Correct pinyin and pronunciation for 太阳
太阳 Tàiyáng, Sun: pronounced "Tie Yang"


太 Tài：highest; greatest

阳　yáng：sun

You may find some reference yáng as 5th tone (轻声 qīngshēng) because it's easier to pronounce in spoken Chinese. The character 阳 yáng by itself is always 2nd tone.