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Discovering planets
The discoveries of Ceres,
Uranus, Neptune and Pluto
and the techniques involved
Below are key people, locations and other information about the discoveries of Ceres,
Uranus, Neptune and Pluto. Research these discoveries, and write 4 paragraphs, using
each of the terms below in the paragraphs.
(Press Enter for hints)
1781
Urbain Le Verrier
1801
Uranus
1846
William Herschel
1930
Astronomer Royal
‘star' appeared as a small disk
Pluto
Bath
Berlin Observatory
perturbations
Palermo Observatory
Ceres
own telescope
Clyde Tombaugh
George Airy
Guiseppe Piazza
Johann Galle
Neptune
mistaken for a comet
Lowell Observatory
John Couch Adams
Below are key people, locations and other information about the discoveries of Ceres,
Uranus, Neptune and Pluto. Research these discoveries, and write 4 paragraphs, using
each of the terms below in the paragraphs.
(Press Enter for hints)
Here are some examples…
Uranus was discovered in 1781, when William Herschel was using his own telescope
in his garden at his home in Bath. One ‘star’ appeared as a small disk and was initially
mistaken for a comet. However, subsequent observations showed it was a new planet.
Ceres was discovered in 1801. When Guiseppe Piazza was observing at Palermo
Observatory, he noticed that one faint star changed positions over some days.
Neptune was discovered in 1846. The previous year in England, John Couch Adams
had assumed that perturbations (irregularities) in Uranus’s position might be caused by
an unknown planet and used maths to predict its position. He informed the Astronomer
Royal George Airy, who did nothing with Adam’s work. The following year in France,
Urbain Le Verrier also predicted this new planet, and Johann Galle at Berlin Observatory
searched and found the new planet.
Pluto was discovered in 1930 by Clyde Tombaugh. Using the telescopes at the Lowell
Observatory over a period of time, he eventually located it photographically.
How do astronomers find a ‘non star’ amidst all the other real stars?
Observation 1
Observation 2
Observation 3
Combining the observations…
When the observations are combined
together, the ‘star’ that seems to move is
actually not a star. It could be planet,
dwarf planet, comet or something similar.
By the nineteenth century, astronomers were confident they understood how planets
moved and had for some time been able to accurately predict the position of planets.
However, they couldn’t explain why the predicted and actual positions of Uranus varied.
They concluded:
actual
position of
Uranus on
1st date
Either their laws of gravity were
wrong – unlikely are they seemed
to work for all the other planets, or
there was an unknown planet in in
this area of sky…
predicted
position of
Uranus on
1st date
actual
position of
Uranus on
2nd date
actual
position of
Uranus on
3rd date
…which was pulling Uranus away
from its expected position.
predicted
position of
Uranus on
2nd date
predicted
position of
Uranus on
3rd date
Allowing for the
gravitational pull
on Uranus by the
unknown planet
= Sun
John Couch Adams and Urbain
Le Verrier used mathematics to
calculate the approximate
position of Neptune
Predicted
direction of
Uranus
from Earth
= Earth
= Uranus
= unknown planet (Neptune)
Observed
direction of
Uranus
from Earth