# OCR 21st Century Science P7

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• Created by: Caroline
• Created on: 21-06-13 12:10
How long does it take the Earth to orbit the Sun?
365.25 days.
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How long does it take the Moon to orbit the Earth?
28 days.
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How long does it take the Earth to rotate once on its axis?
24 hours.
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What is a sidereal day?
The time taken for a star to return to the same position in the sky.
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How long is a sidereal day?
23 hours and 56 minutes.
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Which way do stars travel across the night sky?
East to West.
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How many degrees does the Earth have to spin in order for a star to get to the same position in the night sky?
360degrees.
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In which direction do the sun and moon travel across the night sky?
East to West.
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What is a solar day?
The time taken for the sun to appear in the same position in the sky.
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How long is a solar day?
24 hours.
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How long does it take the Earth to complete one rotation?
24 hours.
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Why are sidereal and solar days different lengths? (Part 1)
The Earth is orbiting the sun as well as rotating on it's axis. This means that when the sun has rotated 360 degrees, the sun will not be directly above the Earth anymore, as the Earth has moved slightly round it's orbit.
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Why are sidereal and solar days different lengths? (Part 2)
This means that the Earth has to rotate slightly more than 360 degrees in order for the sun to return to the same place in the sky.
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Why do stars appear to be directly above the Earth again after a 360 degree rotation of the Earth?
They are very distant.
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Which seems to travel fastest, the sun or the moon?
The sun seems to travel faster than the moon, the moon taking 25 hours to appear in the same position in the sky. This is because the moon orbits the Earth in the same direction as the Earth is rotating.
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Why can we see different stars throughout the year?
As the Earth moves around the Sun, the direction we face changes slightly each day. This means we see a slightly different patch of sky each night - hence the stars are different.
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What is an Earth year?
The time it takes the Earth to orbit the Sun once.
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What does this mean regarding the stars we see?
On the same day each year we should be able to see the same stars in the night sky.
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How many phases of the moon are there?
8.
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What are the phases of the moon?
Full Moon, Waxing Gibbous, 1st Quarter, Waxing Crescent, New Moon, Waning Crescent, Third Quarter and Waning Gibbous.
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Does the Moon produce light?
No, it reflects the sun light.
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Which part of the moon is lit up?
The bit that is facing the sun.
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What are the two types of eclipses?
Lunar eclipse and Solar eclipse.
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Explain how a lunar eclipse occurs.
When the Earth is in between the Sun and the Moon, it blocks the sunlight from getting to the Moon, so almost no light is reflected from the Moon. This means we cannot see it.
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What is the difference between a partial lunar eclipse and a full lunar eclipse?
A partial lunar eclipse is where only part of the Moon is in the Earth's shadow, meaning some light is reflected by the moon. A full lunar eclipse is when the whole of the moon is in the Earth's shadow, so absolutely no light is reflected.
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Which type of lunar eclipse is more common?
Partial.
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Explain how a solar eclipse occurs.
When the moon is in between the Sun and Earth, it blocks the sunlight and stops it from reaching the Earth.
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How do the different places of Earth see a lunar eclipse?
From some places on Earth, the sunlight will be completely blocked out, making a total solar eclipse. On many places on Earth only part of the sunlight is blocked out, and in most places no sunlight it blocked out.
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Why are eclipses not very frequent?
The Moon orbits the Earth at an angle to the Earth's orbit to the Sun, so the Sun, Moon and Earth do not line up very often.
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Why are partial eclipses more frequent?
The Sun, Moon and Earth don't have to line up perfectly for this to happen, only a small section of each has to be in line.
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How are the positions of stars measured?
By angles seen from Earth.
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Which two points were picked to measure from?
1.The Pole Star and 2.The Celestial Equator.
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What are these and why were they chosen?
The Pole Star is a star that doesn't seem to move as it is almost directly above the North Pole of the Earth. The Celestial Equator is an imaginary plane running across the night sky that extends from the Earth's equator.
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What are the two angles that are used to measure positions in the sky?
1.Declination. 2/.Right Ascension.
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What does Declination measure?
Declination measures the celestial latitude, measured in degrees. (How high up the star is in relation to the celestial equator.)
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What does Right Ascension measure?
Celestial longitude, measured in degrees or time. (How far across the star is.)
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Why is it possible to have an angle measure in time?
Because the Earth turns 360 degrees every 24 hours.
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How does Right Ascension increase?
The further East you go, the bigger the Right Ascension.
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What are the 'Naked Eye' Planets?
Planets that you can see without using a telescope. These are Mercury, Venus, Mars, Jupiter and Saturn.
