Astronomers don’t expect to really see some of the things they look for. Instead, they have to reach conclusions from indirect observation to find things like distant planets or dark matter. They have to observe visible objects like stars and see how their views of these objects change as they are affected by the presence of the things they can’t see directly. Changes in light levels or color, properties that can be seen and recorded and measured, can be caused by the gravitational pull of these other, unseen objects as they pull the light source in one direction or another, or as their gravitational pull focuses the light like a lens, revealing sources of light that were otherwise too dim to notice.
Which is to say, you don’t always have to see something directly to know it’s there. You can see how things change around that thing — how they directly respond to its presence — and the thing itself is revealed by these ripples in its environment. And then there it is, no secret at all.
