Talk:Solar radius

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Do we really need this page, should it not just be part of the main sun arcticle.—Preceding unsigned comment added by 144.82.106.36 (talk • contribs)

This article should be kept separate because it is about a unit of measurement and not about the Sun itself. To merge it would be like merging kilogram to platinum or iridium just because the kilogram is still measured according to a block of platinum-iridium alloy to this day. Flyingtoaster1337 04:05, 25 January 2007 (UTC)

Yes, keep it. The "solar radius" unit sometimes causes confusion, because there are published evolutionary tracks for the Sun where the radius is tabulated in solar radii ... and because the unit is fixed at the current value but the sun does change size, in general the radius of the Sun in those tracks is not 1.00 solar radii. BSVulturis (talk) 18:24, 8 February 2008 (UTC)

I'm having trouble understanding this simple concept. I was trying to compare the sizes of the Sun, Arcturus, Betelgeuse and VY Canis Major. I googled for other sources and found only deeply technical pages.

1. Why is radius used instead of diameter? 2. A list of accurate size comparisons between the Sun, other stars and the giant stars would be great. 3. A connection or explanation (if possible) between increase in size and the resulting increase of mass. 4. If I trusted my understanding of this concept I could make an illustration for wikipedia showing the relative sizes. (my 8th grade science students really enjoyed my preliminary illustrations) 76.172.113.10 (talk) 01:24, 28 March 2008 (UTC) WNettles 3 March 2008

1. The solar radius unit is chiefly used by practitioners in the stellar astrophysics business. In a number of the equations for computing stellar structure, the best variable to specify is distance from the center. Consequently, the solar radius rather than the solar diameter is the "most natural" yardstick with which to specify stellar sizes.

2. Direct measurements of stellar size in linear units are rare, limited to eclipsing binary stars with good double-lined spectroscopic binary orbit solutions. Stellar sizes usually are computed from an angular diameter and the stellar distance, each of which have their own uncertainties. Such stellar sizes can be computed fairly easily, but I'd have to do some rooting about on the Web to find a list of sizes that I could verify were done right in order to link that as a data source.

3. This can't be done, except in a very general way for quite restricted evolutionary stages of stars. Stellar radius varies with time for any star because of stellar evolution. A consequence of this is a given stellar radius happens for an enormous range of stellar masses, but at different evolutionary stages. To see this, look at a Hertzsprung-Russell Diagram; in the theoretical version of that, whose axes are log luminosity versus log surface temperature, one particular value for the stellar radius corresponds to a diagonal line in that diagram.

4. I think that's well worth doing! I'll see if I can find a useful page of stellar radii and link it here.

BSVulturis (talk) 19:09, 30 April 2008 (UTC)