Topic 2.3 - Solar System Discoveries

Question 1

Who developed the first heliocentric (sun-centred) model of the Universe?

Answer 1

Nicolaus Copernicus

Question 2

What was Nicolaus Copernicus’ first heliocentric model of the Earth made up of?

Answer 2

The Earth, Moon, Sun, 5 planets and fixed stars

Question 3

Who made the idea of a geocentric universe?

Answer 3

The Egyptian philosopher Ptolemy

Question 4

Who published a book explaining retrograde movement?

Answer 4

Nicolaus Copernicus

Question 5

Talk about the laws of planetary motion (who made the observations and who formulated them).

Answer 5

Tycho Brahe was a Danish astronomer who was keen to obtain physical proof that the Earth orbited the sun after Copernicus died. However, unfortunately Tycho died suddenly in 1601 so his assistant Johannes Kepler used observations of Mars that Tycho had made to formulate his laws of planetary movement.

Question 6

What book was the first two laws of planetary movement published in?

Answer 6

Astronomia Nova (new astronomy) in 1609

Question 7

What book was the third law of planetary movement published in?

Answer 7

Harmonies Mundi (harmonies of the world) in 1619

Question 8

What is Kepler’s first law of planetary movement?

Answer 8

Planets move in an elliptical orbit around the Sun with the Sun at the focus of each eclipse

Question 9

What is Kepler’s second law of planetary movement?

Answer 9

This relates to a planet’s speed and its distance to the Sun: ‘An imaginary line from a planet to the Sun sweeps out equal areas in equal intervals of time.’ When a planet is nearer to the Sun it moves faster than the further ones due to its distance from the Sun

Question 10

What is Kepler’s third law of planetary movement?

Answer 10

For GCSE all that’s need to know is a simplified equation relating to the orbital period of a planet around the Sun in years (T) and its mean distance from the Sun in AU (r)

T² = r³

Question 11

Who invented the optick cube (telescope)?

Answer 11

Galileo Galilei

Question 12

Name 3 of Galileo’s other discoveries.

Answer 12

1. The Moon was not spherical but contained ‘hollows and protuberances’ i.e. mountains and craters
2. Venus exhibited phases like the Moon and changed its apparent size on a timescale of weeks
3. Four satellites were in orbit around Jupiter: Callisto, Europa, Ganymede and Io

Question 13

Who was the first scientist to observe the Moon and other astronomical bodies and telescopically and record what he saw?

Answer 13

Thomas Harriot

Question 14

Which of Galileo’s observations gave strong evidence in favour of the heliocentric universe?

Answer 14

Venus’ phases and the moons of Jupiter

Question 15

What did Isaac Newton do?

Answer 15

Used his theory of gravitation to explain planetary orbit. By this time, heliocentric cosmology was universally accepted

Question 16

Explain inverse square law.

Answer 16

The gravitational force of attraction between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. E.g. if the distance between two objects doubles, the force is one quarter of its previous value (one quarter is the inverse of 2 squared)

Question 17

Who by and when was Uranus discovered?

Answer 17

1781 by William Herschel

Question 18

Explain the discovery of Uranus.

Answer 18

William Herschel had been carrying out a ‘review of the heavens’ with a home-made telescope from the garden f his house in Bath, with particular emphasis on faint, naked-eye stars. Herschel four one star that appeared as a small disc. At first he mistook it for a comet, but subsequent observations allowed Herschel to determine an orbit from which he deduced the object to be a new planet

Question 19

Who discovered Ceres and when?

Answer 19

It was the first asteroid to be discovered until its status was changed into a dwarf planet. It was discovered in 1801 by Giuseppe Piazza

Question 20

Explain the discovery of Ceres.

Answer 20

Several astronomers predicted that an undiscovered planet lay in the obvious gas between the orbits of Mars and Jupiter. Around the same time (1800), Piazza was observing the skies at the Palermo Observatory and noted that a faint star had moved position on several successive nights, Piazza announced that he had discovered a new comet but was unable to observe it for much longer as he fell ill. Later in 1801 an orbit was determined by Carl Friedrich Gauss and von Zach was able to confirm the existence of the new ‘planet’

Question 21

How was Neptune discovered?

Answer 21

In 1846 the existence of a planet beyond Uranus was predicted independently by the English undergraduate John Couch Adams and the French Astronomer, to account for ‘wobbles’ or perturbations in the motion of Uranus. Adams predicted an orbit but no search for the planet was carried out and Le Verrier informed the Director of the Berlin Observatory, Johann Encke. 2 of his assistants discovered the new planet on the first night of their telescopic search near Le Verrier’s predicted position

Question 22

What is a perturbation?

Answer 22

The complex motion where a massive body subject to forces other than the gravitational attraction(from sun) is being affected by another massive body

Question 23

How was Pluto discovered?

Answer 23

Uranus was observed to undergo further irregularities in its orbit. American astronomers Edward Pickering and Percival Lowell incorrectly suggested that a second, undiscovered planet might be affecting he motion of Uranus gravitationally. American student Clyde Tombaugh located the planet photographically at the Lowell Observatory in Arizona 1930.

Question 24

How was the idea of a geocentric universe made?

Answer 24

Ptomely used planetary observations made by the Greek astronomer Hipparchus