1. What are the three features that distinguish the Earth from other planets?
2. Describe the makeup of the Earth’s atmosphere.
show answer
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?
show answer
13,000 km (average)
Flattened slightly at the poles (by 42 km)
4. What is the shape of the Earth?
show answer
An oblate spheroid (a sphere slightly flattened at the poles.)
5. Give six pieces of evidence to suggest the Earth is not flat.
show answer
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.
show answer
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.
show answer
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?
show answer
It is the plane on which the Earth orbits the Sun.
VIDEO
9. What is the definition of an equinox?
show answer
When the sun resides directly above the equator.
This occurs on the 21st March (Spring/VernalEquinox) and the 22/23 September (Autumnal Equinox ).
VIDEO
10. What are the Tropics of Cancer and Capricorn?
show answer
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 ?
show answer
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?
show answer
An imaginary North to South line running directly through the observer’s zenith.
13. Define Longitude.
show answer
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.
show answer
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?
show answer
Floodlights
Commercial
Car parks
Shopping centres
Sports
Domestic
Security
Streetlights
Car parks + shopping centres.
17. What is CfDS?
show answer
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.
show answer
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.
VIDEO
21. What are the benefits of the Earth’s atmosphere
show answer
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?
show answer
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.
show answer
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.
show answer
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?
show answer
They collect light.
They produce a focused image.
26. What are the two fundamental types of telescope?
show answer
Reflector
Curved mirror collects light (and focuses it)
Refractor
Convex lens collects light and focuses.
27. What is the Objective?
show answer
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?
show answer
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.
show answer
Atmosphere
Cloud
Air turbulence
Skyglow
Water vapour content
Geographic location
Access
Utilities
Ground stability
30. What are the advantages of using telescopes in orbit?
show answer
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?
show answer
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?
show answer
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?
show answer
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.
show answer
James A. Van Allen and his team from the university of Iowa.
38. Describe the Van Allen Belts.
show answer
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?
show answer
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.