Section 1: Earth, Moon And Sun Flashcards
0
Q
Shape of Earth
A
Oblate spheroid
1
Q
Features of Earth
A
- Atmosphere - mainly oxygen and nitrogen
- Liquid water ~ 70% of surface
- Life
2
Q
Diameter of Earth
A
13000 km
3
Q
Evidence Earth is spherical
A
- Ships disappear over horizon
- Satellites orbit Earth
- Earths shadow curves during partial lunar eclipse
- Images of Earth from space
4
Q
Rotation period of Earth
A
23 hours 56 minutes
5
Q
Time for Earth to rotate 1 degree
A
4 minutes
6
Q
Equator
A
Divides Earth into Northern/Southern hemispheres
7
Q
Tropics
A
Latitude of 23.5 degrees
Cancer = N
Capricorn = S
8
Q
Latitude
A
Parallel to equator
9
Q
Longitude
A
Perpendicular to equator, converge at poles
10
Q
Poles
A
Top and bottom of axis Earth rotates on
11
Q
Meridian
A
Imaginary North-South line running through that point (like longitude)
12
Q
Horizon
A
Tangent to Earths surface from observer
13
Q
Zenith
A
Directly above observer
14
Q
Causes of light pollution
A
- Urban street lamps
- Commercial and sports floodlights
- Domestic and industrial security lamps
15
Q
Problems with light pollution
A
Causes orange background haze which prevents many faint stars, nebulae and the Milky Way from being observed
16
Q
How Eratosthenes calculated Earth’s circumference
A
- On summer solstice Syene on Tropic of Cancer sun lay directly overhead so no shadows were cast
- Same time at Alexandria measurement of sun showed it 7 degrees from zenith = 1/50 of a circle
- Using distance between these places, calculated circumference = 50xdist
17
Q
Make up of Earths atmosphere
A
78% nitrogen; 21% oxygen; 1% argon; 0.04% CO2; 1% water vapour
18
Q
Benefits of Earths atmosphere
A
- Absorbs harmful UV radiation
- Absorbs energetic X/gamma rays
- Regulates temperature
- Provides oxygen to breathe
- Partly protects us from meteoroids
19
Q
Drawbacks of atmosphere
A
- Causes light to refract, restricting resolution of images
- Selective scattering of short blue wavelengths of light causes sky to appear blue so can’t make observations during the day
- Absorption/reflection of most e.m. radiation so UV/X ray observatories etc. must be placed on Earth orbiting satellites
20
Q
Reflecting telescopes
A
A curved mirror collects the light
21
Q
Refracting telescopes
A
Glass convex lens collects the light and brings it to a focus
22
Q
What’s an objective
A
Lens or mirror of telescope
23
Q
Why are large telescopes reflectors
A
Large mirrors can be manufactured to higher precision than lenses and are much lighter
24
Van Allen belts
2 donut shaped rings of high energy particles held in place by Earths magnetic field
25
Inner Van Allen belt
High energy protons from collisions between cosmic rays and atoms in atmosphere
26
Outer Van Allen belt
Electrons and other charged particles emitted by sun during increased solar activity
27
Discovery of Van Allen belts
Inner: Jan 1958 using Geiger counter on board "Explorer 1" satellite
Outer: Dec 1958 similar instruments on board space probe "Pioneer 3"
28
Draw moon map
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Include:
Sea of tranquility
Ocean of Storms
Sea of Crises
Tycho, Copernicus and Kepler craters
Apennines mountain range
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29
Moons diameter
3500 km
30
Moons distance from Earth
380000 km
31
Moons rotational period and orbital period
27.3 days
32
Why is far side of moon not vis. from Earth
Rotational period = orbital period
33
How do astronomers know appearance of far side of moon
Apollo space program to land astronauts on the moon
34
Appearance of far side of moon
Devoid of seas
Entirely mountainous
Heavily cratered
35
Appearance of near side of moon
Dark grey "seas"
Lighter grey mountainous highlands (older)
Rilles - trenches caused by lava flows
Wrinkle ridges - buckling from cooling lava contracting
36
Formation of moon
Giant Impact Hypothesis
Relatively young Earth struck by Theia (Mars-sized)
During impact Theia and Earth's outer layers merged and debris was thrown into Earths orbit = moon
