Can only be seen at night
Strongest bound nucleus among all elements.
Burn in the atmosphere.
Planets outside our Solar System.
All stars and planets have orbits
Came from comets in outer space.
When the sun first shone.
Shields from cosmic radiations
The moon doesn't radiate.
Days getting longer.
Planet orbiting multiple stars.
Coronal mass ejections.
Luminosity varies with stage.
Distance in light-years.