The Earth

Question 1

What are the three features that distinguish the Earth from other planets?

Answer 1

Atmosphere.
Water.
Life.

Question 2

Describe the makeup of the Earth’s atmosphere.

Answer 2

Nitrogen (78%)
Oxygen (21%)
Argon (1%)
Carbon Dioxide (0.04%)
Water vapour (1% average)
Neon, Helium, Methane (trace)

Question 3

What is the diameter of the Earth?

Answer 3

13,000 km (average)
Flattened slightly at the poles (by 42 km)

Question 4

What is the shape of the Earth?

Answer 4

An oblate spheroid (a sphere slightly flattened at the poles.)

Question 5

Give six pieces of evidence to suggest the Earth is not flat.

Answer 5

1. Ships disappear below the horizon.
2. Satellites orbit the earth (impossible if Earth was flat).
3. The curvature of the Earth’s shadow during a partial lunar eclipse.
4. Aircraft fly in arcs rather than straight lines ( because this is the shortest distance on a curved earth).
5. Images of Earth from space.
6. Eratosthenes (because shadows of an object at the same time of day should be the same if earth was flat).

Question 6

Define the term latitude

Answer 6

Lattitude is the angle between a point on the Earth’s surface, the centre of the Earth and the equator. It is expressed as an angle in degree North or South of the Equator.

Question 7

Describe the Earth’s polar axis

Answer 7

Tilted by 66.5o to the plane of the ecliptic
Tilt of the earth’s axis is 23.5o from the perpendicular to the ecliptic.

Question 8

What is the Ecliptic?

Answer 8

It is the plane on which the Earth orbits the Sun.

Question 9

What is the definition of an equinox?

Answer 9

When the sun resides directly above the equator.
This occurs on the 21st March (Spring/VernalEquinox) and the 22/23 September (Autumnal Equinox ).

Question 10

What are the Tropics of Cancer and Capricorn?

Answer 10

Between the equinoxes, the sun resides over different latitudes up to a maximum of 23.5o.
The imaginary circles at these extreme latitudes are called the “Tropic of Cancer” (23.5oN) and the “Tropic of Capricorn” (23.5oS).

Question 11

What is a Solstice ?

Answer 11

When the sun resides directly over the Tropic of Cancer (21st June) or the Tropic of Capricorn ( 21st of December ).

Question 12

What is a Meridian?

Answer 12

An imaginary North to South line running directly through the observer’s zenith.

Question 13

Define Longitude.

Answer 13

The angular displacement East or west of the observer’s meridian from the Prime Meridian (that passes through Greenwich).

Question 14

Define Zenith.

Answer 14

A point directly above the observer.

Question 15

Define Horizon.

Answer 15

The imaginary plane that meets the observer at a tangent to the Earth’s surface.
This can be visualised as an imaginary line along which the sky meets the land/sea.

Question 16

What are the main causes of skyglow?

Answer 16

Floodlights
Streetlights
Car parks + shopping centres.

Question 17

What is CfDS?

Answer 17

The Campaign for Dark Skies
They campaign against lighting that is: excessive, inneficient, irresponsible, poorly designed

Question 18

What did Eratosthenes do?

Answer 18

Measured Earth’s circumference. (3rd Century BC)

Question 19

How did Eratosthenes measured Earth circumference?

Answer 19

He read that at noon on the Summer Solstice, columns of temples did not cast any shadows in Syene (Tropic of Cancer).

At the same time in Alexandria, the Sun’s position was about 7o (one 50th of a circle) from the Zenith.

He knew that the distance from Syene to Alexandria was 790km and used simple Geometry to work out that the circumference of the earth was 50 x this.

He worked this out to be 39,500km. His reading was very accurate as it was in 5% of the actual circumference.

Question 20

What are the benefits of the Earth’s atmosphere?

Answer 20

1. It absorbs harmful ultraviolet radiation that can cause skin cancer.
2. Absorbs harmful x-rays and gamma-rays.
3. Regulates the temperature allowing water to exist in liquid form.
4. Provides us with oxygen.
5. Protects us from PHO’s.

