Meaning “dawn”, an aurora is a visible glow of variable Basic property used to characterize stars, luminosity is defined as the total energy radiated by a star each second. An object’s luminosity is often compared to that of the Sun (Lsun = 4 × 1033 ergs/s = 3.9 × 1026 Watts). Luminosity has the same units as power (energy per Click on Term to Read More and color in a planet’s Region of charged particles in a planet's upper atmosphere. The Earth's ionosphere is at an altitude of ~40-400 km. Click on Term to Read More caused by the interaction of charged particles (typically of solar origin) accelerating through the planet’s magnetic field. A well known example of this phenomenon is the Aurora Borealis, also known as the Northern Lights.