How were Uranus and Neptune discovered?

Question

It is said that the people of the ancient times knew only planets upto Saturn. Uranus and Neptune were the planets discovered in the modern times. How did that happen?

Answer 1

Uranus was discovered quite by accident. Neptune was discovered based on Newton's Law - in fact, credit for Neptune's discovery goes to a Mathematician!

Once Uranus was discovered, astronomers watched its orbit very closely. They noticed there were some wobbles in its orbit. Some of the wobbles could be explained by the gravitational pull of Jupiter and Saturn, but not all of them. Scientists were left with two possibilities - the laws of physics work differently that far out in the Solar System, or there was another planet (as yet undiscovered) causing the wobbles. Since no one wanted to believe that the laws of physics would be any different in different parts of the Solar System, they explored the second possibility. Mathematicians worked out the details of where this new planet would have to be to explain the wobbles, and within 30 minutes (!!!) of looking, Neptune was found.

Answer 2

The above answers are correct. Just to expand on them,
Herschel was systematically searching the sky with his telescope, looking for and cataloging anything that had not been seen before, when he came across Uranus.

Later, it was noticed that Uranus was not moving exactly as calculations predicted it should, so mathematical calculations were done that showed there must be gravity from another large undiscovered planet, and where that planet would have to be to cause the observed discrepancy. When astronomers looked at that part of the sky, there was the planet Neptune.

Answer 3

Uranus was discovered by William Herschel, an English astronomer in March 1781 using a home-made telescope.

Neptune was discovered on September 23, 1846 by Johann Gottfried Galle, of the Berlin Observatory, and Louis d'Arrest, an astronomy student, through mathematical predictions made by Urbain Jean Joseph Le Verrier.

Le Verrier performed calculations to explain discrepancies between Uranus's observed orbit and that predicted from the laws of Kepler and Newton. At the same time, but unknown to each other, the same calculations were made by Adams. Le Verrier assisted Galle in locating the planet (September 1846); which was found within 1° of its predicted location at a point in Aquarius.