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How does the Earth rotate on its axis?
west-east once in just under 24 hours
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How does the Earths' rotation make the stars appear to move?
east-west across the sky once in just under 24 hours
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How do the Sun, planets and moon appear to move? How is their motion and the time they take to cross the sky affected? How does the Sun appear to travel?
East-west across the sky. Affected by their relevant orbits. Across the sky once every 24 hours.
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What is a sidereal day? What is a solar day?
The time it takes for the Earth to rotate 360 degrees on its axis. The time from noon on one day to noon on the next.
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What makes a sidereal day different to a solar day?
Sidereal day is four minutes shorter than a solar day due to the orbiting movement of the Earth (it rotates once on its axis and also orbits the Sun).
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What will the stars seen in the sky from the Earth depend on?
The Earth's position in relation to the Sun's position.
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What can the position of an astronomical object can be measured in terms of/
Angles as seen from the Earth.
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What do the angles of declination and right ascension describe?
The positions of the stars relative to a fixed point on the equator.
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Where is the declination and right ascension measured?
Declination = south and north of the celestial equator. Right Ascension = around the equator.
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Where will a star with a positive/negative declination visible from?
Positive = Northern hemisphere Negative = Southern hemisphere.
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Which planets can be seen from Earth with the naked eye?
Mercury, Venus, Mars, Saturn, Jupiter.
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What makes planets appear differently from stars from Earth?
Because the planets change their positions in complicated patterns when compared to the background of fixed stars.
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How do planets sometimes appear to move relative to the fixed stars?
With retrograde motion.
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How can observations of Venus be used as an example to show how planets change their position?
Venus is closer to Sun than Earth, so it orbits Sun faster than Earth. If Venus is observed over a long enough period of time it can be seen to move compared to background stars.
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Explain how Venus appears to move against background stars.
When Venus is on same side of Sun as Earth, it appears to be travelling in one direction against the background of the stars, yet when it is on the other side, it appears to be travelling in the opposite direction.
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What is retrograde motion?
Where the planets appear to slow down against the star background and go into reverse as the Earth's smaller orbit causes it to overtake each of the other planets at different times of year.
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How does the Moon orbit and what happens due to the orbiting movement?
Orbits Earth in same direction as Earth rotates on its axis. Moon appears to travel east-west across sky in a little over 24 hours.
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What does the lunar cycle describe? What is the Moons shape during its orbit due to?
The moons appearance during its 28 day orbit. The part of the moon visible from earth.
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Why are we able to see the moon?
Because the Suns light is reflected from it - the side of the moon facing towards the sun appears to be light, moon facing away from sun appears dark.
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What faces of the moon are seen from Earth on the moons orbit?
New moon (dark side), waxing cresent, first quarter, waxing gibbous, full moon (light), waning gibbous, third quarter, waning cresent, new moon.
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When does a solar eclipse occur?
When the Moon passes between the earth and the Sun. Can happen during a new moon and results in the Moon casting a shadow on the Earth.
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When does a total solar eclipse occur?
When Moon is directly in front of Sun and completely obscures Earths view of Sun.
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What can the physical implications of observing a solar eclipse be?
If viewed directly, can damage the eye.
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When does a lunar eclipse occur?
When Earth is between Sun and Moon. Results in Earth casting shadow on moon.
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Why don't eclipses occur every month?
Because the Moon doesn't orbit Earth in the same plane as Earth orbits the Sun.
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When can an eclipse only occur?
When Moon passes through the eliptic (the apparent path Sun traces out along the sky). More likely to occur when Moon is to side of Earth rather than between Earth and Sun.
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How frequent are solar eclipses?
2-5 times per year
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How frequent are total eclipses?
Once every 18 months
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What can happen to light, water and sound waves?
Can be refracted or diffracted
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What is refraction?
When waves cross a boundary between one medium and another, the frequency remains the same but there is a change in wavelength. This leads to a change in wave speed, which causes wave to change direction.
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What is diffraction?
When waves more through a narrow gap or past an obstacle, they spread out from edges.
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When is diffraction most obvious?
a) when size of gap is similar to or smaller than wavelength of wave. b) when waves that pass obstacles have long wavelengths.
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What do light waves need in order to be different?
A very small gap
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What does the fact that light and sound can be diffracted provide evidence of?
Their wave nature
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What is radiation diffracted by?
The aperture of a telescope
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How must the aperture be in order to produce sharp images in the telescope.
Must be very much larger than wavelength of radiation detected by telescope
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What happens to white light when it passes through a prism?
Colours that make up white light are refracted by different amounts
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Which colours are refracted the least and the most?
Red = least Violet = most
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Why does the refraction of light in a prism occur?