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In which direction do planets seem to moving in the night sky?
West to East.
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What are fixed stars?
Distant background stars that stay in the same position in the sky year after year.
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The process in which a planet seems to change direction and create a loop in its path.
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To which planets can this happen to?
The outer planets - Mars, Jupiter, Saturn, Uranus and Neptune.
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How does it happen? (Part 1)
1.From Earth, Mars seems to be moving to the left, against the fixed stars. 2.As the Earth's orbit is small than the orbit of Mars, after a few months, the Earth over takes Mars, which makes Mars look like it is travelling to the right.
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How does it happen? (Part 2)
3.After a few more months, Earth is moving horizontally downwards in it's orbit, but Mars is still moving horizontally, making it seem like it is travelling to the left again against the fixed stars.
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Which planet moves with Retrograde motion the most frequently?
Mars, it appears to move with retrograde motion once every two years or so.
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Why do planets that are further out move with retrograde motion less frequently?
They are slower moving.
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What factor affects the speed of a wave?
The density of the substance or medium it is travelling in.
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What happens when a wave crosses a boundary between two substances?
It changes speed.
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Give an example of these two substances.
Glass and Air.
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What is the equation for wave speed?
Wave speed = frequency x wavelength.
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Which part of this equation is fixed for each type of wave?
Frequency.
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What does this mean regarding the wavelength?
It must also change. Eg. if speed decreases, wavelength must decrease.
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What is refraction?
The change in speed and wavelength can cause a wave to change direction too.
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How does refraction work?
If a wave hits a different medium at angle, part of the wave hits the boundary first and slows down. The other part of the wave carries on at the same speed as it has not yet hit the boundary. This causes the wave to change direction.
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What happens to a wave if it hits a different medium straight on?
It continues travelling in the same direction. The wavelength has become shorter but the frequency remains the same.
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What does a convex lens do to waves?
Focuses them to a focal point to form an image of a object.
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What is another name for a convex lens?
A converging lens.
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What is the normal?
The line at right angles to the boundary at the point where the ray enters or leaves.
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What happens when a wave hits a lens?
As it travels from air to glass, the wave slows down, causing it to bend towards the 'normal'.
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What happens when it comes out of the other side?
As the wave travels from glass to air, it speeds up, bends away from the normal.
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What does the curvature of the lens do?
It makes all of the waves hitting the lens converge to the same focal point, where an image is formed of whatever the light is coming from.
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Complete the sentence. Different wavelengths of light refract by...
Different amounts.
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What is white light made up of?
A mixture of lots of wavelengths of coloured light.
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What happens to rays of light as they pass through a rectangular prism?
A rectangular prism has parallel boundaries, so the rays bend one way when they enter, and then back again by the same amount as they leave. The light entering the prism is parallel to the light leaving the prism so white light is produced.
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What happens to rays of light when they pass through a triangular prism?
The boundaries are not parallel, which means the different wavelengths are refracted different amounts. When they leave the prism, a spectrum of light is formed.
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Which colours are the spectrum made up off?
Red, Orange, Yellow, Green, Blue, Indigo and Violet.
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Which colour is refracted the most?
Violet.
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How can you remember this?
Red is Refracted, Violet is Very refracted.
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What is the principle axis?
The line that runs straight through the middle of the lens.
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What is a focal point?
The focal point is where rays initially parallel to the principal axis meet.
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How many focal points do all lenses have? Where are they?
2 - One in front of the lens and one behind it.
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What is the focal length?
The distance between the middle of the lens and the focal point.
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Complete the sentence. The more powerful a lens..
The more strongly it converges the rays.
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What does this mean regarding the focal length?
As the rays are getting converged more strongly, the focal length is shorter.
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What is the equation for working out Power?
1/Focal Length.
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What is Power measured in?
Dioptres.
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Work out the power of a lens with a focal length of 0.2m.
Power = 1/0.2 = 5D.
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How do you make a more powerful lens out of the same material?
Make it with a more strongly curved surface.
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How does light reach a lens from an object in space?
The rays are parallel to each other.
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Give the stages on how to draw a ray diagram for a point object. (Eg. a star.) (Part 1)
