Unit 1 Flashcards
State 3 ways in which the earth is different to all of the other planets in our solar system
- It has an atmosphere of mainly oxygen and nitrogen
- It has liquid water
- It supports life
What is the shape of the Earth?
What is the average diameter of the Earth?
The Earth is an Oblate sphereoid - this menas that it is egg shaped. It is wider at the equator than it is at the poles
The average diameter of the Earth is 13000km
Give 5 pieces of evidence that the Earth is spherical
- Satellites orbit the Earth
- Ships disappear over the horizon
- The Earth casts a curved shadow during an eclipse
- Aircraft fly in arcs (not straight lines)
- Images of the Earth from space
What is the zodiac?
How do we know that the zodiac exists?
The zodiac is the place on which all of the planets orbit around the sun
We know that it exists becuase all of the planets and the sun orbit in the zodiacal band (we see them travelling through the same area of the sky)
What is the polar axis of the earth?
What is the angle that the axis makes to the ecliptic?
The line around which the earthrotates
66.5 degrees
Label each part of this diagram
What are the tropics of Cancer and Capricorn
these are the higest and lowest lattitudes where the sun appears at the zenith.
the sun is at the Zenith of th etropic of cancer on June 21st (summer solstice) and at the Zenith of the tropic of capricorn on December 21st (Winter solstice)
What is lattitude and what it it measured in
Lattitude tells you how far north or south you are.
It is measured in Degrees where 0o is at the equator. 90o is at the north pole and -90o is at the south pole
What is Longitude and what is it measured in?
Longitude tells you how far round the earth in the East - West plane you are.
It is measured in degrees from the Grenwich meridian. The Scale runs from 0 to 24 hours
What is light pollution?
What are the causes?
Light pollution is also known as skyglow. it is when man made light creates a background haze which blocks out the light from the stars.
It is caused by:
- sports floodlights
- streetlights
- Lights from car parks and shoping centers
- domestic security lights
How did Eratosthenes measure the circumference of the Earth?
- He used a shadow stick to prove that at Syene the sun was at the zenith. This is seen becuase the stick causes no shadow
- On the same day at Alexandria a shadow is cast, this is used to find the angle that the sun makes to the zenith
- The distance between Alexandria and Syene is measured. Then the proportion of the angle between the two cities of 360o is the same as the proportion that the distance between the cities is of the circumference of the Earth.
What are the approximate proportions of the gasses in the atmosphere of the earth?
Nitrogen - 78%
Oxygen - 21%
Argon - 1%
Water vapour - Variable (average 1%)
Carbon dioxide - 0.04%
(Yes - I know this all adds up to 101.04% but thats just the way it is)
What are the benefits of our atmosphere to people?
- Absorbs solar ultraviolet radiaiton - protects us from skin cancer and sunburn
- Absorbs other harmful radiation from space - gamma rays and x-rays
- Regulates the temperature of the earth - without it the earth would be too cold for life to exist
- Provides oxygen to breathe - we rely on respiration to transfer energy
- Partial protection from meteoriods - air resistance (friction) means most of them will burn up as the enter the atmosphere and not hit the surface of the earth
What are the problems for astronomers of our atmosphere?
- Refraction - The atmosphere causes light to bend, resulting in stars that twinkle and limits to the resolution of telescopes
- Scattering of blue light - this makes the sky appear blue and stops us from viewing the stars during the day
- Absorbtion and reflection of electromagnetic waves - only visible light and radio waves reach the surface of the earth
Explain why we cannot build an x-ray telescope on earth
How do we get round this problem
X-rays are absorbed by the atmosphere so they do not reach the surface of the Earth
We can aviod this problem by building a telescope in space, above the atmosphere of the Earth
Explain how the two types of telescopes work
Why are larger telescopes always reflecting telescopes
Refracting telescope - this uses a convex lens to collect and focus the light
Reflecting telescope - this uses a curved mirror to collect and focus the light
Larger telescopes are always reflecting telescopes becuase very large lenses will sag and deform under their own weight
What does the word resolution mean?
This means the ability of a telescope to tell the difference between two objects that are very close together. The greater the resolution of a telescope, the more detail it can pick out.
What are ideal observing sites for building a telescope on the earth?
Good atmospheric conditions - A place where it rarely has cloud cover, has low humidiy (water vaopur) and low air turbulance (not very windy)
High up - reduces the thickness of the atmosphere that it needs to look through
Away from major towns and cities - this reduces the effect of light pollution
Geographic factors - good road acces, low likelyhood of adverse events such as earthquakes
What are the advantages and disadvantages of building telescopes in space?
