Planet Earth (Earth, Moon and Sun) Flashcards
What is the average diameter of the earth?
13000km
What is the shape of the earth and why?
An oblate spheroid because it is flattened slightly by 42km at the poles.
What evidence is there that the earth is not flat?
Ships disappear over the horizon.
Satellites orbit the Earth- impossible with a flat earth.
The curvature of the earth’s shadow during a partial lunar eclipse.
Aircraft fly in arcs rather than straight lines (because it is the shortest distance on a curved surface)
Images of earth from space.
What are the latitude points for the poles?
90 degrees N and 90 degrees S
By how much is the earth’s polar axis tilted to the plane on which it orbits the sun (ecliptic)?
66.5 degrees
What are the dates for the spring and autumnal equinoxes?
21st March (spring) 22nd/23rd September (Autumn)
What are the imaginary circles at the ‘extreme’ latitudes (23.5 degrees N &
23.5 degrees S)?
Tropic of Cancer (N)
Tropic of Capricorn (S)
What is the observer’s zenith?
Directly overhead the observer
What is an observer’s horizon?
The imaginary plane that meets the observer at a tangent to the Earth’s surface.
What is the word for the form of light pollution that hinders our observations of the night sky?
Skyglow
What are the main sources of terrestrial light pollution?
Commercial and sports floodlights.
Urban street lamps and motorway lights.
Domestic and industrial security lamps.
Lights above car parks and shopping centres.
What year was the British Astronomical Association’s Campaign for Dark Skies (CfDS) set up?
1989
Who was the first person to give an accurate determination of the earth’s circumference?
The Greek geographer and mathematician Eratosthenes in 3rd century BC.
What are three key features that distinguish the earth from all other planets?
Its atmosphere is mainly oxygen and nitrogen
Liquid water (covers 70% of surface)
Life in all diverse forms
How did Eratosthenes find the circumfer
He heard that in Syene now Aswan on the the Summer solstice that the sun lay directly over a well and no shadow was cast from vertical sticks. The measurements of the sun’s position at noon in Alexandria on the same date showed that it was 7 degrees. He measured distance between Syene and Alexandria (790km). Then he did 360/7 and times that by 790 and found 39500km.
What are the main constituents of the atmosphere?
Nitrogen (78%) Oxygen (21%) Argon (1%) Carbon Dioxide (approx 0.04%) Water vapour (1%) Small traces of neon, helium and methane
What is the approx altitude of outer space?
10000km
What is the boundary with a value of 100km called?
The Kármán line
What are the benefits of our atmosphere?
- Absorbs harmful solar ultraviolet radiation that can cause accelerated skin agony and skin cancer, prevents harmful energetic X-Rays and gamma rays reaching the ground by absorbing it.
- Regulates temperature; allows water as liquid and prevents extreme weather.
- Provides us with oxygen to breathe.
- Partly protects us from meteoroids and majority can burn up
What are the problems caused by atmosphere for astronomers?
- The refraction of light as it passes throughout turbulent atmosphere, causing stars to twinkle and restricts resolution of an image.
- The selective scattering of shorter blue wavelengths of sunlight by gas molecules in the atmosphere making sky blue so can’t see in day.
- Absorption and reflection of majority of electromagnetic radiation from space, so some observatories have to be placed in satellites.
What is the order of wavelength sizes shorter to longer?
Gamma, X-ray, Ultraviolet, optical/visible, infrared, microwave, radio
What are the dates of the solstices?
21st June (Summer) 21st December (Winter)
What are the different effects the atmosphere has on radiation?
-The longest radio waves are reflected back into space by electrons in ionosphere.-Some shorter wavelength microwaves absorbed by water vapour and oxygen. -Most infrared radiation is absorbed by water vapour, carbon dioxide and methane. -UV Radiation is absorbed by ozone and at shorter wavelengths by oxygen. -X-rays and gamma rays are absorbed by oxygen and nitrogen.
What are the two types of telescope?
Refractor (glass convex lens collects the light and brings it to focus) and Reflector (in which a curved mirror or one made from several segments collects the light.
In a telescope, what is the lens or mirror and what is the size?
The objective
The size refers to the diameter.
Why are larger telescopes better than smaller ones?
The collection of more light (in proportion to area i.e. The square of the diameter.
Higher (better) resolution (sharpness/amount of detail) in proportional to diameter.
What are ideal observing sites?
Atmospheric properties such as cloud cover, air turbulence, sky brightness, water vapour content.
Geographic location -access, utilities, likelihood of earthquakes, ground stability.
What are advantages of using telescopes in orbit like Hubble or Spitzer to telescopes on ground?
- No Atmosphere to blur images/reduce resolution
- No light pollution (sky brightness)
- No adverse weather problems.
- Longer observing periods (darkness)
- The ability to detect ‘other’ wavelengths, in particular gamma rays, X-rays and far-IR (longer wavelengths)
What are some drawbacks to space telescopes?
- Reduced lifetime
- Difficult or impossible maintenance/repairs/upgrades
- More expensive to build and launch into orbit.
What are Van Allen Belts?
Two doughnut-shaped rings of spiralling high-energy particles held in place by the Earth’s magnetic field. They are found high above the Earth’s equatorial region.
What is the altitude of the compact inner belt consisting mainly of high energy protons formed by collisions between cosmic rays and atoms? (Van Allen Belt)
Between 0.1 and 1.5 Earth radii (about 600km and 10000km).
What is the altitude of the diffuse outer belt consisting mainly of electrons and other charged particles emitted by the sun as a result of increased solar activity? (Van Allen Belt)
Between approx 3 and 10 Earth radii (15000km - 65000km)
By how much is the earth tilt to the equator?
23.5 degrees