Draw 3 parallel rays, one to the centre of the lens, one towards the top and one towards the bottom. Make sure you only draw the lines to the centre line of the lens. 2.Draw on the focal point.
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Give the stages of how to draw a ray diagram for a point object. (Eg. a star.)(Part 2)
3. Extend the middle line past the focal point as this does not get refracted. 4.Extend the other two lines to meet at the focal point. 5.This is where the image will be.
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Give the stages of how to draw a ray diagram for an extended source. (Eg. a galaxy.) (Part 1)
1.Treat two opposite edges of the extended source as point sources. 2.Carry out the same steps for both point sources. 3.The image will form in between the two focal points.
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How many lenses are in a simple refracting telescope?
2.
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What type of lenses are they?
Converging lenses with different powers.
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What are these two lenses called?
Objective lens and eye piece lens.
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Which lens is the most powerful?
Eye piece.
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Why?
It magnifies the image so we can view it.
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What does the objective lens do?
It collects the light from the object being observed and forms an image of it.
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How are the two lenses aligned?
They have the same principal axis and their focal points are in the same place.
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What does the objective lens do to the rays?
Converges the parallel rays to form a real image between the two lenses.
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What does the eye piece lens do?
The eye piece lens is much more powerful than the objective lens (it is much more curved). It acts as a magnifying glass on the real image and makes a virtual image - where the light entering the eye lens appears to have come from.
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What is the equation for working out Magnification of a telescope?
Magnification = Focal length of objective lens/Focal length of eye lens.
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Work out the Magnification of a telescope when Fo=4.5m and Fe=0.1m.
Magnification = 4,5/0.1 = 45.
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What do most astronomical telescopes use?
A concave mirror.
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What is this used instead of?
The convex objective lens.
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What is a concave mirror?
A mirror that is like a portion of a sphere. The shiny bit is on the inside edge of the curve.
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Where is the centre of curvature?
The centre of the sphere.
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Where is the vertex?
The centre of the mirror's surface.
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What is the axis?
The line running from through the centre of curvature and the vertex.
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Where is the focal point found?
Half way between the centre of curvature and the vertex.
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What happens to the rays as they hit the mirror?
Rays that are parallel to the axis (those from a distant star), reflect and meet at the focal point.
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How can this be used in a telescope?
By putting a lens by the concave mirror to act as an eye piece, you can form a magnified image.
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Why are mirrors used instead of lenses?
To collect the light from distant objects you would need an incredibly large objective lens, which would not be supported when the telescope is moved around in space. Mirrors also stop any light loss from passing straight through the glass lens.
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What is diffraction?
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What happens to waves when they pass through a gap or past an object?
They diffract at the edges.
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What does the amount of diffraction depend on?
The size of the gap relative to the wavelength of the wave.
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Complete the sentence. The narrower the gap or the longer the wavelength...
The more the wave diffracts.
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What is classed as a narrow gap?
A gap about the same size as the wavelength of the wave.
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Does light have a small or large wavelength?
Very small.
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When can you notice that light has been diffracted?
When the gap is extremely small.
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How much radiation reaches us on Earth from objects that are extremely distant?
Very little.
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What needs to be used to see distant objects and why?
You need to use a telescope with a huge object lens (or mirror) so that enough radiation can be collected to see the object.
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What is the aperture?
The diameter or the lens.
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Why are lens with bigger apertures better to use for studying distant objects?
The bigger the aperture, the more radiation can get into the telescope and the better the image formed.
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Because all waves diffract when they pass through a gap.
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What does this cause the image to do?
Blur.
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What would happen if you looked at a point source like a star with an aperture that is too small?
The dot would be dimmer and would be surrounded by diffraction rings which would get dimmer the further away from the image they are.
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How can you get round the problem?
Have an aperture that is much wider than the wavelength of radiation you want to look at. This way the radiation will pass through the aperture and into your telescope with very little diffraction, meaning you get a sharp image.
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Other than the triangular prism, what is another way to make a spectrum of visible light?
By using a diffraction grating.
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How does this work?
It has very narrow slits which are small enough to diffract light. When white light passes through the gaps, the different wavelengths of coloured light are all diffracted by different amounts.
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What does this create?
