Topic One: Earth, Moon and Sun Flashcards
What are three features that distinguish the Earth from other planets?
Atmosphere
Water
Life
Describe the makeup of Earth’s atmosphere:
Nitrogen 78%
Oxygen 21%
Argon 1%
Carbon Dioxide 0.04%
What is the diameter of the Earth?
roughly 13,000km
What is the shape of the Earth?
Oblate Spheroid
Give six pieces of evidence to suggest the Earth is not flat:
- Ships disappear below the horizon
- Satellites orbit the Earth
- The curvature of the Earth’s shadow during a partial lunar eclipse
- Aircraft fly in arcs rather than in straight lines
- 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 Latitude
The angle between a point on the Earth’s surface, the centre of the Earth and the equator. Expressed as an angle in North of South of the equator
Describe the Earth’s polar axis:
Titled by 66.5 degrees to the plane of the ecliptic
What is the Ecliptic?
It is the plane on which the Earth orbits the sun
Define equinox
When the sun resides directly above the equator
When is the spring equinox?
21st March
When is the autumnal equinox?
22nd/23rd September
What is a Solstice?
When the sun resides directly over the Tropic of Cancer (21st June) or the Tropic of Capricorn (21st December)
What is a Meridian?
An imaginary North to South line running directly through the observers zenith
Define Longitude
The angular displacement east or west of the Prime Meridian
Define Zenith
A point directly above the observer
Define Horizon
The imaginary line along which the sky meets the sea/land
What are the main causes of skyglow?
Floodlights
Streetlights
Car parks + shopping centres
What did Eratosthenes do?
Measured Earth’s circumfrence
When did Eratosthenes measure the Earth’s circumference?
3rd Century BC
How did Eratosthenes measure the Earth’s circumference?
He read that at noon on the Summer Solstice, no shadows were casted in Syrene
At the same time in Alexandria, the suns position was 7 degrees (one 50th of a circle) from the Zenith
He knew that the distance from Syrene to Alexandria was 790km and used simple geometry to work out the circumfrence of the Earth was 50x this
What are the benefits of Earth’s atmosphere?
Absorbs harmful UV radiation that causes skin cancer
Absorbs harmful gamma and x-rays
Regulates temperature, allowing liquid water
Provides us with oxygen
Protects us from PHOs
What are the drawbacks of the atmosphere for astronomers?
Not all the wavelengths reach Earth so many telescopes have to be placed on satellites
Refraction spikes restrict resolution
Light scattering makes the sky appear blue, meaning astronomers can only observe during the night
What are the “windows” that allow EMR to hit the ground?
Optical Window
Radio Window
Describe the effects of the atmosphere on Electromagnetic Radiation:
Long wavelengths reflected back into space by electrons in the ionosphere
Short wavelengths absorbed
What is Infra-Red radiation absorbed by in the atmosphere?
Carbon Dioxide, water vapour and methane
What is UV radiation absorbed by?
The Ozone
What are X-rays and Gamma Rays absorbed by?
Oxygen and Nitrogen
What are the main functions of a telescope?
They collect light
They produce a focused image
What are the two fundamental types of a telescope?
Reflector - curved mirror collects light and focuses it
Refractor - convex lens collect light and focuses
What is the objective?
The lens or the mirror of a telescope
Name two considerations when choosing an observing site:
Atmosphere (Cloud, Air turbulence, skyglow, water vapour)
Geographic location (Access, utilities, ground stability)
What are the advantages of large telescopes over small telescopes?
Collection of more light
Higher resolution (less diffraction)
Observing times can be shorter
What are the advantages of using telescopes in orbit?
No atmosphere - greater resolution, other wavelengths
No light pollution
What are the disadvantages of using telescopes in orbit?
Difficult to maintain/repair/upgrade - shorter lifetime, radiation damage, solar wind
Expensive
What is the successor to the Hubble Space Telescope?
The James Web Space Telescope
Why do Space telescopes have to be cooled to near absolute 0?
So they won’t generate their own Infra-Red which will affect the results
What is the size of the objective on the JWST?
6.5m
When will the JWST launch?
2016
How will the JWST reduce the amount of coolant needed?
Open design so it doesn’t trap hear
Unusual orbit to use the Earth to shield from the Sun
Large sun shield
Who discovered the Van Allen belts?
James A. Van Allen