Topic 1.1 - The Earth Flashcards
What is the Earth’s diameter?
13,000 km
How many degrees is the Earth tilted by?
23 degrees
What shape is the Earth?
Oblate spheroid
How many km is the Earth flattened by?
42 km
What makes up the Earths atmosphere and their percentages?
Nitrogen - 78% Oxygen - 21% Argon - 1% Carbon Dioxide - 0.04% Variable amounts of water vapour - 1% on average Small traces of neon, helium and methane
What is latitude?
How far North or south you are
What is longitude?
How east or west you are
Give 3 pieces of evidence to prove that the Earth is spherical.
- Ships disappear over the horizon
- Satellites orbit the Earth which would be impossible if it was flat
- The curvature of the Earth’s shadow during a partial lunar eclipse
What is an equinox?
When the sun lies directly above the equator. This only happens twice a year
When is the spring equinox?
21st March
When is the autumnal equinox?
22nd/23rd September
What is the zenith?
A point in the sky directly above the observer
What is the meridian?
An imaginary circle passing through the poles at any given point on the Earth’s surface
What is a solstice?
When the sun resides directly of the Tropic of Cancer and the Tropic of Capricorn
When is the summer solstice?
21st June (on the Tropic of Cancer)
When is the winter solstice?
21st December (on the Tropic of Capricorn)
Describe what light pollution is and what it does.
Night observations are sometimes hindered by a form of light pollution called skyglow. A great deal of unwanted and wasteful light shines up into the skies above urban areas at night causing an orange background haze that prevents faint stars, many nebulae and the Milky Way from being observed.
What are the 4 main sources of terrestrial light?
- Commercial and sports floodlights
- Urban street lamps and motorway lights
- Domestic and industrial security lights
- Lights above car parks and shopping centres
Who first determined the circumference of the Earth?
Greek philosopher and mathematician Eratosthenes in the 3rd century BC
Describe the process of Eratosthenes determining the earths circumference.
He read an account that at noon on the date of the summer solstice in Syene on the Tropic of Cancer the sun lay directly over a well. Furthermore, vertical sticks and columns of temples did not cast any shadows at that precise time in Syene. Measurements of the sun’s position at noon in Alexandria on the same date showed that it is just over 7 degrees from the zenith position (this is equivalent to almost exactly 1/50th of a circle). Eratosthenes learnt that Syene was the equivalent of 790km from Alexandria and so he used simple geometry to deduce that the circumference of the Earth was 50 times this value i.e. 39,500km.
Name 6 benefits of the Earths atmosphere.
- It provides us with oxygen so we can breathe
- It allows water to exist in liquid form
- It regulates the Earths temperature
- It absorbs harmful x-rays and gamma rays from space
- It absorbs harmful solar UV radiation that causes skin cancer and accelerated skin ageing
- It partly protects us from meteoroid - the majority burn up as they pass through the atmosphere. Many are visible as meteors or shooting stars
How many degrees North and South are the Tropics of Cancer and Capricorn?
Tropic of Cancer - 23.5°N
Tropic of Capricorn - 23.5°S
Name 3 drawbacks of the Earth’s atmosphere.
- The refraction of light as it passes through our turbulent atmosphere causing stars to ‘twinkle’ and restricting the resolution of an image
- The selective scattering of shorter ‘bluer’ wavelengths of sun by gas molecules in the atmosphere, making the sky appear blue and preventing astronomers from making observations during the day
- The absorption and reflection of the majority of electromagnetic radiation from space, preventing most wavelengths from reaching sea-level and requiring most UV, X-ray and gamma observatories to be placed on Earth-orbiting satellites and not on the ground
What is resolution?
Sharpness, clarity or detail of an image
What is the effect of the atmosphere on the longest radio waves?
They’re reflected back into space by electrons in the ionosphere
What is the effect of the atmosphere on shorter microwaves?
They’re absorbed by water vapour and oxygen
What is the effect of the atmosphere on infra-red radiation?
It’s absorbed by water vapour, carbon dioxide and methane
What is the effect of the atmosphere on UV radiation?
It’s absorbed by ozone and at shorter wavelengths, oxygen
What is the effect of the atmosphere on X-rays and gamma rays?
They’re absorbed by oxygen and nitrogen
What does a telescope do?
It collects light (as much as possible) and produces a focused image that can be viewed, studied, photographed or analysed
What are the two types of telescope?
Refractor and reflector
What does a refractor telescope do?
It is a glass convex lens that collects the light and brings it back to focus
What does a reflector telescope do?
It is a curved mirror (or one made from several segments) that collects light.
What is the lens or mirror of a telescope called?
The objective
What is the size of the telescope referred to as?
Its diameter
Name two advantages that larger telescopes have over smaller telescopes.
- The collection of more light (in proportion to area i.e. the square pf the diameter)
- Higher resolution on proportion to diameter
Name two things that are considered when choosing the ideal observing site.
- Atmospheric properties such as cloud cover, air turbulence, sky brightness and water vapour content
- Geographic location such as access, utilities, likelihood of earthquakes, ground stability
Name 5 advantages of telescopes in orbit over those on the ground.
- No atmosphere to blur images/ reduce resolution
- No light pollution (sky brightness)
- No adverse weather conditions
- Longer observing periods (darkness)
- The ability to detect ‘other’ wavelengths in particular gamma rays, X-rays and far -IR (longer wavelengths)
Name 3 drawbacks of space telescopes.
- Reduced lifetime
- Difficult or impossible maintenance/ repairs/ upgrades
- More expensive to build and launch into orbit
Describe the Van Allen Belts.
Two doughnut shaped rings of spiralling high-energy particles held in place by the Earth’s magnetic field
Who discovered the Van Allen Belts?
James Van Allen
What is the altitude of the outer radiation belts (Van Allen Belts)?
3-10 Earth Radii
What is the altitude of the inner radiation belts (Van Allen Belts).
0.1-1.5 Earth radii
Describe the inner belts (Van Allen Belts).
Mainly high-energy protons formed by collisions between cosmic rays and atoms in the atmosphere
Describe the outer belts (Van Allen Belts).
Mainly of electrons and other charged particles emitted by the sun as a result of increased solar activity
Describe the discovery of the inner Van Allen Belts.
The inner belt was discovered in January 1958 using a Geiger counter on board the first successful US satellite, explorer 1
Describe the discovery of the outer Van Allen Belts.
The outer belt was discovered in December 1958 with the aid of similar instruments to the inner belts carried on the US probe pioneer 3