A spectrum of coloured light.
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What can astronomers use these spectra for?
Analysing the light coming from stars.
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What is Parallax?
An apparent change in the position of an object in the night sky against a distant background. It makes closer stars move relative to distant ones over the course of a year.
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How long does it take the Earth to get to the other side of its orbit?
6 months.
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What is the definition for the parallax angle?
Half the angle moved against distant background stars over 6 months.
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Complete the sentence. The closer the star...
The bigger the parallax angle.
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What is the parallax angle often measured in?
Arcseconds/seconds of arc.
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How any arc seconds are there in a degree?
3600.
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Why is parallax useful?
It is useful for calculating the distance to nearby stars.
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What happens to the parallax angle as the star gets further away?
It gets smaller.
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What is the distance to the star usually measured in?
Parsecs.
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How many light years is roughly equal to a parsec?
3 light years is roughly equal to a parsec.
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How big are interstellar distances?
Usually a couple of parsecs.
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What is the definition of a parsec?
The distance to a star with a parallax angle of 1 arcsecond.
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What are interstellar distances?
Distances between stars.
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What is the equation for working out the distance to a star in parsecs?
Distance = 1/angle
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What is the abbreviation for parsecs?
pc.
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What is the abbreviation for arcseconds?
arcsecs.
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Work out the distance to a star that has a parallax angle of 0.4 arcseconds.
Distance = 1/0.4 = 2.5pc.
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What does the absolute brightness of a star depend on?
Its size and temperature.
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Complete the sentence. The bigger and hotter a star is..
The more energy it gives out, so the brighter it is.
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What does the apparent brightness of a star depend on?
Its luminosity and its distance from Earth.
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Why do stars look dimmer the further away you are from them?
As you move away from a star, the energy that reaches you gets less and less.
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What are Cepheid Variables?
Stars that pulse in brightness.
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What determines how quickly a Cepheid Variable pulsates?
Its luminosity.
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Complete the sentence. The greater the luminosity...
The longer the time between pulses.
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What is a period?
The amount of time between pulses.
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Complete the sentence. The longer the period...
The further away the star is.
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How can astronomers work out the luminosity of a Cepheid Variable?
It is worked out from its period.
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How can astronomers work out the distance to a Cepheid Variable?
By comparing the luminosity and the apparent brightness of the star.
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If you look up at the night sky, how are the stars arranged?
Most of the stars are appear to be concentrated in a bright ***** across the sky.
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What is this *****?
The Milky Way.
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What are the stars like that are away from this *****?
There are much less of them.
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Our Sun is one of approximately how many stars in the galaxy?
10^11.
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What type of galaxy is the Milky Way?
A spiral galaxy.
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Why do we see it as a *****?
We are part of its disc so we see it side on.
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Who was the debate about the structure and size of the universe between?
Shapley and Curtis.
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What are nebulae?
Faint, fuzzy objects.
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How did these nebulae seem different?
Some seemed spiral shaped, but others just looked like blobs.
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What were Shapley and Curtis arguing about?
What these nebulae were and where they were.
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What was Shapley's argument?
The Universe was just one gigantic galaxy about 100 000 parsecs across. Our Sun and Solar System were far from the centre of the galaxy. The nebulae were huge clouds of gas and dust and relatively nearby and they were part of the Milky Way.
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What was Curtis' argument?
The Universe was made up of lots of galaxies. Our galaxy was smaller that Shapley suggested - about 10 000 pc across, with the Sun at or very near the centre, The spiral nebulae were other very distant galaxies separate from the Milky Way.
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What was the outcome of the debate?
1.Shapley was right in saying that the Solar System is far from the centre of our galaxy, but Curtis was right that there are many galaxies in our Universe. (At least 100 000 000 000 of them.) 2.Curtis was also right about the spiral nebulae.
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Who helped solve the Curtis-Shapley debate? How?
Hubble - with his observations of the Andromeda nebula.
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How did he do this? (Part 1)
He used images taken by the largest telescope at the time, and found that this fuzzy blob contained many stars, some of which were Cepheid Variables.
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How did he do this? (Part 2)
He calculated the distance to the Andromeda nebula by working out the distance to the Cepheid variables within in, using their period and luminosity.
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How did he do this? (Part 3)
