In the 17th century,
Johannes Kepler said that the Star of Bethlehem was a nova. He thought that it was caused by planetary conjunctions. (In a planetary conjunction, two or more planets seem to be quite close together in the sky.)
But although Kepler worked out three laws that described the motion of the planets, it took another 150 years to work out the size of the Solar System. Two planets may
appear to be close together due to our viewing angle, yet be hundreds of millions of miles apart.
A nova happens even farther away. It's a type of dead star re-igniting in a thermonuclear explosion. The nearest stars to us (besides the Sun) are some six trillion miles away and not affected by Solar System planets.