Advantages
- No atmosphere to blur the image
- No light pollution
- No problems with weather
- No daytime - can observe 24h a day
- Can detect wavelengths that cannot penetrate the atmosphere - such as infrared, x-ray and gamma ray
Disadvantages
- Short lifetime
- Very hard to maintain - you have to send an engineer into space
- Very expensive to build and launch
State two current space telescopes
What is the space telescope currently under construction
Current - Hubble and Spitzer
Under construction - James Webb
What is the Van Allen belt?
How does it protect us from solar radiaiton?
The Van Allen belts are two rings of particles that are held in place by the magnetic field of the Earth. There is and inner belt containing protons formd by collisions between cosmic rays and atoms in the atmosphere and an outer belt consisting of charged particles emitted by the sun.
It protects us from solar radiation because it traps harmful charged particles from the solar wind, stopping them from entering the atmospere of the Earth
What are the problems to astronauts caused by the lower inner Van Allen radiaiton belt?
The charged particles can damage the cells of astronauts (leading to cancer as they ionise DNA) and can damage sensitive scientific equipment.
What is the solar wind?
How fast does it travel?
The solar wind is a stream of charged particles emitted from the sun, it is mostly protons and electrons
The slow solar wind travels at 400km/s and the fast solar wind travels at 850 km/s
How does the solar wind change the size of the Van Allan belts?
When there is a period of high solar wind activity the Van Allen belts swell and become larger, as they are holding more charged particles
They become smaller during periods where there is a low solar wind
What is the diameter of the moon?
What is the average distance that the moon orbits the earth at?
The diameter of the moon is 3500km
the average distance that the moon orbits the earth is 380 000km
What is the period of orbit of the moon?
The moon orbits the Earth once every 27.3 days
Explain why we only see one side of the moon from the Earth
The rotational period of the moon is 27.3 days, this is exactly the same as its orbital period. The means that it rotates as it orbits at exactely the right rate to keep one side of the moon facing the Earth.
This is a phenomenon called tidal locking
State the name and temperature of each of these layers of the sun
- Corona - 2 million Kelvin
- Chromosphere - 800,000 Kelvin
- Photosphere - 580 Kelvin
- Convection zone - 2 million Kelvin
- Radiationzone - 8 million Kelvin
- Core - 15 million Kelvin
Describe how the sun transfers energy as light and heat
Explain why this process only occurs in the core
The sun transfers energy by nuclear fusion. This is when hydrogen nuclei (protons) are fused together to form a helium nucleus, releasing energy in the process.
This only occurs in the core because this is the only area that is hot enough for the protons in the sun to overcome the repulsive force between them and get hot enough to fuse together.
Describe how the numbers of sunspots changes over time
Describe how we can represent this
The number of sunspots changes in and 11 year cycle, the greatest numbers of sunspots occur in the middle of the cycle. The cycle starts with a few sunspots at 30o-40o lattitude.
They then gradually move towards the centre until the cycle ends with them at about 5o to 10o lattitude. The number of sunspots gradually increases until the middle of the cycle, then gradually decreases again.
The cycle of sunspots can be represented on a butterfly diagram.
Explain why the phases of the moon occcurs
The phases of the moon occurs becuase as the moon orbits the earth the side facing the sun is light and the side facing away from the sun is in shadow. As we are always viewing the moon from the centre, this means we see different amounts of the shadow and light side depending on the positions of the earth, moon and sun.
When the earth is between the moon and the sun we see all of the light side, this is a full moon. When the moon is between the Earth and the Sun we see all of the shadow side, this is a new moon.
How much longer is the lunar month (a cycle of the phases of the moon) when compared to the obital period of the moon.
Explain why this is
The full lunar cycle is 2.2 days longer (29.5 days) than the orbital period of the moon (27.3 days)
This is becuase it takes it takes 27.3 days for the moon to move from being between the Earth and the Sun back to being in the same position relative to the earth, but as the Earth has orbited round the sun, it needs to travel slightly further back round the Earth to be between the Sun and the Earth again.
Describe the difference between a solar and a sidereal day.
Explain why this difference occurs
A solar day is the time taken for the sun to move from the meridian back to the meridian. This takes exactly 24 hours.
A sidereal day is the time taken for a star to move from the meridian back to the meridian. this takes 23h and 56 minutes and is the time it takes for one complete rotation of the earth.
This difference is caused because in the time it takes for the earth to rotate once it has moved a total of 4 arc minutes (1 degree) in its own orbit around the sun. This means that the earth has to do this extra rotation to get the sun back into the same place, which takes an extra 4 minutes.