He found it was about 2.5 million light years away which is much further than any other stars in our galaxy. He studied other spiral nebulae and found a similar result.
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What did he conclude?
All of the spiral nebula were too far away to be in our galaxy so they must all be seperate spiral nebulae themselves.
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What units are usually used to measure intergalactic distances?
Megaparsecs.
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Why?
The distances are too huge to be measured by parsecs.
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How many kilometres is roughly equal to a mega parsec?
3 x 10^11.
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What is the distance to the nearest galaxy?
Just under 0.8Mpc.
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What is red shift?
As a galaxy is moving away from us, the wavelength of the light from it changes. It shifts from blue to red.
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How can you use red shift to work out how fast a galaxy is moving away from us?
By seeing how much the light has been red-shifted, you can work out the speed at which it is moving away from us.
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What pattern did Hubble find?
The more distant the galaxy, the faster it moves away from us.
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What does this suggest?
The whole universe is expanding from a single point.
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How could this be explained?
By the initial explosion millions of years ago that started off the expansion.
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What is this?
The Big Bang theory. It is thought that all matter and energy in the universe was compressed into a very small space, and then it exploded 14 million years ago and has been spreading out ever since.
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Is red shift easy or hard to measure?
Easy.
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What is Hubble's law?
Speed of recession = Hubble constant x distance.
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What are each measured in?
Either: km/s, s-1 and km. Or: km/s, km/s per Mpc and Mpc.
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What is the value of the Hubble constant?
Roughly 2 x 10^18 or 70/km/s per Mpc.
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Find the distance to a galaxy that has a recession of 475km/s.
Distance = speed of recession/hubble constant. 475/(2x10^18) = 2.375 x 10^20 km.
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How can we get a better value of Hubble's constant?
By using data on Cepheid Variables from distant galaxies.
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What is the kinetic theory?
Gases consist of very small particles which are constantly moving in completely random directions. They constantly collide with each other and with the walls of their container. The particles hardly take up any space. Most of the gas is empty space.
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What happens if you increase the temperature of something?
You give it's particles more kinetic energy. This means they move about more quickly and they vibrate more.
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What happens if you cool something down?
You reduce the kinetic energy of the particles.
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What is the coldest that anything can ever get?
-273degrees celcius.
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What is this temperature known as?
Absolute zero.
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What is the kinetic energy of the particles like at absolute zero?
The particles have as little kinetic energy as it's possible to get.
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What is another scale used for temperature?
Kelvin.
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If you had a temperature change of 1degree celcius, what is the temperature change in Kelvin?
1K.
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How many kelvin is -273degrees celcius?
0K.
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How do you convert from kelvins to degrees celcius?
Subtract 273.
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How do you convert from degrees celcius to kelvins?
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How many kelvins are there in 34 degrees celcius?
307.
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How any degrees celcius are there in -67 kelvins?
-340.
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How are kinetic energy and temperature related?
Kinetic energy is proportional to temperature.
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Give the statement for this.
The temperature of a gas (in kelvins) is proportional to the average kinetic energy of it's particles.
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How are pressure and volume related?
They are inversely proportional at a constant temperature.
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What happens when gas particles collide with each other?
They exert a force on each other as they have some mass.
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What happens to gas particles in a container?
They collide with the container walls, exerting a force, causing an outwards pressure.
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What would happen if you put the same amount of gas in a bigger container?
The pressure would decrease as there would be fewer collisions between the gas particles and the container walls.
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What happens if the volume is reduced?
The pressure increases and the particles collide with the walls more often.
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What is the equation relating pressure and volume?
Pressure x volume = constant.
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A gas at a constant temperature in a 62ml container has a pressure of 1.5 atmospheres. Find the new pressure if the container volume is reduced to 51ml.
Pressure x volume = constant. 62 x 1.5 = 93. 93/51 = 1.8 atmospheres (1dp).
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What is the relationship between temperature and pressure?
Pressure is proportional to absolute temperature - If you increase the temperature, you increase the pressure.
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How does temperature affect pressure?
If you increase the temperature of a gas, you give the particles more kinectic energy. This means that the particles are moving faster, causing more collisions with the container walls. This increases the pressure.
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What happens if you double the temperature (in k)?
You double the pressure.
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Give the equation linking pressure and temperature at a constant volume.