Question 21

What are the drawbacks of the atmosphere for astronomers?

Answer 21

1. Not all of the wavelengths of EMR reach earth so many of our telescopes need to be placed on Earth orbiting satellites.
2. Refraction causes refraction spikes which restricts resolution.
3. The selective scattering of light causes the sky in the day to appear blue (blues bend best).

Question 22

Describe the “windows” through which EMR reaches the ground.

Answer 22

Most EMR fails to pass through the atmosphere. There are two windows of EMR that are able to penetrate through to the ground:

1. Optical window
2. Radio window

Question 23

Describe the effects of the atmosphere on EMR.

Answer 23

1. Long wavelengths reflected back into space by electrons in the ionosphere
2. Short wavelengths absorbed by water and oxygen.
3. Most IR absorbed by carbon dioxide (CO2), water vapour(H2O), and methane (CH4).
4. UV absorbed by O3 (Ozone). Shorter wavelengths absorbed by O2.
5. X- Rays and Gamma Rays are absorbed by oxygen and nitrogen.
   - X- rays Ionise atoms
   - Gamma rays excite their nuclei.

Question 24

What are the main functions of a telescope?

Answer 24

1. They collect light.
2. They produce a focused image.

Question 25

What are the two fundamental types of telescope?

Answer 25

1. Reflector: Curved mirror collects light (and focuses it)
2. Refractor: Convex lens collects light and focuses.

Question 26

What is the Objective of a telescope?

Answer 26

The lens or the mirror is called the objective and the size of a telescope refers to the diameter of the objective.

Question 27

What are the advantages of large telescopes over small telescopes?

Answer 27

1. Collection of more light
2. Higher resolution (less diffraction therefore finer detail)
3. Observing times can be shorter.

Question 28

Name two considerations when choosing an observing site.

Answer 28

1. Atmosphere
   
   1. Cloud
   2. Air turbulence
   3. Skyglow
   4. Water vapour content
2. Geographic location
   
   1. Access
   2. Utilities
   3. Ground stability

Question 29

What are the advantages of using telescopes in orbit?

Answer 29

1. No atmosphere
   
   1. Greater resolution
   2. Other wavelengths (Gamma rays, X-Rays, Far Infra-Red)
2. No light pollution (No weather, Always dark)

Question 30

What are the disadvantages of using Earth orbiting telescopes?

Answer 30

Difficult to maintain/repair/upgrade
Shorter lifetime
Radiation damage
Solar wind
Expensive

Question 31

What is the successor to the Hubble Space Telescope?

Answer 31

The James Web Space Telescope

Question 32

Why do Space telescopes have to be cooled to near absolute 0?

Answer 32

So that they won’t generate their own infra red which will affect the results.

Question 33

What is the size of the objective on the JWST

Answer 33

When will the JWST launch?

Question 34

How will the JWST Reduce the amount of coolant needed?

Answer 34

1. It will have an open design instead of a conventional tube that could trap heat.
2. An unusual orbit will use the earth to shield it from the sun.
3. It will have a large sun-shield.

Question 35

Who discovered the Van Allen Belts?

Answer 35

James A. Van Allen and his team from the university of Iowa.

Question 36

Describe the Van Allen Belts.

Answer 36

• Inner
  
  • 0.1-1.5 earth radii
  • High energy protons
  • Danger to astronauts and satellites.
• Outer
  
  • 3-10 earth radii
  • High energy electrons
  • Wider belt with “horns” that dip towards the Earth’s magnetic poles.

Question 37

How were the Van Allen Belts discovered?

Answer 37

• Inner belt
  
  • January 1958
  • Geiger counter on Explorer 1.
  • Confirmed by Explorer 3 and Sputnik 3
• Outer Belt
  
  • December 1958
  • Pioneer 3
  • Supposed to be flying to the moon
  • Fell back to earth
  • Its Geiger counter detected the outer belt.