Space 01
Why Are Auroras Different Colors? Green, Red and Purple
Green and red auroras come from the same oxygen atom. A 0.75 s vs 134 s lifetime and air density decide which colour wins. The physics, with worked numbers.
sun
Space 02
Why Is the Sun's Corona Hotter Than Its Surface?
The corona is 1 to 2 million K above a 5,772 K surface. Why that breaks no law of physics, how little energy it takes, and what Parker Solar Probe has found.