Obsessive Astronomer is a uncommon Creature — Human Wizard card from Innistrad: Double Feature (DBL), collector number 152. Current market price: $0.23 (foil $0.45), TCGplayer market prices via Scryfall.
If it's neither day nor night, it becomes day as this creature enters. Whenever day becomes night or night becomes day, discard up to two cards, then draw that many cards.