하늘에서 별 따기 sky-ABL star pick-GER […like] picking stars from the sky
Which is to say, trying to do something impossible. Pretty self-explanatory. I've not been very consistent in how I mark (terminologically speaking) word endings – I use so many different reference sources, and there's certainly no consensus among those sources. I sometimes think of the -에서 ending as an ablative or simply "lative" case for nouns. And there is definitely something gerund-like in the -기 ending for verbs. Hence my choices for today, above.
I have a really smart cohort of middle-schoolers. For our English listening-skills class, we use one of the highest level iBT (internet-based TOEFL / Test of English as a Foreign Language) test-prep textbooks. The topics on the actual TOEFL are often similar to the content of college-level coursework, and thus we end up talking about some pretty advanced material: geology, biology, 19th c. American literature, etc.
Today, we were talking about astrophysics. I was trying to explain Hawking Radiation, despite not being very clear on it, myself. The listening passage was one of those simulated college lectures. It was talking about XRay telescopes. One of my students was more clear on the issues than I was – XRay telescopes must be deployed in space, he noted. Like I said, these students are very smart.