While reading through a physics textbook, I came across the use of sub-scripted ☉s.

Here's the context:

Stars between 0.5M and 10M will evolve into red giants...

I'm assuming it's to do with the life-span of a star; however, I don't know exactly how.

I searched google/wikipedia however it simply stated it represented the sun

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    $\begingroup$ solar mass $\endgroup$ Commented Nov 20, 2016 at 17:28
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    $\begingroup$ I really don't understand why this was down-voted. $\endgroup$
    – Tobi
    Commented Nov 20, 2016 at 17:31
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    $\begingroup$ I didnt downvote, but I guess the reason is that you didnt really show any research effort. $\endgroup$ Commented Nov 20, 2016 at 17:32
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    $\begingroup$ And what you found when you searched is exactly right and the answer to your question. $\endgroup$ Commented Nov 20, 2016 at 17:57
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    $\begingroup$ I do not at all believe that this symbol is not defined in the textbook previous to its use. At worst, there will be a table at the very beginning of the book. $\endgroup$
    – Kyle Kanos
    Commented Nov 20, 2016 at 18:27

1 Answer 1


The symbol in question, $\odot$, usually denotes the Sun. The solar mass, $M_\odot$, is often used as a unit of mass in astronomical/astrophysical texts. Another example is the solar luminosity, $L_\odot$.

  • $\begingroup$ Does 1M⊙ represent the mass of the sun? $\endgroup$
    – Tobi
    Commented Nov 20, 2016 at 17:36
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    $\begingroup$ It's exactly as it's written in the answer above. No need for a 1 in front and a subscript symbol for the sun. $\endgroup$
    – user108787
    Commented Nov 20, 2016 at 17:39
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    $\begingroup$ Just in case it's not clear, "solar mass" and "mass of the Sun" mean exactly the same thing, represented by the symbol $M_\odot$. $\endgroup$ Commented Nov 20, 2016 at 17:50

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