfs
** for example: http://www.wolframalpha.com/input/?i=di ... o+HIP+1242

[Napoleon the Clown]

So... Where are you getting conflicting answers? Because that Wikipedia link doesn't seem to give distances between the stars in question, just their distance from Earth. And, um, stars are arranged in three dimensions. They're not all lined up in a nice, pretty line.

I decided to be super, duper nice to you and look at the WA calculation for the distance between Earth and HIP 1242, then compared it to Wikipedia. Here's a hint on figuring out which one is reliable: Check the citation linked for the Wikipedia article and see if it has the distance anywhere. (It does not.) This is why you need to actually read the damn citations instead of going "Eh, sounds reputable."

By using a bit of Google, I find a website that gives the distance to HIP 1242 in parsecs, and when I multiply that out into light years the number agrees with WA. So, um, use WA.

[SpottedKitty]

Hmm, well, if you're talking about tiny distances like that — not even 10 parsecs — then parallax measurements are going to be pretty accurate. Note that, as always with Wikipedia YMMV (literally in this case), so you'd be best to dig out some original data sources.