It's my understanding that the Sun (uppercase) is used to refer to our sun/star, because it is The Sun. Latin name is Sol, hence the Solar System. Even the tag (lowercase sun) on this post has the caption "Questions regarding the closest star to Earth, at the centre of the Solar System."

Other planetary systems have their own stars, which I understand are called a sun, in the context of that planetary system.

I've tried my best to find a credible source that exoplanets indeed have their own suns, and that the term "sun" doesn't just refer to our Sun. I have only found this one website that backs this up: http://curious.astro.cornell.edu/physics/78-the-universe/stars-and-star-clusters/general-questions/346-what-is-the-difference-between-a-star-and-a-sun-beginner

It seems to be common knowledge in the scientific community that this is correct, but I can't find anything else online to back this up. Help?

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    $\begingroup$ Note that all the tag names are in lower case. $\endgroup$ – SE - stop firing the good guys Apr 25 '16 at 18:32
  • $\begingroup$ I've gotten the impression that "Sol" is not widely used, even among astronomers. It does seem to be used quite a lot by science fiction authors, though. $\endgroup$ – HDE 226868 Apr 25 '16 at 23:45
  • $\begingroup$ @Hohmannfan Indeed. That is regrettable in this case; though Sun and sun are rarely confused, moon and Moon often are. I have asked a Meta question. $\endgroup$ – Rob Jeffries Apr 26 '16 at 9:40
  • $\begingroup$ Even if Sun and sun are rarely confused can anyone point me to a credible source that actually describes the distinction? I simply can't find any... $\endgroup$ – Eric Warnke Apr 29 '16 at 1:14
  • $\begingroup$ The Sun, is a proper noun. The rules are the rules of the English language. If you wish to refer to other suns, that must not be capitalised. $\endgroup$ – Rob Jeffries Apr 29 '16 at 7:18

The technical name (in English) for the Sun is not Sol, which is just Latin for sun. The technical name for the Sun is the Sun. Another body in the sky has a similarly boring name, the Moon. There's one more boringly named object: in the Solar System: The Earth. Note the use of "the" (a definite article) and the use of capitalization to indicate a specific object.

The problem with Sun, Moon, and Earth is that we have been using these names (or their predecessors) for thousands of years. For example, sun, sol, ἥλιος (helios), and a bunch of other names for that very bright object in the sky whose presence distinguishes day from night all derive from the same proto-Indo-European word sóh₂wl̥.

As an end note, from http://curious.astro.cornell.edu/about-us/159-our-solar-system/the-sun/the-solar-system/4-what-are-the-names-of-the-earth-moon-sun-and-solar-system-beginner,

You may read or hear people using Luna for the Moon, or Terra or Gaia for the Earth, or Sol for the Sun, but in English-speaking countries, these are poetic terms, often seen in science fiction stories, but not used by astronomers in scientific writing. In some countries where Romance languages are spoken, these terms are the official names.

It's also interesting to note that most astronomers do not call our galaxy the Milky Way in technical writing--they call it the Galaxy.

  • $\begingroup$ I updated my question to refer to the Sun and not our Sun, thanks. $\endgroup$ – Eric Warnke Apr 29 '16 at 1:12
  • $\begingroup$ In terms of an answer, this doesn't actually help me though. I need a credible scientific source stating that a star can be called a sun. Apparently none exist... $\endgroup$ – Eric Warnke Apr 29 '16 at 1:13

When language developed there was a need to refer to the "the bright shiny thing that makes the days light" and to the "sparkly things in the night sky". These things were very obviously different and so received different names.

Several ancient greeks, and some renaissance Italians were executed for suggesting that the sun might be a star. And it wasn't until the middle of the 17th century that the idea that the sun was a star became "settled science". And not until the late 20th century was it apparent that other stars have their own planetary systems from which they could be viewed.

Our language hasn't really caught up. But there is nothing wrong with referring to "stars from the perspective of an orbiting planet" as suns. For example a nasa blog describes Kepler16-b as a planet "Where the sun sets twice" The important thing is to be clear, ask "would my readers know if I am referring to The Sun or a sun in this context".

  • $\begingroup$ Thanks for the comment. I'm not worried about my readers, rather trying to convince some people that it's correct to say "Where the sun sets twice". I literally can't find any authorities talking about this being correct. $\endgroup$ – Eric Warnke Apr 25 '16 at 22:06
  • $\begingroup$ There are a couple of typos where you refer to "the sun", where you should use "the Sun". Correct capitalisation of proper nouns removes most confusion. $\endgroup$ – Rob Jeffries Apr 26 '16 at 6:23
  • $\begingroup$ It is hard to speak in capitals. $\endgroup$ – James K Apr 26 '16 at 20:48

When I was very young, I didn't know that the sun in the sky was just another example of the stars I saw at night. I just wasn't surrounded by people who talked about such things. Later, when I learned that the sun was also a star, I was glad to know there was a star close enough to study. The term 'sun' was used to describe our star, even before people realized it was a star. So the term 'sun' is a generic word that might follow us to the stars and be used in everyday conversation to refer to the local day stars. 'Sol' is what the Romans would say whenever they talked about the sun. Currently 'sol' is being used to refer to a rotation of a planet other than Earth in our solar system. For instance on Mars a 'sol' is about 24 hours and 38 minutes, and on Jupiter a 'sol' would be about 9 hours and 50 something minutes. There's no reason why we can't refer to a rotation of the Earth as a 'sol', but we already call it a 'day'.

  • $\begingroup$ Please note the difference between the Sun and other suns. $\endgroup$ – Rob Jeffries Apr 26 '16 at 6:25

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