The Earth Flashcards
(37 cards)
What are the three features that distinguish the Earth from other planets?
Atmosphere.
Water.
Life.
Describe the makeup of the Earth’s atmosphere.
Nitrogen (78%)
Oxygen (21%)
Argon (1%)
Carbon Dioxide (0.04%)
Water vapour (1% average)
Neon, Helium, Methane (trace)
What is the diameter of the Earth?
13,000 km (average)
Flattened slightly at the poles (by 42 km)
What is the shape of the Earth?
An oblate spheroid (a sphere slightly flattened at the poles.)
Give six pieces of evidence to suggest the Earth is not flat.
- 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).
Define the term latitude
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 degree North or South of the Equator.
Describe the Earth’s polar axis
Tilted by 66.5o to the plane of the ecliptic
Tilt of the earth’s axis is 23.5o from the perpendicular to the ecliptic.
What is the Ecliptic?
It is the plane on which the Earth orbits the Sun.
What is the definition of an equinox?
When the sun resides directly above the equator.
This occurs on the 21st March (Spring/VernalEquinox) and the 22/23 September (Autumnal Equinox ).
What are the Tropics of Cancer and Capricorn?
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” (23.5oN) and the “Tropic of Capricorn” (23.5oS).
What is a Solstice ?
When the sun resides directly over the Tropic of Cancer (21st June) or the Tropic of Capricorn ( 21st of December ).
What is a Meridian?
An imaginary North to South line running directly through the observer’s zenith.
Define Longitude.
The angular displacement East or west of the observer’s meridian from the Prime Meridian (that passes through Greenwich).
Define Zenith.
A point directly above the observer.
Define Horizon.
The imaginary plane 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.
What are the main causes of skyglow?
Floodlights
Streetlights
Car parks + shopping centres.
What is CfDS?
The Campaign for Dark Skies
They campaign against lighting that is: excessive, inneficient, irresponsible, poorly designed
What did Eratosthenes do?
Measured Earth’s circumference. (3rd Century BC)
How did Eratosthenes measured Earth circumference?
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.
What are the benefits of the Earth’s atmosphere?
- 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.
What are the drawbacks of the atmosphere for astronomers?
- 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).
Describe the “windows” through which EMR reaches the ground.
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
Describe the effects of the atmosphere on EMR.
- 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.
What are the main functions of a telescope?
- They collect light.
- They produce a focused image.
