On the Japanese calendar at left, I have covered up 24 instances of the same kanji (character) with blue boxes. These usages of the kanji refer to particular periods of time, but the same kanji can also refer to what object in space?
Hint
The only language you need to know for this puzzle is English.
Bonus Puzzle
If you can read kanji—or Chinese!—then today's puzzle may not be much of a puzzle at all. Try this one instead. Why are these 12 kanji called ghost characters?
As for the bonus puzzle: Even if you can read kanji, you should be puzzled by these 12 characters, because they are literally meaningless. In the 1970s, a committee produced a set of over 6000 kanji to be digitized for Japanese computer fonts. But they made a few mistakes, and ended up including 12 kanji that (as far as anyone knows) had never been used before. Now that those kanji are available on computers worldwide, people have jokingly suggested various meanings for them, while scholars have investigated how the errors were made. Read the story.
Incidentally, English has had its own ghost words. A major dictionary was supposed to have an entry defining "D or d" as abbreviations for "density", but someone goofed, and the result was the word dord.
Solution
The kanji is used in two different ways on the calendar, to mean month and Monday. But just as in English, both of those words are derived from… the Moon!
Congratulations to yesterday's solvers Tori, Alex Z., Max, Maddy, Nico, Nicholas, Yana, Anna K., Peter V., Bridget, Jacob C., Atticus, Jason, Graham, the Greggs, and Dr. Yetman. Thanks to everybody who made a guess!