Because the colours that make up white light have different frequencies and different wavelengths
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What else can be produced when white light passes through a diffraction grating?
A spectrum
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What does a convex lens do?
Bends rays of light inwards as they pass through lens. If rays entering lens are parallel, rays will be brought to a focus at focal point. This is due to refraction.
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How can a lens be more powerful?
If it has a greater curvature
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How can you calculate the power of a lens?
Power (dioptres) = 1/ Focal length (metres)
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What is the focal length?
the distance between the focal point and lens.
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What do ray diagrams show?
How the image of an object would be formed.
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Why do we draw the rays of light entering telescopes as parallel rays?
Because objects in space are so far away that rays of light from them seem to be parallel.
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What is a simple refracting telescope made from?
Two converging lenses of different powers. The eyepiece lens is a higher power lens than the objecture lens.
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What does the objective lens do?
Captures parallel light from a distant object and brings it to a point on the focal point of the lens.
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What is the point on the focal point of the lens also a focal point for? What does this mean?
The eyepiece, so the image acts as an object for the eyepiece, which magnifies it.
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What will the distance between the lenses be equal to?
The sum of the focal lengths of the objective and eyepiece lenses.
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What does an astronomical (reflecting) telescope normally use for the objective lens and why?
A concave mirror as it allows them to be larger, meaning they can collect more light.
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What do concave mirrors do?
Reflect rays of parallel light and bring them to a focus
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What is the effect of a larger telescope?
It captures more light and has more detail visible on the image.
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Why are larger telescopes needed?
To have any chance of seeing any useful details as there will not be much light from distant/faint sources.
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How will the image of a distant magnified object appear? What does this mean?
Image will appear closer than the object,, so the angle made by ray lines entering the eye is greater.
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What is this increase in angle called and what does it do?
Called the angular magnification and makes image appear bigger/closer.
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What is the formula to find the angular magnification of a telescope?
Magnification = Focal length of objective lens/ focal length of eyepiece lens
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What is parallax?
The apparent motion of an object against a background.
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What causes the parallax motion of an object?
The motion of the observer
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What is a simple way to observe parallax?
If you hold your thumb out in front of your eye, when you close aternate eyes your thumb appears to move, in reality you're just looking at it from a different angle.
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How can parallax make a star appear to move?
Make it move in relation to the other stars in the course of a year.
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What causes a star to appear to have moved from Earth?
The movement of the Earth's orbit around the Sun.
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What is the parallax?
Half the angle moved against a background of distant stars in six months
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What will the parallax angle of an object that's further away from the Earth than a closer object?
A smaller parallax angle.
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Why do astronomers use parallax?
To measure interstellar distances using the unit parsec (pc)
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What is the typical interstellar distance between stars?
A few parsecs
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What is a parsec and what is it similar to in size?
Is the distance to a star with a parallax angle of one second of an arc. It is of a similar size to a light year.
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What do astronomers use the megaparsec (Mpc) to measure?
Intergalactic distances even though these objects are so far away that the parallax angle is too small to measure.
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How many parsecs is the nearest major galaxy, Andromeda, away?
770000 or 0.77Mpc
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What is the formula for calculating the distance in parsecs?
Distance (parsecs) = 1/parallax angle (arcseconds)
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How else can astronomers measure the distance to stars?
By observing how bright the stars are?
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What does a stars luminosity depend on?
Its size and temperature
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Which star may emit more light, a hot large star or a cool small one? However what may this mean?
The large hot star. However it may appear brighter even if it's further away.
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What does the observed intensity of a star depend on?
its luminosity and distance from Earth
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What is the luminosity of a cepheid variable star? Why?
it doesn't have a constant luminosity as it pulses and its luminosity depends on the period of pulses.
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What is the period equal to?
1 / frequency of the ulses
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What can this changing frequency be used to work out?
The distance to cepheid variable stars
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What can astronomers estimate by measuring the frequency of the pulses?
The stars luminosity
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What else must be known for the distance to the star to then be worked out?
How bright the star really is and how bright is appears.
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What debate took place and between who in 1920?
The Curtis-Shapley debate about the scale of the universe, between two prominent astronomers Heber Curtis and Harlow Shapley.
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What had telescopes revealed? What did this observation lead to the realisation of?
That the Milky Way contained lots of stars. Led to the realisation that the Sun was a star in the Milky Way galaxy.
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What had telescopes also revealed?
Many fuzzy objects in the nights sky which were originally called nebulae and played a major role in the debate.
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What did Curtis believe?
That the Universe consisted of many galaxies like our own and that the fuzzy objects were distant galaxies.
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What did Shapley believe?
That the Universe contained only one big galaxy and the nebulae were nearby gas clouds within the Milky Way.
