Earth the basics
- Oxygen and Nitrogen make up the atmosphere
- Liquid water is found on the surface(70%)
Earth's diameter is 13,000km, its flatened by 42km making it an oblate spheroid.
Earth is round: proof...1.ship's over the horizon, 2.Satellites orbit, 3.Earth's shadow during an eclipse, 4.Aircraft fly in arcs, 5.pictures from space.
Earth rotates on the geographical poles these are found at a latitude of 90N/S, the earth is tilted 66.5 degrees.
To show where on the earth things are we use longitude(up and down-vertical) and latitude(side to side-horizontal). Latitude is measured from the equator with the tropics(cancer on top) at 23.5 degrees. Longitude is measured from the Prime meridian(Greenwhich).
The 21st of March and 22nd/23rd of September are the equinoxes-sun is directly above the equator. The 21st of June and December are the solstices-sun is directly aove the tropics.
Observations from Earth are limited by light pollution called skyglow.
Unwanted, unhelpful light is shone into the sky limited what you can see making the countryside a better suited location for taking observations.
Main sources of light pollution are:
- Sports grounds-floodlights
- Street lights
- Security lights
- Lights in car parks or shopping centers
The Brithish Astronomical Association set up the Campaign For Dark Skies in 1989 it aims to represent the intrests of people to 'protect' the night sky. The main problem is that lights are inaffective and there is lots of light wasted as its directed upwards blocking out the view of the sky.
The first accurate measure was done by Eratosthenes in the 3rd century BC.
He used a shadow stick at two seperate locations.
He compared the length of the shadow cast from a stick in Alexandria and Syene on the summer solstice. Syene is on the Tropic of Cancer so there was no shadow. Alexandria is 790km away from there the sun was 7degrees away from being directly overhead.
Because he knew there was 360 degrees in a circle meaning when its timesed upto make the whole circle the Earth's circumference was worked out to be 39 500km.
Eratosthene worked out the circumference to within an accuracy of 5%.
- Earth's atmosphere is made up of: 78% nitrogen, 21% oxygen, 1% argon, 0.04% carbon dioxide, an average of 1% water vapour and a little bit of neon, helium and methane.
- As you get higher up the atmophere gets thinner at 10 000km the atmosphere merges with outer space.
- Positives: 1.Absorbs lots of harmful radiation, 2.Helps to prevent skin cancer, 3.Regulates the temperature, 4.Gives us oxygen, 5.Meteor protection
- Negatives:1.Light is refracted-stars twinkle, 2.Selective scattering of shorter wavelengths-makes the sky appear blue, 3.Absorbs and reflects most wavelegths meaning no observations can be taken.
Specific effect on wavelegths
Radio-reflected by electrons in ionosphere
Microwaves-absorbed by water vapour and oxygen
IR-absorbed by water vapour, carbon dioxide, and methane
UV-absorbed by ozone and the shorter wavelegths are absorbed by oxygen
X-ray and Gamma-absorbed by oxygen and nitrogen, X-rays ionise and Gamma excite the nuclei so both lose their energy so can't break through the atmosphere.
Telescopes and observatories
2 types of telescope
- Reflector-uses mirrors to create an image in the eye piece.
- Refractor-uses two lenses, an objective lens and an eye piece
Relectors are more commonly used becasue its easier to manufacture as they are lighter, have less imperfections and they are cheaper.
Telescopes with larger appatures collect more light giving better quality images.
Atmospheric properties because of this many telescopes are found at high altitde
Geographical location mainly for the first consideration.
However orbital telescopes are preferable
No atmosphere, No light pollution(minus natural), No eather(minus solar wind), longer observation periods, and you can detect all wavelengths
Problems: Cost, lifetime and hard to fix/ maintain
They must be kept cool so as not to influnece recordings so they use coolents and open design.
Van Allen Belts
They are two doughnut shaped rings which surround earth starting/ending at the Earths pole's. They are made of spiralling high-energy particles which are kept in place by the Earth's magnetic field.
