Talk:Selûne (moon)

Distance discrepancy
The distance between Toril and Selûne given in the Forgotten Realms Campaign Setting 3rd edition is quite bizarre. It says that it is 2000 miles across at a distance of 20,000 miles (for comparison, Earth's moon has roughly the same diameter but lies at a distance of 238,000 mi).

Astronomically, that doesn't make sense. An object of that size that close would have an angular diameter of 5 degrees. That's ten times larger than our moon appears in Earth's sky! (Again, for comparison, Earth's moon has an average angular diameter of around 0.5 degree.)

On the other hand, Realmspace puts Selûne at a much more reasonable distance of 183,000 miles, which, for an object of the same size, would result in an angular diameter of 0.6 degree. Larger than our moon, as is stated in multiple sources, but not by much. Even magic must give way to geometry. :)

Is there any other source that corroborates the weird 20,000 miles? If not, I think it should be considered a typo, and the value from Realmspace should be adopted instead. &mdash; Sirwhiteout (talk) 01:10, January 30, 2018 (UTC)


 * I'm betting that should have been 200,000 instead of 20,000 miles, which would make it appear a bit larger than Earth's moon. &mdash;Moviesign (talk) 01:42, January 30, 2018 (UTC)


 * That was my first thought as well, but I'm afraid it's even worse. Further down, the FRCS also explicitly notes that Selûne can be covered by a typical human fist held at arm's length. This is consistent with an angular diameter of 5 degrees or less. So it could have been on purpose…


 * One possible way to resolve this discrepancy is to find any source other than Realmspace that states the distance between the Tears of Selûne to Selûne itself. Realmspace puts the Tears at 183,000 miles from the moon, which would be consistent with the FRCS statement that they appear up to 60 degrees apart from Selûne in Toril's sky, but only if the distance between Selûne and Toril is also 183,000 miles.


 * Also, we could consider the relative apparent sizes of Selûne and the sun. The sun is stated as an H-sized body, so it would be at most 1 million miles in diameter (Earth's sun is 864,000 miles across, also in the high end of the H category), and its distance from Toril is measured at 200 million miles (on Earth, an astronomical unit is 96 million miles). That would give it an apparent diameter of at most 0.3 degrees, so half of Selûne's smallest diameter. That's ok, and is consistent with there being no annular eclipses on Toril, as stated in FRCS, but a moon that appears to be over 16 times larger than the sun is quite remarkable. &mdash; Sirwhiteout (talk) 02:14, January 30, 2018 (UTC)

Off Topic
Just FYI, tonight and tomorrow morning (January 30–31, 2018) will be a super moon (moon close to Earth), a blood moon (partial lunar eclipse in the morning), and a blue moon (second full moon in the month). Take a look if you can. &mdash;Moviesign (talk) 20:06, January 30, 2018 (UTC)


 * I also sent this link to my students: the eclipse will be streamed live by NASA, which is useful since here in Ontario we will only be able to catch its very beginning. Happy skywatching! &mdash; Sirwhiteout (talk) 21:44, January 30, 2018 (UTC)