Talk:Parsec

Precision

“ It is therefore 360×60×60/2π AU = 206,264.806 247 AU = 3.085 677 581 31×10¹⁶ m = ~3.26 light-years. ”

I was trying to correct the precision of this calculation, but I think it is only a (close) approximation anyway, using the fact that tan(θ)~=θ for small θ. So, I have trimmed the number of significant digits.
Ray Spalding 17:49, 19 Mar 2004 (UTC)

The computation offered here is not immediately clear. I think the use of the approximation tan(θ) ~= θ for small θ is acceptable here, but we should either mention this as a whole, or leave out any form of computation. I prefer the latter, that is, to just state that a parsec is approximately ... km / miles / etc . without any calculations.

Maurice Termeer 08:21, 27 Mar 2006 (UTC)

4,000,000,000,000,000 kilometers?

4,000,000,000,000,000 kilometers doesn't fit here, does it?

3.08567758 E+16 m = 4,000,000,000,000,000 kilometers is not correct. First of all there are two too many zeros. Secondly, if 1 km = 1000 m then the result would start with a 3, not a 4.

3.08567758 E+16 m = 30856775800000000 m = 30856775800000 km

Or am I missing something here???

Midavalo 8 March 2006

"The only star in its cubic parsec"

The Sun is currently the only star in its cubic parsec—this could be taken multiple ways:

• a sphere of that volume centered on the Sun: true since such a sphere has a radius of 0.62 pc and Proxima Centauri is about 1.3 pc away
• any cube centred on the Sun: distance to any vertex = 0.87 pc, so still true however we orient the cube
• a cube not centred on the Sun: opposite vertices are 1.732 pc apart, so there's plenty of room for the Sun and Proxima Centauri if we choose the right cube, in which case the statement isn't true.
• a sphere not centred on the Sun: diameter is 1.24 pc, i.e. slightly too small, so the statement is true wherever we place the sphere.

So as well as its cubic parsec being undefined, the statement isn't even necessarily true. Musiconeologist (talk) 15:53, 16 January 2025 (UTC)

We could state, more simply and unambiguously, that there are no stars within 1 pc of the Sun. Lithopsian (talk) 20:22, 16 January 2025 (UTC)

@Lithopsian It's meant to illustrate the use of cubic parsecs as a unit of volume, though. Maybe something to the effect that our region of the Galaxy contains approximately 1 star per cubic parsec, or whatever the correct figure is? Musiconeologist (talk) 20:39, 16 January 2025 (UTC)

That would make more sense, statistically speaking, if you can find a source. One star is hardly as good way to define a density value such as this. Otherwise, adding that this cubic parsec is centred on the Sun would be unambiguously true regardless of whether it is a cube or a sphere. Lithopsian (talk) 21:18, 16 January 2025 (UTC)

@Lithopsian The whole section is horrible, to be honest. The sentence is out of context anyway, in a paragraph talking about cubic gigaparsecs, everything is very laboured, and the same rather pointless footnote is repeated several times. I think all that's really needed is a brief mention of one thing at each scale. Musiconeologist (talk) 22:06, 16 January 2025 (UTC)

Well, maybe not quite as horrible as I made out in that comment. But it's a bit of a mess. Musiconeologist (talk) 22:08, 16 January 2025 (UTC)