Pressure/Temperature(in K) = constant.
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A container has a volume of 30 litres. It is filled with gas at a pressure of 3 bars and a temperature of 217K. Find the new pressure if the temperature is increased to 325K.
(3/217) x 325 = 4.5bars (1dp).
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What is the relationship between temperature and volume?
Temperature is proportional to volume at a constant pressure.
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How does heating up a gas increase its pressure?
If you heat up a gas, you give its particles more kinetic energy. This means they are spread out more.
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What makes up for the lack of collisions?
As the volume is increased, the particles are more spread out meaning less collisions occur. However as the particles have more kinetic energy, the collisions are harder so the pressure remains constant.
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What is the equation linking volume and temperature?
Volume/Temperature (in K) = constant.
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A gas at constant pressure, with a temperature of 270K has a volume of 24 litres. Find the new volume if the temperature is increased to 315K.
(24/270) x 315 = 28 litres.
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What did scientists used to think the Sun did with its energy?
They believed that the Sun just burned its own material to produce energy.
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Why did they realise this wasn't the case?
They realised that the Sun would have needed an impossible amount of fuel to keep it burning for so long.
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What did Einstein discover?
That mass could be converted to energy.
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What is fusion?
The combining of two particles.
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What is nuclear fusion?
Two nuclei can combine to form a larger nucleus.
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What happens in stars?
Hydrogen nuclei fuse to make helium nuclei.
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What happens when two lighter nuclei fuse to make a heavier nucleus?
Energy is released.
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How is nucleus fusion made possible?
The two nuclei need to be brought close together.
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What is needed to bring two nuclei together?
High temperatures and pressures.
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What did Einstein think regarding mass and energy?
That mass is a form of energy, so mass can be converted into other forms of energy.
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What is Einstein's famous equation?
E = mc2.
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What do the letter stand for in this equation?
E = energy released. m= amount of mass lost. c = speed of light in a vacuum.
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What happens when nuclei undergo fusion?
They lose mass and energy is released.
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What do you have to make sure in nuclear equations?
That the numbers balance on both sides.
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What is the atom mass and proton number of a positron?
Atom mass = 0, proton number = 1.
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What is the role of a positron?
To conserve energy.
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Describe the stages in the production of a helium nucleus.
1.Two hydrogen nuclei fuse to form a larger hydrogen nucleus and a positron. 2.A small hydrogen nucleus and a larger hydrogen nucleus fuse together to form a helium nucleus, two hydrogen nuclei and energy.
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What is the heaviest nucleus that can made from fusion?
Iron.
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What do all hot objects emit?
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It is a continuous spectrum of radiation.
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Do hot objects emit the same amount of all radiation?
No they always emit more of one type of radiation than the others.
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What is this type of radiation called?
The peak frequency.
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What does the peak frequency emitted by a hot object depend on?
The object's temperature.
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Compete the sentence. The higher the temperature...
The more energy the photons radiated will have, so the higher the peak frequency.
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What also increases with temperature?
Luminosity.
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How can we tell how hot a star is by looking at it?
A red star = low frequency = a cool star. A blue star = high frequency = hot star.
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What type of star is the sun?
A fairly cool star as it is a yellowy colour.
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What is does an atom contain?
Electrons that move around a tiny nucleus.
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What are the charges of nuclei and electrons?
Nucleus = Positive. Electrons = negative.
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How are electrons arranged?
In energy levels around the nucleus.
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When do electrons move between levels?
When they gain or lose energy.
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What is ionisation?
When electrons gain enough energy to be removed from an atom.
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When are absorption spectra formed? (Part 1)
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When are absorption spectra formed? (Part 2)
Because there are only certain energy levels that an electron can occupy, electrons absorb a particular frequency of radiation to get into a higher energy level.
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When can you 'see' this happening? How?
If a continuous spectrum of visible light shines through a gas. The electrons in the gas atoms absorb certain frequencies of the light, making gaps in the spectrum. These gaps appear as dark lines.
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When are emission spectra formed?
Electrons are unstable in the higher energy levels so they tend to fall from higher to lower levels, losing energy by emitting radiation of a particular frequency. This gives a series of bright lines formed by the emitted frequencies.
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What do astronomers use line spectra to work out?
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What are the energy levels like for different elements?