- More compact belt
- 600km-10 000km above Earth
- Made of high energy protons from cosmic rays and atmospheric atoms colliding
- It gives of radiation can be harmful in large doses to astronauts and equipment
- Discovered 1958, by Explorer 1, confirmed by Explorer 3 and Sputnik 3 in the same year
- More difuse belt, more dynamic(moves more), wider
- 15 000km- 65 000km above Earth
- Made of electrons and other charged particles from the sun, made from solar activity
- Discovered 1958, by Pioneer 3, confirmed by Sputnik 2 and 3
Moon the basics
Moon the basics
- Earth's only natural satellite
- Diameter of 3500kmMean orbiting dstance(around Earth) of 380 000km
- Gravity is 1/6 of Earth's = no real atmosphere but does control the tides on Earth
- We only ever see one side of the Moon because the orbital and rotational periods are almost identical.
- Dark grey areas-Umbra, Seas, Maria,iron rich basaltic rock
- Light grey areas-Penumbra, Highlands, Terrae, grained igneous rock
- Rilles-thin channel indentations can go in any direction caused by lava flow cutting paths
- Wrinkle ridges-ridges from surface bukling under pressure when lava was cooling
- Dark side of the moon has nearly no seas and has many more mountains as well as craters showing the rock is older.
NASA's Apollo project began in 1960
Aims: 1. Send a man to the moon and return them safley, 2.Collect lunar samples, 3.Start ongoing experiments up on the surface and 4.Win the space race.
Goals achieved 20.7.1969, 2.5 hours spent on the surface.
12 astronauts have been on the moon, each set deploys an Apollo Lunar Surface Experiment Package where they land, these send back data even after the astronauts return.
Included in the ALSEP packs are instruments to:
- Analyse the Moons interior structure
- Moniter pressure and composition of the Moon's atmosphere
- Moniter gravity
- Moniter meteor debry
- Moniter lunar dust
- Analyse the lunar surfaces thermal and elecrtical properties
Some contain LRRR(Laser Ranging RetroReflectors) (reflect lasers to Earth to measure the distance between the two accuratly)
Formation of the Moon
4.5 billion years ago
Many theories: co-formation, capture and fission for example.
Generally accepted theory is the Giant Impact Hypothesis.
1.Earth is hit by a mars sized object named Theia
2.Earth loses a bit
3.Earth's lost bit and Theia merge making the Moon
1.The Moon and the Earth have almost identical isotopes of oxygen in their rocks.
2.There is no water or volitile compound present on the Moon-lots of heat and pressure needed for this to evaporate.
3.K.R.E.E.P levels-K potassium, Rare Earth Elements (and) Phosporus
This was agreed in 1984 since then compter simulations have also been run and support the hypothesis.
Sun the basics
Sun=Star in the center of our solar system, main sequence(Hertzprung Russle diagram)
Diameter=1.4 million km
150 million km/ 1AU from Earth
75% Hydrogen and 25% Helium
The sun has three visible layers
1. Photosphere-visible'surface', 5800K(Kelvin)
2. Chromosphere-thin 'sphere of colour' like an outline of the sun only really visible during totallity in a solar eclipse, 2000km thick
3.Corona-'crown', made of ionised gas which is hot enough to emit X-rays, 2million K, combined with chromosphere it makes the sun's atmosphere
1.Nuclear fussion in the core
3.convected to photosphere
4.Radiated into space
Nuclear fussion is a proton-proton chain
Hydrogen(2 nucleus)+Proton=Helium(3 nucleus)
Helium(3 nucleus)+Helium(3 nucleus)=Helium(4 nucleus)+Proton+Proton
*the = sign actually represents an arrow NOT an equals
Observing and Sunspots
Two safe ways of observing the sun:
1.H-alpha or Mylar filter-absorbs all wavelegths other than 656 nm
2.Indirect projection-image projected then view projection
Cooler parts of the sun's photosphere look like small dark patches on the surface
Sunspots never reach the tp of the sun as strong localised magnetic fields stop solar material being moved by the convection currents, because they don't reach the top they become cooler.
