1.1 : Planet Earth

What key features distinguish the Earth from other planets?
Its atmosphere (mostly oxygen and nitrogen), the existence of liquid water (covering about 70% of the surface) and the presence of life.
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What is the shape of the Earth?
An oblate spheroid -- a sphere (of average diameter 13,000km) flattened by 42km ar the poles.
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What are some examples of proof for the Earth being spherical?
The horizon, satellite orbit and the curvature of the Earth's shadow during a partial lunar eclipse.
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In what way does the Earth rotate?
The Earth rotates around its axis that passes through the North and South geographic poles (the magnetic poles are slightly displaced from these).
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The equator divides the Earth into...
The northern and southern hemispheres.
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What are lines of latitude and longitude?
Parallel horizontal and vertical lines running along the Earth's surface that provide reference for identifying points on the Earth's surface.
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What is the latitude of a point on the Earth's surface?
The angle between that point, the Earth's centre and a point on the equator, expressed as an angle north or south of the equator.
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What are the latitudes of the poles?
The North Pole has a latitude of 90°N and the South Pole has a latitude of 90°S.
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How much is the Earth's polar axis tilted to the ecliptic (the plane on which it orbits the Sun)?
It is tilted by 66.5°.
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What is an equinox and how often do they occur?
An equinox is the point at which the Sun lies directly over the equator. This occurs on two dates a year: the spring equinox (21st March) and the autumnal equinox (22nd/23rd September).
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What is the maximum degree to which the Sun can be displaced from the equator between the equinoxes?
23.5°.
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What are the latitudes of the tropics?
The Tropic of Cancer has a latitude of 23.5°N and the Tropic of Capricorn has a latitude of 23.5°S.
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What is a solstice?
The dates on which the Sun lies above one of the tropics. The Sun lies above the Tropic of Cancer on the summer solstice (21st June) and the Tropic of Capricorn on the winter solstice (21st December).
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What is the observer's meridian?
A north-south line running through the point at which the observer stands.
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What is the longitude of a point on the Earth's surface?
The angular displacement of the observer's meridian from the Prime Meridian (passing through Greenwich, London), expressed as an angle east or west of the Prime Meridian.
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What is the observer's zenith?
A line running north-south on the sky, passing directly overhead.
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What is the observer's horizon?
The imaginary plane that meets the observer at a tangent to the Earth's surface.
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What is skyglow?
A form of light pollution that can hinder observations of the night sky by producing an orange haze in the sky.
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What are the main sources of terrestrial light pollution?
Commercial and sports floodlights; urban streetlamps and motorway lights; domestic and industrial security lights; and lights above car parks and shopping centres.
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How did Eratosthenes determine the Earth's circumference?
By using simple geometry with the distance between Syene and Alexandria (790km) and the Sun's displacement from the zenith position at noon in Alexandria (7°).
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What are some flaws in Eratosthenes' method?
Syene's slight displacement from the Tropic of Cancer, the uncertainty in the distance from Syene to Alexandria and the conversion of the unit used to measure the distance to km.
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What are the main constituents of the Earth's atmosphere?
Nitrogen (78%), oxygen (21%), argon (1%), carbon dioxide (0.04%), water vapour (variable -- averages at 1%) and traces of neon, helium and methane.
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The atmosphere becomes gradually thinner...
With increasing distance from Earth.
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What is the Kármán line?
The most commonly accepted boundary between the top of the atmosphere and space, at an altitude of 100km.
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What are some advantages of the Earth's atmosphere?
It absorbs carcinogenic UV rays, X-rays and gamma rays, regulates the Earth's temperature (allowing the existence of liquid water), provides us with oxygen and partly protects us from meteoroids (they burn up as they pass through).
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What is the average surface temperature of Earth?
15°C.
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What are some disadvantages of the Earth's atmosphere?
It refracts starlight, causes the sky to appear blue (due to gas molecules causing the selective scattering of the shorter wavelengths of sunlight) and absorbs and reflects the majority of EM radiation from space, all of which hinders observations.
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What are the two 'main' windows through which radiation from space can reach the ground?
The optical window (which allows visible light) and the radio window (which allows some waves in the microwave/radio region).
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How does the atmosphere effect radio waves, microwaves and IR radiation?
The longest radio waves are reflected back into space by electrons in the ionosphere; some shorter microwaves are absorbed by oxygen and water vapour; most IR radiation is absorbed by water vapour, carbon dioxide and methane.
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How does the atmosphere effect UV radiation, X-rays and gamma rays?
UV radiation is absorbed by ozone and, at shorter wavelengths, oxygen; X-rays and gamma rays are absorbed by oxygen and nitrogen (X-rays ionise atoms and molecules while gamma rays excite their nuclei).
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What is a refractor telescope?
A telescope with a glass convex lens that collects the light and brings it to a focus.
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What is a reflector telescope?
A telescope with a curved mirror that collects the light.
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What is a telescope's objective?
Its lens or mirror.
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What are the two main advantages of larger telescopes?
They collect more light in proportion to area and provides a higher resolution (level of image detail) in proportion to diameter.
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Why are most professional telescopes reflectors?
Mirrors are much lighter than lenses and can be manufactured to a much higher precision.
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What factors must be considered for an ideal observing site?
Atmospheric properties (cloud cover, air turbulence, sky brightness, water vapour content) and geographic location (access, utilities, ground stability, likelihood of earthquakes).
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What are some advantages of space telescopes?
They have longer observing periods and the ability to detect other radiation and are not effected by an atmosphere, light pollution or adverse weather problems.
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What are some disadvantages of space telescopes?
They have a reduced lifetime, are difficult to maintain and are much more expensive.
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What are the Van Allen Belts?
Two doughnut-shaped rings of spiraling high-energy particles held in place high above the Earth's equatorial region by the Earth's magnetic field.
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Describe the inner Van Allen Belt.
The compact inner belt consists of mainly high-energy protons, formed by collisions between cosmic rays and atoms in the atmosphere. It has a relatively low altitude (0.1 - 1.5 Earth radii), causing problems for astronauts (radiation exposure).
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Describe the outer Van Allen Belt.
The diffuse outer belt consists mainly of electrons and other charged particles emitted by the Sun during periods of increased solar activity. It has an altitude between 3 and 10 Earth radii.
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How was the inner belt discovered?
Using a Geiger counter aboard Explorer 1, the first successful US satellite.
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How was the outer belt discovered?
Using instruments aboard the US probe Pioneer 3.
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Other cards in this set

Card 2

Front

What is the shape of the Earth?

Back

An oblate spheroid -- a sphere (of average diameter 13,000km) flattened by 42km ar the poles.

Card 3

Front

What are some examples of proof for the Earth being spherical?

Back

Preview of the front of card 3

Card 4

Front

In what way does the Earth rotate?

Back

Preview of the front of card 4

Card 5

Front

The equator divides the Earth into...

Back

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