Planet Earth Flashcards
What features of the Earth distinguish it from other planets?
70% of the earth’s surface is water.
21% of the earth’s atmosphere is oxygen.
Earth has life in all diverse forms.
What is the composition of the atmosphere?
78% of the atmosphere is nitrogen. 21% of the atmosphere is oxygen. 1% of the atmosphere is argon. 0.04% is carbon dioxide. 0-5% is water vapour. There are traces of neon, helium and methane.
Why is the sky blue?
White light is radiated from the sun to the atmosphere.
Most travels unimpeded.
However, some is scattered preferentially by gas molecules in the atmosphere.
This gives the impression that blue light comes from all directions.
How does the atmosphere change with increasing elevation?
The atmosphere becomes thinner with increasing elevation.
It merges with the space at an altitude of 10,000km.
What is the Kármán Line?
A boundary of 100km that separates the atmosphere from space.
Why does the sky become bluer in the summer?
Heat changes wavelength.
Why do sunsets occur?
The angle of light reaching the observer changes the wavelength of light.
Why is the atmosphere beneficial to humankind?
Absorbs harmful solar ultraviolet radiation, which can cause accelerated skin ageing and cancer.
Absorbs harmful energetic X and Gamma Rays.
Regulates the temperature and prevents extremes - keeps mean at 15 degrees. Allows water to exist in its liquid form.
Oxygen enables respiration.
Burns up meteoroids due to friction. Means that they do not reach the ground in most cases.
List some major causes of light pollution.
The moon.
Urban streetlamps and motorway lights.
Domestic and industrial security lamps.
Lights above car parks and shopping centres.
Why is light pollution undesirable to astronomers?
Creates background yellow haze.
Reduces contrast and means that dimmer objects cannot be seen.
Disrupts night vision.
How do you tackle light pollution?
Make better designed lighting.
Direct lighting to the ground.
Persuade local authorities to tackle the issue and join the British Astronomical Association’s Campaign for Dark Skies.
How do you find the circumference of the earth?
Find the difference in angle of a stick’s shadow…
At two different locations.
Find the distance between these locations.
Extrapolate the distance to complete the circle.
Who was Eratosthenes?
A Greek mathematician and geographer.
Around the 3rd century BC.
How did Eratosthenes make the first accurate calculation of the circumference of the earth?
Found the angle using sticks of the shadow at two different locations (Alexandria and Syene - where Syene was on the Tropic of Cancer).
Found the difference in these angles to be 7 degrees.
Found the distance between these two locations to be 790km.
Multiplied this distance by 50 to get the circumference of the whole earth.
Found the value to be 40,000km.
Why are there several problems with Eratosthenes’ method?
Not apparent how he knew the distance between Alexandria and Syene.
Difficult to convert the units of distance he used (stadia) unto km.
Syene was not quite on the Tropic of Cancer.
What is the shape of the earth?
Oblate spheroid.
What is the diameter of the earth?
13,000km.
By how many km is the earth flattened at the poles?
43km.
What evidence is there that the earth is spherical?
Ships disappear over the horizon.
Satellites orbit the earth.
Images of the earth from space.
During a lunar eclipse, the earth’s shadow has a curved shape.
Aircraft travel in arcs rather than straight lines - the shortest distance on a curved surface.
What is the rotation period of the earth (also known as a sidereal day)?
23 hours 56 minutes.
How many minutes does the earth take to rotate 1 degree?
4 minutes.
What is a sidereal day?
The rotation period of the earth relative to the movement of other stars.
What is the equator?
The imaginary lines equidistant from the two poles.
What are the tropics?
The areas between the lines + and - 23.5 degrees.
What is latitude?
The angle from where you are, to the centre of the earth, to the point on the equator which intersects your meridian.
What is longitude?
The angle east or west between the two meridians.
What is the pole?
The imaginary line that passes through the top and bottom of the earth so that the Earth rotates around this axis.
What is the horizon?
The astronomical horizon is the tangent to the earth’s surface. The true horizon is where the earth meets the sky.
What is the meridian?
The meridian is the imaginary line running north and south overhead, through your zenith.
What is the prime meridian?
The prime meridian is the north south line that passes through Greenwich, London.
What is your zenith?