They usually form in pairs (reflection) due to opposite polarity at each pole.
Two parts of a sunspot:
1.Umbra-darker, 2000K cooler
2.Penumbra-lighter, 200K cooler
Traking sunspots(butterfly diagram) shows the sun doesn't rotate as a whole...
36 day rotational period at the poles
25 day rotational period at equator
Sunspots last a few days up to a few weeks
There is an 11 year patern in sunspot activity
Sunspots start at between 35-40 degrees N/S and finish at between 5-10 degrees N/S
Two types of solar wind:
Made of charged particles-mainly protons and electrons
Flows from the sun's corona in all directions
Travels at 400km/s generally
Thought that corona's high temp allows the particles to escape the sun's gravity
From coronal holes-cool regions in the corona near the sun's poles
Because thereare open magnetic field lines leting particles escape more easily
Speeds of up to 850km/s
Many probes sent just to view sun on different wavelegths:
X-ray apperance, can show the heat of the photosphere
H-alpha apperance, allows features to be seen more easily
Sunspots-cooler regions on the surface of the sun
Active region-part of the sun where lots of energy is being given off
Filament-clouds of gas which are cooler than the sun's atmosphere, they look like shadows against the brighter photosphere
Prominence-clouds of cooler gas in the sun's atmosphere
Solar flare-sudden release of energy, a burst
*Photosphere acts as the base
Other stuff- Lunar phases
The lunar cycle take 29.5 days(1 lunar month), the cycle goes
9. Back to new Moon
Awhole orbit of the Earth takes an extra 2.2 days because the Earth has moved significantly in its orbit around the sun.
This is when the sun is totally blocked by the moon.
A total eclipse is visible from only a small area with a larger area experiencing a partial solar eclipse(partial blockage of the Sun by the Moon).
Totallity is when the sun is totally covered, at this point you can view some stars, the temperature drops, you can see the Sun's corona and Baily's Beads(bright spots of sunlight where the Sun's rays shine through the Moon's valleys)
Solar eclipses occur at a new Moon. But only when the Moon is in alignment as it orbits at a tilt of roughly 5 degrees compared to the Earth's orbit around the Sun.
This is when the Earth gets between the Sun and the Moon, the Earth's atmosphere refracts the Sun's light so the moon appears an orange/red colour.
This ocurs at a full Moon.
If parts of the Moon are not in'shadow' then it is only a partial lunar eclipse
Sidereal day=23h 56mins, the time it takes the Earth to complete a full rotation.
Solar day=24h, the time it takes for the sun to appear at the same position in the sky.
Apparent solar time=time based on the position of the Sun which we actually see.
Mean solar time=time based on the average position of the Sun for that location.
They are slightly different because the Earth orbit is ecliptical not circular, and the Earth is tilted so the sun is higher in the summer and lower in the winter.
The difference between the two is called the Equation Of Time(EOT). EOT=apparent solar time-mean solar time(GMT)
Working out mean solar time
Using a sundial-always take into account the EOT and minus/add it to the apparent solar time.
Using a Shadow stick-look at when the shadow is smallest, compare this to the mean solar time and you can work out what the EOT is. You can also work out your longitude as every 4mins past 12(GMT) is 1 degree west of Greenwhich ad vice versa.
Popularly known as the Northern/Southern lights.
Normally only visible at high latitude, but can be visibel at lower latitude if solar activity is very high.
1.Electrons from solar wind are accelerated to high speeds in the Earth's magnetic field.
2.The electrons excite atoms/molecules of oxygen and nitrogen in the top of Earth's atmosphere.
3.When the atoms/molecules de-excite they emit light at wavelegths characteristic to the element.
*Greena nd red are from oxygen, purple and red are from nitrogen