The Sun isn't a star, in Equeria it's a planet. It's a heart that shows emotion. And only the Phoenix monarch can control it as the sun becomes his/her heart. The Moon is controlled by anyone with Moonelisa. Formerly, Prince Arte is in control of the Moon. Now that Arte is banished there is no moon.
The monarch and the Sun are apart of each other. So if the monarch feels a certain way than the Sun will shine a certain way.
- If angry → heats → makes a hot day
- If happy → shine makes a bright day
- If shy, unhappy, or scared → cloudy → makes the sky cloudy covering the sun
- If sad → stormy → rains
- If sleepy → sunset → nighttime
- If calm → shimmer → makes a warm day
- If evil → eclipse → no visible sun
Any other emotions will not effect the sun.