1. What are the three features that distinguish the Earth from other planets?
2. Describe the makeup of the Earth’s atmosphere.
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Nitrogen (78%) Oxygen (21%) Argon (1%) Carbon Dioxide (0.04%) Water vapour (1% average) Neon, Helium, Methane (trace)
3. What is the diameter of the Earth?
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13,000 km (average) Flattened slightly at the poles (by 42 km)
4. What is the shape of the Earth?
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An oblate spheroid (a sphere slightly flattened at the poles.)
5. Give six pieces of evidence to suggest the Earth is not flat.
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Ships disappear below the horizon. Satellites orbit the earth (impossible if Earth was flat). The curvature of the Earth’s shadow during a partial lunar eclipse. Aircraft fly in arcs rather than straight lines ( because this is the shortest distance on a curved earth). Images of Earth from space. Eratosthenes (because shadows of an object at the same time of day should be the same if earth was flat).
6. Define the term latitude.
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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 o North or South of the Equator.
7. Describe the Earth’s polar axis.
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Tilted by 66.5 o to the plane of the ecliptic Tilt of the earth’s axis is 23.5 o from the perpendicular to the ecliptic.
8. What is the Ecliptic?
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It is the plane on which the Earth orbits the Sun.
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9. What is the definition of an equinox?
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When the sun resides directly above the equator. This occurs on the 21st March (Spring/VernalEquinox) and the 22/23 September (Autumnal Equinox ).
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10. What are the Tropics of Cancer and Capricorn?
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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” (23.5o N) and the “Tropic of Capricorn” (23.5o S).
11. What is a Solstice ?
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When the sun resides directly over the Tropic of Cancer (21st June) or the Tropic of Capricorn ( 21st of December ).
12. What is a Meridian?
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An imaginary North to South line running directly through the observer’s zenith.
13. Define Longitude.
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The angular displacement East or west of the observer’s meridian from the Prime Meridian (that passes through Greenwich).
14. Define Zenith.
15. Define Horizon.
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The imaginary plain 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.
16. What are the main causes of skyglow?
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Floodlights
Commercial
Car parks Shopping centres
Sports Domestic Security
Streetlights Car parks + shopping centres.
17. What is CfDS?
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The Campaign for Dark Skies They campaign against lighting that is:
o Excessive
o Inefficient
o Irresponsible
o Poorly designed (pointing upwards or unnecessarily bright) .
18. What did Eratosthenes do?
19. When did he do it?
20. Describe how he worked it out.
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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.
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21. What are the benefits of the Earth’s atmosphere
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It absorbs harmful ultraviolet radiation that can cause skin cancer. Absorbs harmful x-rays and gamma-rays. Regulates the temperature allowing water to exist in liquid form. Provides us with oxygen. Protects us from PHO’s.
22. What are the drawbacks of the atmosphere for astronomers?
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Not all of the wavelengths of EMR reach earth so many of our telescopes need to be placed on Earth orbiting satellites. Refraction causes refraction spikes which restricts resolution. The selective scattering of light causes the sky in the day to appear blue (blues bend best).
23. Describe the “windows” through which EMR reaches the ground.
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Most EMR fails to pass through the atmosphere.
There are two windows of EMR that are able to penetrate through to the ground
○ Optical window
○ Radio window
24. Describe the effects of the atmosphere on EMR.
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Long wavelengths reflected back into space by electrons in the ionosphere Short wavelengths absorbed by water and oxygen. Most IR absorbed by carbon dioxide (CO2), water vapour(H2O), and methane (CH4). UV absorbed by O3 (Ozone). Shorter wavelengths absorbed by O2. X- Rays and Gamma Rays are absorbed by oxygen and nitrogen.
X- rays Ionise atoms Gamma rays excite their nuclei.
25. What are the main functions of a telescope?
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They collect light. They produce a focused image.
26. What are the two fundamental types of telescope?
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Reflector
Curved mirror collects light (and focuses it)
Refractor
Convex lens collects light and focuses.
27. What is the Objective?
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The lens or the mirror is called the objective and the size of a telescope refers to the diameter of the objective.
28. What are the advantages of large telescopes over small telescopes?
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Collection of more light
10 m telescope collects 25 x more light than a 2m telescope ( 5 squared)
Higher resolution (less diffraction therefore finer detail) Observing times can be shorter.
29. Name two considerations when choosing an observing site.
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Atmosphere
Cloud Air turbulence Skyglow Water vapour content
Geographic location
Access Utilities Ground stability
30. What are the advantages of using telescopes in orbit?
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No atmosphere
Greater resolution Other wavelengths
Gamma rays X-Rays Far Infra-Red
No light pollution
31. What are the disadvantages of using Earth orbiting telescopes?
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Difficult to maintain/repair/upgrade
Shorter lifetime
Radiation damage Solar wind
Expensive
32. What is the successor to the Hubble Space Telescope
33. Why do Space telescopes have to be cooled to near absolute 0?
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So that they won’t generate their own infra red which will affect the results.
34. What is the size of the objective on the JWST
35. When will the JWST launch?
36. How will the JWST Reduce the amount of coolant needed?
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It will have an open design instead of a conventional tube that could trap heat.
An unusual orbit will use the earth to shield it from the sun.
It will have a large sun-shield.
37. Who discovered the Van Allen Belts.
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James A. Van Allen and his team from the university of Iowa.
38. Describe the Van Allen Belts.
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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.
39. How were the Van Allen Belts discovered?
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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.
