Earth Temple(Headstone Island): The sage is Medli. She is on Dragon Roost Island. To find her, go to the Rito village and go to the second floor. Take the exit that's near the desk where you sort letters. When you are outside, go to your right and use the Grappling Hook to cross a ledge. Medli will be on the cliff up there. Talk to her once, then play the Earth God's Lyric to awaken her.
Wind Temple(Gale Island): The sage is Makar. He is at the Forest Haven. If you have cleared the Earth Temple and learned the Wind God's Aria, then there should be music notes coming out of the first waterfall. Use the Grappling Hook, and try to jump into the waterfall while you are swinging. If you did it right, you'll be in a little cavern behind the waterfall. Makar will be practicing in it. Talk to him once, then play the Wind God's Aria to awaken him. Remember, you need to clear the Earth Temple first.
*end spoiler* Those are the sage's locations. Hopefully this is useful for you.
neutron star: a hypothetical dense celestial object that results from the collapse of a large star. Composed mostly of neutrons.