They are different.
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What does this mean regarding line spectra?
Each element has its own line spectrum.
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What do these line spectra correspond to?
The energies needed for electrons to get from one energy level to another.
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What is the photosphere?
The surface of a star.
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What does the photosphere emit?
A continuous spectrum of radiation. This radiation passes through the gases in a star's atmosphere, which produces emission and absorption lines in the spectrum.
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How can you use a spectrum to identify a chemical?
By looking at the position of the lines in the star's spectrum, you can work out what chemical elements are present in the star's atmosphere by comparing it with a known spectrum in the lab.
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How is a protostar formed?
Stars start off as a cloud of dust and gas - mainly hydrogen and helium. Gravity causes the denser region of the cloud to contract very slowly into clumps. When these clumps get dense enough, the cloud breaks up into protostars.
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How is a main sequence star formed? (Part 1)
The protostar continues to collapse under gravity - reducing in volume. This makes the particles more squashed up, increasing the pressure and temperature. Eventually the temperature at the centre of the protostar reaches a few million degrees.
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How is a main sequence star formed? (Part 2)
The hydrogen nuclei start to fuse together to form helium. This releases an enormous amount of energy and creates an outward pressure to stop the gravitational collapse.
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Which part of the star is the hottest?
The core.
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Where does most of the fusion take place in a star? Why?
In the core. The pressure from the weight of the rest of the star makes the core hotter and denser than the rest of the star. This means the nuclei are close enough together to fuse.
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What happens to the energy that is created by fusion in the core?
It is transported by photons of radiation and convection currents to the photosphere.
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What happens to the energy at the surface of a star?
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Complete the sentence. The more massive the star...
The hotter its core and the heavier the nuclei it can create by fusion.
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When do all stars change?
When there is not enough hydrogen to fuse to make helium.
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What happens when the hydrogen runs out?
The core shrinks, the rest of the star expands and the photosphere cools.
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What happens to small stars next?
They become a Red Giant.
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What happens to the big stars?
They become a Red Supergiant.
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What is happening in a Red Giant and Red Supergiant?
The core is compressed by the surrounding matter of the star and shrinks until the pressure and temperature of the core is high enough for helium fusion to begin. The star releases energy by fusing helium into larger nuclei like carbon, nitrogen+oxy.
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What does a Red Giant become? How? (Part 1)
A Red Giant becomes a White Dwarf. Once there is too little helium to fuse, the core becomes unstable and it's compressed by the rest of the star. A Red Giant doesn't have enough mass to compress the core, so no more nuclear fusion occurs.
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What does a Red Giant become? How? (Part 2)
The outer layers of the star are thrown off into space and the core shrinks to become a hot white dwarf. In white dwarf stars there is no nuclear fusion so the star gradually cools and fades.
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What does a Red Supergiant become? How? (Part 1)
The core turns to mostly iron. A Red Supergiant does have enough mass to increase the pressure and temperature of the core enough to fuse larger nuclei.
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What does a Red Supergiant become? How? (Part 1)
Each time an element in the core becomes depleted, the core shrinks until it is hot enough and at a high enough pressure for further fusion to occur. This happens until most of the core has been fused to make iron.
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What happens now to a big star?
Red Supergiants cannot fuse iron, so the core collapses and the star explodes as a supernova - creating nuclei with masses greater than iron.
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What happens next?
The core collapses to form a neutron star, or if there's enough matter, a black hole from which even light can't escape.
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What is the Hertzsprung-Russell Diagram?
A graph that plots temperature and luminosity of stars.
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How are the stars arranged in this diagram?
Different types of stars are grouped together in distinct areas.
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What do the different areas show you?
The main stages of a star's life cycle: The main sequence, red giants and supergiants and white dwarfs.
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Why can we see these areas?
Stars exist in these stable stages of their life cycle for long periods of time.
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Give an example of an unstable stage.
Supernova.
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Why don't we see unstable stages on the diagram?
Because they happen too quickly.
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What are the advantages of using a computer controlled telescope? (Part 1)
1.The astronomer doesn't always have to be with the telescope, they can just program the telescope to track an object in the sky.
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What are the advantages of using a computer controlled telescope? (Part 2)
2.Computer controlled telescopes can be programmed to constantly repositioned when doing a survey that involves studying large areas of the night sky. 3.They allow telescopes to be positioned more precisely.
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What are the advantages of using a computer controlled telescope? (Part 3)
4.Telescopes can be put in remote places without the astronomer having to travel there to collect the data. 5.Computers can record and process data from telescopes.