37
Evidence for giant impact hypothesis
1. Relative abundances of isotopes of oxygen same as on Earth
2. Lack of water suggests vaporisation during collision
3. KREEP rocks suggests ocean of hot cooling magma would have surrounded the moon
38
Why doesn't moon have atmosphere
Gravity too low
39
ALSEPs
Apollo space programme and its experimental packages
(1. Laser ranging retroreflector to determine earth moon distance)
2. Structure of moons interior
3. Composition and pressure of lunar atmosphere
4. Presence of micrometeorites ejected by meteorite impacts
40
Purpose of Apollo space program
Collection of lunar soil and rock for analysis
Deployment of scientific experiments on moons surface
Winning space race against Soviet Union to land a human on the moon
41
Sun's diameter
1.4 million km
42
Suns distance from Earth
150 million km
43
Temperature of suns photosphere
5800K
44
Temperature of suns corona
2 million K
45
Observing sun safely
Telescope with H alpha filter
| Indirect projection to reduce brightness
46
Suns rotation period
25 days at equator
| 36 days at pole
47
Sunspots and structure
Cooler areas of photosphere corresponding to strong localised magnetic fields
Umbra - central darker region 2000K cooler than photosphere
Penumbra - lighter surrounding area 200K cooler than photosphere
48
How can astronomers use sunspots to determine suns rotation period
By following apparent motion of sunspots across disc can deduce that sun does not rotate as a solid body
49
Butterfly diagram
Latitude/time chart for sunspots
50
Solar wind
Steady stream of charged particles from suns corona
Slow solar wind - high temp of corona gives particles enough k.e. to escape suns gravity 400km/s
Fast solar wind - coronal holes (open mag. field lines) allow particles to escape at 850km/s
51
Chromosphere
2000km thick
| Reddish pink ring before totality in solar eclipse
52
Corona
Region of ionised gas
| 2 million K
53
Why do sun and moon appear same size in sky
Sun 400x larger but also 400x further away so appears 400x smaller i.e. equal to size of moon
54
Period of lunar phase cycle
29.5 days
55
Describe lunar cycle
New moon
Waxes -> crescent; gibbous; full moon
Wanes -> gibbous; decrescent; new moon
56
Total solar eclipse appearance
Light from suns photosphere obscured
Dark umbra shadow cast on Earth
Sky darkens so some brighter stars can be seen
Suns corona is visible
Baily's beads - suns rays shine through valleys on the moon
57
Partial solar eclipse appearance
Sun appears to have circular bite missing from it
| Earth is cast in penumbra shadow
58
Total lunar eclipse
Moon appears red/copper as light from sun passes through Earths atmosphere and blue light is scattered
59
Partial lunar eclipse
Curved shadow of Earth can be seen on full moon
60
Duration and phase of moon in solar eclipse
Few minutes
| New moon
61
Duration and phase of moon in lunar eclipse
30 mins - 1 hour
| Full moon
62
Why are eclipses rare
Moons orbit tilted slightly to ecliptic so sometimes appears above or below sun in the sky
63
Solar day
24 hours
| Time taken for successive crossings of the sun across the observers meridian
64
Sidereal day
23 h 56 min
| Time taken for successive crossings of a given star across an observers meridian
65
Why are sidereal and solar days different lengths
During 1 complete Earth rotation it has also moved in its orbit around the sun so an extra 4 minutes must be allowed for the sun to return to the same position in the sky
66
Determining time using sundial
Sundial measures apparent solar time but a clock reads mean solar time/GMT
Take into account longitude and EOT to determine GMT from sundial
67
EOT
Apparent solar time - mean solar time
68
Cause of aurorae
Electrons from solar wind accelerated to high speeds in Earth's magnetic field, exciting molecules of oxygen and nitrogen which give out light at characteristic wavelengths
69
Appearance of aurorae and where they can be observed
Green yellow and red whirlpools of light in the sky
| Observed from high latitudes
