Are the ancient planets all there is?

That time, that place

A musician from Germany who settled in England as an organist and ground his own telescope mirrors at night — sixteen hours at a stretch, his sister Caroline feeding him by hand as he worked.

Caroline recorded and calculated beside him. In time she discovered eight comets of her own.

Why this question

Their work was not hunting for something special. It was a tedious survey: divide the sky into sections and count the stars in each. Comparing counts in different directions, they thought, might reveal the shape of the star system we belong to.

What was found

In March 1781 something that did not look like a star came into view — not a point but a small disc, and over several nights it moved.

At first he took it for a comet. But the computed orbit was not a comet's long ellipse; it was nearly circular. A planet.

No new planet had appeared beyond the five known since antiquity. The solar system doubled in size overnight.

Herschel found something else later. Measuring the temperature of each color of a prism's spectrum, he found the thermometer highest just beyond the red, where nothing was visible at all. Light the eye cannot see.