Astronomer in 1543: Copernicus moves the Earth · 443

Do you need a PhD to be an astronomer? For research posts, effectively yes: no country licenses astronomers, but universities, observatories and space agencies treat the doctorate as the entry credential, and telescope-time and grant eligibility mostly assume it. People do work in astronomy without one — as telescope operators, instrument engineers, software developers and outreach staff — and amateurs still make real discoveries, but leading research is a PhD's game.

How long does it take to become an astronomer? Roughly nine to twelve years from leaving school to a first independent research position: a three- or four-year bachelor's in physics or astronomy, often a master's in Europe, then a PhD of three to six years. A permanent job usually takes longer still — most astronomers pass through several multi-year postdoctoral contracts, commonly landing a lasting post in their mid-to-late thirties.

What is the difference between an astronomer and an astrophysicist? Today, almost nothing: the titles are used interchangeably on job advertisements and department doors. Historically, astronomy meant measuring positions and motions, while astrophysics — born with spectroscopy in the mid-1800s — meant explaining the physics behind them. Since essentially all modern astronomers work with physics, "astrophysicist" is simply the newer word; "astronomer" is the older and broader one.