Sun, Moon, and Stars: Astronomy for Beginners · Part II, Ch. IX · Part 2: Part II: A closer look at the Solar System
22. Uranus and Neptune: a planet found with pencil and paper
Goal: Your child can tell how Herschel found Uranus and how Adams and Leverrier found Neptune by working out where it had to be.
You'll need
- The book, open to Part II, Chapter IX
- A friend or family member to play 'hidden planet'
- A small ball and a long piece of string
What's in the book
Till 1781 Saturn was the outermost planet known. The chapter tells how Herschel found Uranus, and how Uranus kept wandering from its predicted path until two young astronomers, John Couch Adams and Leverrier, each worked out where an unseen planet must be pulling it. Neptune was found close to that very spot.
The lesson, step by step
Read together
Read the chapter aloud. The detective story is the heart of it, so read it with some drama.
Play 'hidden planet'
One person (the hidden planet) stands behind a door or curtain. Another walks slowly past the door with a ball on a long string swinging in front of them. The hidden planet gently tugs the string as the walker passes.
The watcher sees the ball wobble off its straight line and has to guess where the hidden puller is standing. That is what Adams and Leverrier did with Uranus.
A triumph of thinking
Read:
This was indeed a triumph of human intellect.
SayThey found a planet without looking for it first. They used the laws of gravity and arithmetic, then the telescope proved them right.
What we know now
Neptune was first seen in 1846 at the Berlin observatory, using Leverrier's prediction.
Uranus is tipped right over on its side, so each pole has about 42 years of daylight and then 42 years of darkness, even longer and drearier than the book imagined.
Both are 'ice giants' with thick blue-green air. Neptune is a little narrower than Uranus but heavier, and it has the fastest winds in the Solar System.
Only one spacecraft, Voyager 2, has visited them: Uranus in 1986 and Neptune in 1989. Uranus has more than two dozen known moons and Neptune more than a dozen, and both have faint rings.
Tell it back
Ask your child to tell the story of Neptune's discovery as if they were a newspaper reporter in 1846.
Check questions
Who discovered Uranus, and what did he first think it was?
How did astronomers know there must be another planet beyond Uranus?
How long is a year on Uranus?
Afterwards
Add Uranus and Neptune to the planet chart. Your chart now holds all eight planets.
Answers to the book's problems
William Herschel; he first took it for a comet without a tail. Because Uranus did not follow its predicted path, sometimes going faster and sometimes slower; something unseen beyond it had to be pulling on it. About eighty-four of our years.
Worked out for this site from the scan. If a number in your copy differs, trust the book.