The point in the sky directly above you.
What is the spring equinox?
Date: 21st March
Involves the equator.
What is the summer solstice?
Date: June 21st
Involves the Tropic of Cancer.
What is the autumnal equinox?
Date: 21st September
Involves the equator.
What is the winter solstice?
Date: 21st December
involves the Tropic of Capricorn.
What are the drawbacks of the earth’s atmosphere?
Because all frequencies are absorbed to a certain extent, light is dimmer.
Preferential scattering of blue light limits observations to night.
Weather and clouds scatter light.
Most radiation does not reach the ground.
There are scintillations due to the turbulence of the atmosphere, which reduces resolution and causes stars to twinkle.
Why are optical and infra-red observatories sited in high mountains or in space?
On higher mountains, there is less atmosphere.
In space, frequencies other than light can be observed.
Does a reflector or a refractor use a curved mirror?
Reflecting
Does a reflector or a refactor use a glass convex lens?
Refracting
Draw a diagram of a reflecting telescope.
Check notes
Draw a diagram of a refracting telescope.
Check notes
Why are large telescopes advantageous?
They collect more light in proportion to their diameter. They therefore have a shorter observing time.
They also have higher resolution.
What is adaptive optics?
Used to compensate for:
Imperfections in mirrors which affect light.
Turbulence of the atmosphere.
What is the objective of a telescope?
Its lens.
What is the size of a telescope?
Diameter.
Why are the world’s largest telescopes reflectors?
Large mirrors are easier to transport, cheaper and lighter than lenses.
Mirrors can be engineered to a higher precision.
Reflectors have no chromatic aberration.
Adaptive optics can only be used in reflectors.
What happens to radio waves in the earth’s atmosphere?
Longer radio waves are reflected by ions in the ionosphere.
Shorter wavelength radio waves can enter the atmosphere.
What happens to microwaves in the earth’s atmosphere?
Longer wavelength microwaves can enter the atmosphere.
Shorter wavelength microwaves are absorbed by water vapour and oxygen.
What happens to infrared in the earth’s atmosphere?
Absorbed by water vapour, carbon dioxide and methane at longer wavelengths.
What happens to UV in the earth’s atmosphere?
Absorbed by ozone and oxygen at shorter wavelengths.
What happens to X rays in the earth’s atmosphere?
Absorbed by oxygen and nitrogen; ionise atoms and molecules.
What happens to gamma rays in the earth’s atmosphere?
Absorbed by oxygen and nitrogen, excite nuclei.
List some atmospheric properties of a site for a telescope.
Cloud cover Water vapour content Sky brightness Air turbulence Thermal / background noise
List some geographic properties of a site for a telescope.
Access
Utilities
Ground stability
Likelihood of earthquakes
What are the advantages of space telescopes?
- No atmosphere to blur images/reduce resolution
- No light pollution because sky is dark
- Can observe other wavelengths
- No adverse weather problems
- No preferential scattering of blue light - observations not limited to day
What are the disadvantages of Space Telescopes?
- Reduced lifetime
- Hard to maintain and repair
- Expensive to build and launch
When was the James Webb telescope launched?
2013
What is the length in m of its primary mirror?
6.5m
What does the James Webb telescope measure?
Infra-red light
How do you prevent the James Webb telescope from overheating and interfering with its own infra-red observations?
- Cryogenic cooling systems - ‘open’ design
2. Unusual orbit uses Earth to shield itself from Sun’s radiation
How was the Inner Belt discovered?
January 1958
By a Geiger counter on Explorer 1
Which was designed originally to study the intensity of cosmic rays from further away
How was the Outer Belt discovered?
December 1958
Geiger counter on Pioneer 3
Pioneer 3’s primary mission was a lunar flyby but run out of floor reaching 100,000km
What is the nature of the Inner Belt?
Compact
High energy protons
Formed by collisions with cosmic rays and atoms in the atmosphere
6000-10,000km above Earth
What is the nature of the Outer Belt?
Diffuse and dynamic, has ‘horns’
Electrons and other charged particles
Formed by emissions from the sun as a result of increased solar activity
15,000-65,000km above Earth
What are the Van Allen Belts?
Two doughnut-shaped rings of high energy particles held in place by Earth’s magnetic field.
