Maybe you know, but it is kind of a love/romantic thing. I don’t think it is ever used about 2 dudes sharing an umbrella, haha (unless they are gay of course).
Edit: also there is the meaning of a drawing where you draw an umbrella with your name on the left side and the one you have a crush on/love on the right side.
The word “planet” comes from the Greek for “wanderer” so it’s not that far off, though we don’t call asteroids “little planets” the way Japanese does. I guess we think of them as little stars (the “aster” part)
じてんし or bike, learned from Rosetta Stone. I learned it yesterday and today I was riding my bike and thought of it! It was cool. Not sure what the kanji is for it.