Noun
たいようけい
太陽系には惑星はいくつあるんだっけ？
How many planets does the solar system have?
The lineage of the sun (太陽) is that of everything surrounding it. This is the solar system.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. Will help to know 太陽.