Talk:Parsec
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- 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(a)~=a for small a. So, I have trimmed the number of significant digits.
Ray Spalding 17:49, 19 Mar 2004 (UTC)
Parsec
For the non-astronomers among us, how many miles is a parsec? From a crossword puzzle clue, I'm guessing 19 billion miles. Is that right?
One lightyear = ~5.88 × 1012 miles
One parsec = ~3.26 lightyears
= ~(3.26 × 5.88) × 1012 miles
= ~19.2 × 1012 miles
So if you're talking British billion, yes that's right. If you're talking American billion, then no. It would be 19.2 trillion miles in American trillions. -- Derek Ross | Talk
- Make that 'Traditional British billion' rather than 'modern British billion'. The Government and BBC would call the above number 19.2 trillion miles - see long scale for further information. Ian Cairns 19:23, 26 May 2005 (UTC)
Picture not to scale
I would recommend adding some kind of notice that the picture [1] (http://en.wikipedia.org/wiki/Image:Parsec.png) depicting the method of how to calculate a Parsec is not to scale. I think it would be great if it could be added directly into the picture, but a note in the text would be fine, too.
--capnez 18:17, 4 Mar 2005 (UTC) 13:05, 4 Mar 2005 (UTC)
EDIT: Updated my signature, I finally got an account!
![[1]](http://en.wikipedia.org/wiki/Image:Parsec.png){kind=link}
Discrepancy in Parsec Definition
There is a discrepancy on this page in the definition of a parsec. Near the top, it states: "The parsec is defined to be the distance from the Earth of a star that has a parallax of 1 arcsecond." But on the diagram towards the bottom, the parsec is labeled along the side of the triangle (which is the distance between the Sun and "D"), implying a parsec measures the distance between the Sun and another object, not between the Earth and that object.
Something doesn't add up. These two distances are quite different. What is the exact definition?
Globe199 13.00, 26 May 2005 (CDT)
- Well, distance from the Solar System is the point. An object 1 parsec from the Sun is 206,265 AU away. Its distance from the Earth is 206,265 ± 1 AU; I wouldn't call that "quite different".
- —wwoods 18:56, 26 May 2005 (UTC)
- OK, so you're saying it doesn't really matter, since the distance is almost the same; we're talking about distance on a galactic scale, so ± 1 AU is negligible. Sounds good. On the other hand, at what point is parallax useless? The page on Deneb says the distance is between 1600 and 3200 light years because "...determination of distances at this range is very difficult because stars with such distances have negligible parallax."
- Globe199 15.57, 26 May 2005 (CDT)