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
Describe the Van Allen Belts:
Inner:
0.1-1.5 earth radii
High energy protons
Danger to astronauts and satellites
Outer:
3-10 earth radii
high energy electrons
wider belt with ‘horns’ that dip towards the Earth’s magnetic poles
What is the diameter of the Moon?
3500km
What is the average distance to the moon?
380,000km
What is the strength of Moon’s Gravity?
1/6 G
Why do we only see one side of the moon?
Because the Moon’s orbital period is equal to it’s rotational period
What is the Moon’s rotational period?
27.3 days
What is the Moon’s orbital period?
27.3 days
What is the difference between the Moon’s orbital and rotational period?
Trick question, they are the same.
I tried to be funny, I’m not funny, revision has got me this bored ugh.
I need friends.
What is the Lunar Cycle?
It is the time taken for the Moon to go through a cycle of phases in the sky when observed from Earth
A lunar month is 29.5 days
Why is the Lunar Month 2.2 days longer than the Moon’s orbital period?
An extra 2.2 days is needed to bring the Moon, the Sun and Earth back into alignment.
How and when did we first see the far side of the moon?
Russian Luna 3
October 1959
Dual lens camera
Who were the first humans to see the far side of the moon directly?
Apollo 8 astronauts in December 1968
Describe the lunar landscape (lunar seas):
Lunar seas:
- Maria
- Iron rich basaltic rock
- Dark grey
- Smooth
Describe the lunar landscape (Highlands):
Highlands:
- Terrae
- Anorthosite
- Course grained igneous rock - Lighter grey
- Heavily cratered
Describe the lunar landscape (Notable Features):
Notable Features:
- Sea of Crises
- Apennine Mountains
- Sea of Tranquillity
- Tycho Crater
- Kepler Crater
- Coppernicus crater
- Ocean of Storms
Describe the lunar landscape (Rilles):
Rilles:
- Narrow channel like depressions
- Caused by lava flows
Describe the lunar landscape (Wrinkle ridges):
Wrinkle ridges:
- Ridges up to 100s of km long
- Caused by compressive forces within cooling lava
Why do we think the highland regions are older than the Lunar seas?
Smaller number of craters in the Lunar seas
What were the objectives of NASA’s Apollo Programme?
To put men on the moon
To collect lunar soil and rock for analysis
To perform scientific experiments
To beat the Russians
What went wrong with Apollo 1?
Launch Pad fire:
- welded door shut
- 3 astronauts unable to escape
Describe the Apollo 11 mission:
1969
Aldrin, Armstrong and Collins
US Flag planted
How many humans have walked on the moon?
12
Describe the Condensation/Co-Formation hypothesis for the formation of the moon:
Earth and Moon formed at the same time and place
This hypothesis is unlikely because the moon is less dense and has no iron core like Earth
Describe the Capture hypothesis for the formation of the moon:
The moon formed a great distance away from the Earth and was captured by Earth’s gravity during close encounter
Describe the Fission hypothesis for the formation of the moon:
A rapidly spinning young Earth threw off a blob which formed the moon
Describe the Giant Impact Hypothesis for the formation of the moon:
Mars sized object hit Earth causing a large blob of Earth’s outer layers melted and merged
Large amounts of Debris thrown into Earth’s orbit
Give 3 pieces of evidence to support the Giant Impact Hypothesis:
Oxygen Isotopes are the same on the moon and on the Earth
Lack of water and volatile compounds
-vaporised during the Moon’s formation
Kreep (potassium rare earth elements phosphorus) rocks found on the moon
What is the diameter of the Sun?
- 4 million km
- 100 times the diameter of the Earth (13,000km)
What is the average distance from the Earth to the Sun?
150 million km
What is the composition of the Sun?
Hydrogen 75%
Helium 25%
Traces of other elements
Describe the Sun’s surfaces:
Photosphere:
- Visible surface
- 5800k
Describe the Sun’s atmosphere:
Thin Chromosphere:
- 2000km thick
- not visible unless during an eclipse
Extensive Corona (Crown):
- Also visible during an eclipse
- Ionised gas 2 million kelvin
- Hot enough to emit X-rays
Describe two methods we can use to observe the sun:
Project an image of the sun onto paper
Use a special H-Alpha filter on a telescope
What is a sunspot?
Cooler regions on the surface (photosphere) of the Sun
-Correspond to strong local magnetic fields
Describe the structure of a sunspot:
Umbra :
- 2000K cooler than the rest of the sun (3800K)
Penumbra:
-200K cooler than the photosphere (5600K)
Describe the rotation of the Sun:
The Sun doesn’t rotate as a solid body
- the equator takes 25 days to rotate
- the poles take 36 days to rotate
What is the solar cycle?
The relative number of sunspots follows a regular 11 year pattern called the Solar Cycle
What is a butterfly diagram?
A graph of latitude of the spot on the sun’s surface
- at the beginning there are few sunspots at 35 to 40 degrees north and south
- as the solar cycle progresses, there are more spots but their positions drift towards the equator
What is the solar wind?
A steady stream of charged particles from the corona
- mostly electrons and protons
- some helium ions
Describe the two types of solar wind:
Slow (400km/s)
Fast (850km/s)
- Fast originates at the poles since the magnetic field lines are open so particles can easily escape
What is H-Alpha light?
EMR emitted by ionised Hydrogen Gas
-656nm wavelength
What features of the sun can you observe using an H-Alpha filter?
Sunspots, Solar flares, Chromosphere
Why do the Sun and Moon appear to be the same size in the sky?
Because the Sun is 400x further away but also 400x larger in diameter
Why do we not have a total solar eclipse every month?
The ecliptic and the plain of the Moon’s orbit around Earth are different
Describe a total solar eclipse:
Occurs at new moon
Moon passes directly in front of the Sun
Light from the Sun’s photosphere obscured if observer is in the umbra
Describe a partial solar eclipse:
Moon only partly obscures light from the sun
What is a lunar eclipse?
Occurs at full moon, when the Earth passes between Sun and Moon, Moon given reddish glow
What type of eclipse is most common and why?
A lunar eclipse because it is visible from most of the Earth’s night side
Why does the Moon appear red during a solar eclipse?
Because “blues bend best”
-light from the sun is refracted by the Earth’s atmosphere
In which direction does the Earth spin?
From East to west
What is a sidereal day?
The actual time it takes for Earth to spin 360 degrees on its axis
It is 23h 56min and 4.1 seconds
What is a Solar Day?
The time taken for succesive crossing of the Sun across the Observer’s Meridian
- an extra 4 minutes to allow the sun to return to the same position in the sky
exactly 24h
What is the difference between AST and MST?
AST is the measure of Solar Day
MST is the average Solar Day
Why does the Sun not move uniformly in the sky everyday?
The Earth orbits the sun in an elliptical orbit
The Earth’s polar axis is tilted to the plain of the ecliptic
- Sun higher in the sky in Summer than in Winter
Name the Aurorae?
Aurora Borealis (Northern Lights)
Aurora Australis (Southern Lights)
What casues the Aurorae?
Solar Wind
What is the speed of light in a vacuum?
3x10^8 m/s
What is one light year?
9.46x10^15 m
What is the formula for EoT?
EoT = AST - MST
What does GMT stand for?
Greenwich Mean Time
(I always thought this standed for ‘Good Morning Time’, I don’t know why, but I know always remember it through this, lol)
