What's "the dawn of [something]" mean?

What's "at hand" mean?

"At hand" means close or about to happen, or it can mean nearby and readily accessible! Ex: I always have my wallet close at hand in case I need it. Ex: Her birthday is at hand, and I haven't gotten her a gift.

What does "drop someone off" mean?

To "drop someone off" refers to the action of taking someone to a place and then leaving them there. "Drop off" is the opposite of "pick up". Ex: She dropped off her daughter at school. Ex: They were dropped off at the airport an hour and a half before their flight.

Why is 'on' being used here after 'back'? Does this 'on' give a specific nuance to the sentence?

"On" here is an adverb that modifies the verb "sewing". "On" here indicates that his arm was sewn so that it is attached to ("on") his body again. "On" is placed after "back" because "back" indicates that his arm is being re-attached, meaning it used to be attached. Here are some examples of "on" used as an adverb: Ex: She put her favorite shirt on. ("On" here modifies the verb "put") Ex: He placed his sunglasses on. ("On" here modifies the verb "placed")

What are the synonyms for “check it out”?

Good question! Some synonyms for "check it out" are "take a look" "investigate" and "examine". All of these synonyms have different nuances, so make sure the word is appropriate for the situation. Ex: Can you take a look at this and see if I did it right? Ex: It seems like my computer has a virus, I should probably investigate. Ex: The doctor will examine you to make sure you are well.

I've heard that much of astronomy terms are named after Greek Mythology. Then, does "Pluto" a Greek name as well?

That's right! "Pluto" comes from an ancient Greek word. It's actually the name of the Greek and Roman god of the underworld. Ex: An eleven-year-old girl named the planet Pluto. Ex: Pluto is the farthest planet from the sun.