天の川 (hiragana あまのがわ, romaji Amanogawa, alternative reading あまのかわ, romaji Amanokawa)
The reading Amanogawa is used more commonly than Amanokawa.
From 天 (ama, "heaven," "sky") + の (no, particle forming the genitive case) + 川 (kawa, "river," "stream," "brook")