02 The Solar System

Question 1

To what degree is the Earth tilted in relation to the Sun?

Answer 1

23.5 degrees

Question 2

What is the ‘Equinox’ and when are they?

Answer 2

• Points in the Earths orbit where the day and night is equal in both hemispheres
• Spring Equinox: 21st Mar
• Autumn Equinox: 21st Sep

Question 3

What are the ‘Solstice’ and when are they?

Answer 3

• Solstice is the points on the Earths orbit of the Sun with the longest day and longest night
• Summer Solstice: 21st Jun (longest day)
• Winter Solstice: 21st Dec (longest night)

Question 4

At what latitude are the following?

• Tropic of Cancer
• Tropic of Capricorn
• Artic Circle
• Antarctic Circle

Answer 4

• Tropic of Cancer: 23.5 degrees North
• Tropic of Capricorn: 23.5 degrees South
• Artic Circle: 66 degrees North
• Antarctic Circle: 66 degrees South

Question 5

What are the points in the Earths orbit where the Earth is closest and furthest from the Sun called and when do they occur?

Answer 5

• Perihelion (closest): 3rd Jan

- Aphelion (furthest): 3rd Jul

Question 6

What are Kepler’s two laws?

Answer 6

1. The orbit of a celestial body is elliptical with the Sun at one of the foci
2. The line joining the Sun and a planet, known as the Radius Vector’ sweeps out equal area in an equal time frame

Question 7

What are the rules associated with Leap Years?

Answer 7

• Every 4 years where the year is devisable by 4
• 3 are excluded every 400 years
• I.e. If a century is divisible by 400 then its a leap year

Question 8

Give the name for the Latitude and Longitude used on the Celestial Sphere

Answer 8

• Latitude: Declination

- Longitude: Hour Angle

Question 9

Describe what the ‘Obliquity of the Ecliptic’ is

Answer 9

The angle between the equator and the ecliptic

Question 10

Describe what the Ecliptic is

Answer 10

The Ecliptic is the great circle on the celestial sphere which represents the path of the Sun

Question 11

What position in its orbit is the Earth around the Sun when the greatest and smallest change in day light between days is observed?

Answer 11

• Greatest change is found at the Equinoxes

- Smallest change is found at the Solstices

Question 12

Name the two types of Year and which one is used in today’s calendar?

Answer 12

• Sidereal Year

- Tropical Year (currently used)

Question 13

Name and describe the three types of ‘Day’.

Answer 13

• Sidereal Day: Time between two crossings of the Sun over a particular meridian and a fixed point in space
• Apparent Day: Time between two crossings of the Apparent Sun over a particular meridian and a fixed point in space
• Mean Solar Day: Average Apparent Day (24 hours)

Question 14

In what two months is there the biggest difference between the Mean Sun and the Apparent Sun?

Answer 14

Feb (later than midday) and Nov (Earlier than midday)

Question 15

What is the definition of:

• Declination
• Hour Angle

Answer 15

• Celestial Latitude

- Celestial Longitude

Question 16

Why does the length of the Sidereal day not equal the length of the apparent solar day?

Answer 16

• This is due to the relative motion of the Earth and the Sun
• The Earth orbits the Sun and rotates in the same direction
• This is referred to as a Prograde planet

Question 17

What path does the Mean Sun follow on the celestial sphere?

Answer 17

It follows the celestial equator

Question 18

Regarding Civil Twilight, when is this measured to and from?

Answer 18

Morning and Evening Civil Twilight are measure from where the centre of the Sun is 6 degree below the local horizon