John W. Campbell 
The Ultimate Weapon [EPUB ebook] 

The star Mira was unpredictably variable. Sometimes it was blazing, brilliant and hot. Other times it was oddly dim, cool, shedding little warmth on its many planets. Gresth Gkae, leader of the Mirans, was seeking a better star, one to which his ‚people‘ could migrate. That star had to be steady, reliable, with a good planetary system. And in his astronomical searching, he found Sol…