Wow, thank you! <3 Hal is a masculine name (and I pretty much go by it all the time) but if I say my name is Halley, people just tend to assume I'm a girl. I really thought it was a gender neutral name... I'm autistic so I can't tell as easily as other people lol. I guess my advice is: when you've picked your name, ask other people whether it reads as fem or masc! I know you're cis but it can still be really annoying for people to assume you're a gender you're not because of your name.
I wanted a science-based name because I'm a little nerd lol. I considered Kelvin at some point. In the end, (and I really can't remember why I specifically chose it) I named myself after Edmond Halley -- Hal as a nickname, as a reference to HAL 9000 of course.
Honestly, I sort of regret it, because Halley isn't as gender neutral as I thought and everyone considers it a girl name. I wish I'd been more out there and straight up decided to call myself Truck or Brick or something.