Ay [T5/T6] - Observing the Solar System

Question 1

What is retrograde motion?

Answer 1

Orbital or rotational movement of an object in the opposite direction to the direction it usually goes

Question 2

Who was Ptolemy and what was his contribution to the model of the solar system?

Answer 2

Suggested…

• earth was off centre
• epicycles orbited the equant

in the geocentric model

Question 3

Who was Nicolas Copernicus and what was his contribution to the model of the solar system?

Answer 3

Re-suggested…

• heliocentric model based upon mathematical modelling

Question 4

Who was Tycho Brahe and what was his contribution to the model of the solar system?

Answer 4

• made detailed observations of Mars using a sensitive protector
• died before they could be used

Question 5

Who was Johannes Kepler and what was his contribution to the model of the solar system?

Answer 5

• suggested the orbits of the planets were elliptical rather than circular

Question 6

Who was Galileo Galilei and what was his contribution to the model of the solar system?

Answer 6

• made observations of Jupiter’s moons
• observed phases of Venus
• leading to acceptance of heliocentric model

Question 7

What does the geocentric model suggested by Ptolemy look like?

Answer 7

Geocentrict model

Question 8

What does precession mean?

Answer 8

The relatively slow wobbling of the Earth’s axis, tracing a circular path in the sky.

Question 9

What is the definition of the winter solstice?

Answer 9

The day when the sun lies directly overhead on the tropic of capricorn.

Question 10

How long is one axial precession?

Answer 10

25,771.5 years

Question 11

What tilt does the earth rotate on?

Answer 11

The earth rotates on a tilt of 23.5°

Question 12

What is an inferior planet?

Answer 12

A planet closer to the Sun than Earth.

Question 13

What is a superior planet?

Answer 13

A planet further away from the Sun than Earth.

Question 14

What is the name of the path that the planets and sun take across the sky?

Answer 14

The zodiacal band

Question 15

Why do the planets appear to sometimes move backwards in the sky?

Answer 15

Due to…

• retrograde motion
• the changing speeds of the planet

Question 16

What does occultation mean?

Answer 16

A transit where one celestial body obscures and covers another and so blocks its light.

Question 17

What does transit mean?

Answer 17

The passing of a celestial body in front of the sun or celestial line.

Question 18

What does opposition mean?

Answer 18

When the earth is in between the sun and a celestial object.

Typically used to describe a superior planet’s position, and is when we are able to observe it from earth the best.

Question 19

What does conjunction mean?

Answer 19

When a planet is in front of or behind the sun as viewed from earth.

When any planet lies on the furthest side of the sun from the earth, it’s in superior conjunction.

When an inferior planet lies in between the sun and the earth, an inferior conjunction takes place.

Question 20

What does elongation mean?

Answer 20

The angle at which we see an inferior planet - only inferior planets will have elongation

Question 21

When is an inferior planet best viewed?

Answer 21

When it’s at a position forming a 90° angle between the sun and the earth.

Question 22

What are the maximum elongation to eastern and western points called?

Answer 22

Greatest Eastern Elongation (GEE)
Greatest Western Elongation (GWE)

Question 23

What is the definition of the summer solstice?

Answer 23

The day when the sun lies directly overhead on the tropic of cancer.

Question 24

What and when are the two extremes of the sun’s positions in the sky?

Answer 24

• summer solstice (june 21st): sun reaches it’s highest point in the sky
• winter solstice (december 21st): sun reaches it’s lowest point in the sky

Question 25

[Past Paper]
What is the name given to the point of zero right ascension on the celestial sphere, defined by the position of the Sun in the sky on the vernal (spring) equinox?

Answer 25

The first point of Aries

Question 26

Why did Tycho Brahe not include Uranus and Neptune in his model?

Answer 26

They hadn’t been discovered yet