A spaceship takes off from Earth. An astronomer on Earth can look though a window in the ship's hull and view a clock on the inside. He notes (I assume) it's indicating that time is flowing more slowly inside the ship than on Earth. The astronaut in the ship, however, also has a telescope and can view the clock inside the astronomer's observatory. Since (from his perspective) the spaceship is stationary and the Earth is moving away from it, he notes that the time on the terrestrial clock is flowing more slowly than it is on his ship. This seems like a paradox, though, since the astronomer should age faster than the astronaut. What am I missing? Thanks.