Combining them, you get 天 (sky) + 文 (patterns) + 学 (study) = 天文学 (astronomy), and adding 家 (expert) gives you 天文学家 (an expert in the study of the sky's patterns)—an astronomer.
In China, the role of the astronomer has a uniquely deep and long-standing cultural significance that goes far beyond simple scientific inquiry. For millennia, Chinese astronomy was inextricably linked to politics, power, and philosophy. The Emperor was considered the “Son of Heaven” (天子, tiānzǐ), and his right to rule—the Mandate of Heaven (天命, tiānmìng)—was believed to be reflected in the skies. Therefore, the ability to accurately predict celestial events like eclipses, track comets, and create the official calendar was not just a scientific pursuit; it was a demonstration of the Emperor's legitimacy and the dynasty's stability. This contrasts sharply with the Western concept of an astronomer, which, especially after the Renaissance, became increasingly separated from state power and religious doctrine, evolving into a more purely academic and research-oriented profession. While a NASA astronomer today serves the state, their discoveries don't determine the legitimacy of the U.S. President. In ancient China, the court 天文学家 was a high-ranking official whose work could have profound political implications. A failed eclipse prediction could be interpreted as a sign that the Emperor was losing favor with the heavens, potentially sparking unrest. Today, the term is purely scientific, but this historical legacy gives the profession a subtle, lingering aura of prestige and profound importance in the Chinese cultural consciousness.
天文学家 is a formal and specific noun. It's used in contexts where precision is needed, such as in education, news reporting, scientific discussions, and when talking about careers.