夜天 is read as やてん (yaten) and means night sky.
やてん
yaten
やまてん
heaven without fighting
よ
dinner
やこう
night train
やかん
night
よなか
middle of the night
よあけ
dawn
よぞら
night sky
やがく
night study
よわ
midnight
やわ
book of informal essays
やしょく
supper
よみち
street at night