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Where do Scientists think the necessary conditions for life are most likely to be found?
On other planets or moons.
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What evidence have they found to suggest there is other life in the universe?
There is evidence for planets orbiting around hundreds of nearby stars.
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What do scientists believe?
Even if only a small proportion of stars have planets orbiting them, there is still a chance of extraterrestrial life.
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Has any evidence been found of extraterrestrial life?
No, so far there's no evidence that any extraterrestrial life exists or has existed in the past.
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What do astronomers need in order to understand what's going on in space?
Accurate measurements.
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Why is this not always possible?
The atmosphere can ruin the results.
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How does the atmosphere do this?
Our atmosphere only lets certain wavelengths of electromagnetic radiation through and blocks all others.
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Which radiation does the atmosphere let through?
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Visible light. Light gets refracted by water in the atmosphere, which blurs the images. It can also be absorbed by the dust particles in the air.
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What is one solution to this problem?
Choosing sites for astronomical observatories on Earth very carefully to try and minimise all of these problems.
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What is another solution?
Using space telescopes.
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What are the advantages of using space telescopes?
1.You can look at the EM radiation that is blocked or affected by the atmosphere. 2.It avoids absorption and refraction affects of light in the atmosphere.
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What are the disadvantages of using space telescopes?
1.They are a lot more expensive to and harder to build, maintain and repair than Earth-based telescopes. 2.Space programmes have uncertainties.
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What are the uncertainties of space programmes? (Part 1)
1.They are extremely expensive. 2.Governments have to balance paying for space programmes with paying for things like defence, healthcare and coping with natural disasters. This means there could be cut-backs at any time.
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What are the uncertainties of space programmes? (Part 2)
3.Many countries space programmes are linked so a cut-back in one country can have a knock-on effect in other countries.
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Where are most of the world's optical and infrared observatories situated?
Hawaii, Chile, Australia and the Canary Islands.
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Why do countries work together in astronomical research?
1.It is too expensive for one country to carry out. 2.You can get the best people and the best facilities for the job.
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Give an example showing how international cooperation is essential for progress in astronomy.
1.The International Space Station is a project led by the US with the help of 15 other countries. Each country is providing different parts of the Station and it's the largest and most expensive international science project in industry.
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Give another example showing how international cooperation is essential for progress in astronomy.
2.The European Extremely Large Telescope is a project involving astronomers from across the whole of Europe, but based in Chile. It's too complex and expensive for a single country to build and operate.
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Describe the astronomical factors that influence the choice of the site for major astronomical observatories. (Part 1)
1.Distant from built up areas that cause light pollution which affects the observations. 2.High elevation to decrease the amount of atmosphere between the observatory and the telescopes to minimise any blurring effects it has.
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Describe the astronomical factors that influence the choice of the site for major astronomical observatories. (Part 2)
3.Low atmospheric pollution and dry air to stop the water in the atmospshere from refracting the light. 4.Frequent cloudless nights so that clouds do not block the view of the telescope.
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Describe the non-astronomical factors that need to be taken into account. (Part 1)
1.Cost - Transporting the materials to remote places is very expensive. There's the cost of building, running and eventually closing the observatory. 2.Access - The site will have to have roads built to it as well as electricity and other facilities.
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Describe the non-astronomical factors that need to be taken into account. (Part 2)
3.Environmental - Scientists have to be careful that building works, etc. will damage the surrounding environment as little as possible, eg. by disturbance to wildlife or agriculture.
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Describe the non-astronomical factors that need to be taken into account. (Part 3)
4.Social - Workers need facilities such as water, electricity, accommodation, shops, etc., which will be quite expensive to provide.
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Explain how some observatories have benefited the local community.
By providing jobs in building and maintaining the observatory.
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## Other cards in this set

### Card 2

#### Front

How long does it take the Moon to orbit the Earth?

28 days.

### Card 3

#### Front

How long does it take the Earth to rotate once on its axis?

### Card 4

#### Front

What is a sidereal day?

### Card 5

#### Front

How long is a sidereal day?

#### Back

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Good flashcards for OCR. You can print these out and cut them into smaller cards and revise using them.

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This is amazing. Thank you so much for uploading- seems to have all the information you need.

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Jheeze - I am going to die tomorrow. I need my Astronomy GCSE to pull through and save me to get that A*.

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this is great, however, card 235 is incorrect, as heavier elements can be fused, in a supernova.

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are the answers for these questions available?

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