Talk:Solar radius

According to Kuhn et al. (2004, ApJ 613, 1241), the size is: (6.9574 +- 0.0011) x 10^5 km http://www.iop.org/EJ/article/0004-637X/613/2/1241/60410.text.html Thangalin (talk) 20:01, 14 February 2010 (UTC)

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)

Change in size

Since the unit is based on the current radius of the Sun, isn't it a bit like the basis of the kilogram? Does the change in the Sun's size play a role in defining (or redefining) the unit? Could someone with more knowledge than I please address the issue (as to whether or not the unit's defined measurement changes) in the article? Coinmanj (talk) 22:31, 1 December 2015 (UTC)

Mistaken explanation

There seems to be a widespread misconception about what this article is about. I don't think the lede is adequate in its explanation that the nominal solar radius is a unit of distance which was historically derived based on the Sun's radius, but is no longer dependent on it. That is, the Sun's radius varies, the nominal solar radius does not. Clearly, the lede fails to indicate that this article is about a unit of distance (the nominal solar radius) and not about a physical dimension of the Sun (which varies over time and is generally increasing).

It might also be useful to mention that the optical depth of 2/3 was chosen because it greatly simplified some of the equations involved in modeling the optical characteristics of a luminous ball of gas. (Using the Eddington approximation, it reduces (T/Te)^4 = (3/4)(τ+2/3) to (T/Te)^4 = 1 ��so T/Te = 1. Where T is the Temperature of the emitting surface and Te is the temperature of a black body emitting the same amount of energy.)173.184.23.223 (talk) 19:19, 26 December 2017 (UTC)

A sentence "fragment" (which should probably be fixed)

These comments are based upon -- (they are as of) -- the "Latest revision as of 16:18, 17 January 2020" version of this article.

The first two sentences of the "Examples" section of [that version of] this article say:

Solar radii as a unit are popular when talking about spacecraft moving close to the sun. Two spacecraft in the 2010s.

Actually, maybe we should call that "second" one a sentence "fragment" instead of a "sentence" (at least for now ... until someone fixes it).

My guess is: that the intended meaning was probably:

Two spacecraft did so in the 2010s.

...which, in context (right after the preceding sentence [q.v.]) would if I got it right mean something like this:

Two spacecraft moved close enough to the sun during the 2010s to be considered as -- that is, to "count" as -- [good] examples of venturing so close to the sun that their missions would tend to popularize the topic of solar radii ("R_☉") as a unit.

Now, that guess could be wrong. (If I'd had more confidence in how "educated" that guess was, then I would probably have edited the article promptly, instead of requesting comments here [on this "Talk:" page] first.)

Any comments? (e.g., about [a] whether or not the intended meaning was what I guessed ...OR about [b] whether or not the above [stab at a] translation is a correct [and useful] translation of the meaning of the two words ["did so"] that I think should probably get added to the sentence [fragment] we are discussing) -- ? --

Thanks for any help or advice.--Mike Schwartz (talk) 08:55, 28 February 2020 (UTC)

Equatorial and polar radius

Equatorial and polar radius are different due to rotation. Equatorial radius is largqer than polar radius about 10 km. This information must be present. Voproshatel (talk) 07:23, 20 August 2022 (UTC)