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What did Edwin Hubble discover in the mid 1920s?
That a nebula which he had observed containing Cepheid variables, was much further away than any star in the Milky Way.
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What evidence did this observation provide?
That the observed nebula was a separate galaxy, hence supporting Curtis' idea that the Universe contains many different galaxies.
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What have further observations of many cepheid variables allowed astronomers to do?
Measure the distance to these galaxies, and so determine the scale of the universe.
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What else did Hubble discover about the universe when he observed Cepheid variable stars?
That the Universe was expanding, in fact the further away a star was, the faster it was moving away.
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What have Cepheid variable stars in distant galaxies been used to do and why?
To accurately calculate the Hubble constant because we know how far away they are.
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What can we use to find out how fast galaxies are moving away 9what their speed of recession is)?
The red shift.
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What do astronomers now use to calculate the distance to other galaxies?
the hubble constant and red shift data
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What is the formula for calculating the speed of recession?
Speed of recession (km/s) = Hubble constant (s^-1) (km s^-1 Mpc^-1) x Distance (km) (Mpc)
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How do scientists believe the universe began and when?
Began with a huge explosion called the Big Bang about 14000 million years ago
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What indicates that the light from stars in distant galaxies is red shifted?
The spectra observed from the elements in stars.
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The more distant a galaxy...??
The more the light is red shifted.
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What does the motion of the galaxies suggest?
That space itself is expanding
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What are extrasolar planets?
Planets that orbit a star other than the Sun.
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What were the first extrasolar planets to be discovered?
Large gas planets
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What other discoveries have been made since detection methods have become more sensitive?
Smaller planets similar to the size of the Earth.
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Even if a small proportion of stars have planets, what do many scientists believe? However...?
That it is likely that life exists elsewhere in the universe. However no evidence of extraterrestrial life has so far been discovered by scientists.
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What is gas pressure caused by?
Particles in a gas moving about. When a particle collides with an object, it exerts a force which is felt as pressure.
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What does the amount of pressure depend on?
The number of collisions per second and the momentum of the particles.
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What happens to the particles as the volume of a gas is reduced?
The particles have less room to move around so they collide with each other more frequently, increasing the pressure.
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What is the formula for calculating the constant?
Pressure x volume = constant *only true if temp of gas is constant*
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What happens if a gas is heated?
The particles move around faster, which increases their momentum and the force they exert when they collide with each other.
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What are the two effects that could happen if a gas is heated?
The volume and/ or pressure could be increased
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What is the formula for calculating the constant (involving temp and pressure)?
Pressure/ temp = constant *only true if volume is constant*
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What is the formula for calculating the constant (involving temp and volume)?
Volume/temp = constant *only true if pressure is constant*
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For a fixed mass of gas, what are the pressure and volume of gas proportional to?
The absolute temperature
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What happens as the temperature of a gas is reduced?
The particles in the gas move slower and the pressure falls.
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What is absolute zero?
Where the particles in a gas eventually stop moving altogether, at this point they have no more energy to lose and the temp can't get any lower, which occurs at -273 degrees Celcius
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What is absolute temperature a measure of? What is it measured in?
Temperature starting at absoute zero and is measured in Kelvin (K)
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How do you convert Kelvin into degrees Celsius and visa versa?
Kelvin - Celsius = subtract 273 Celsius - kelvin = add 273
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What are the three main parts of a star?
The core (hottest part here nuclear fusion takes place and energetc photons are released). The convection zone (where energy in form of photons is transferred to surface by convection currents). The photosphere (where photons are radiated into space)
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What do stars emit a radiation of?
A range of EM radiation- high luminosity and high peak frequency (i.e. frequency where most energy is emitted)
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What do the luminosity and peak frequency increase with?
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What range does an object that is red hot emit most of its energy?
In the red frequency range.
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What does the frequency of light given off from a star provide evidence of?
How hot it is.
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What is ionisation?
The removal of electrons from an atom
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What does the movement of electrons within the atom cause it to emit?
Radiation of specific frequencies called line spectra.
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What do different elements have?
Characteristic line spectra
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What can we see by comparing a star's spectrum to emission spectra from elements?
Which chemical elements the star contains
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What does the Suns spectrum indicate?
It is complex, indicating it contains more than one element
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What do the absorption lines in the Suns spectrum exactly match?
The emission lines from some elements produced in labatory conditions.
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What do different electron energy levels in atoms give?
Rise to line spectra
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How do electrons move to higher and lower energy levels?
Gain energy to move to a higher energy level and then release light of one wavelength only when they return to the lower energy level.
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How are there series of lines with different wavelengths emitted?
Because there are several possible moves in an atom
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How do stars begin?
As clouds of gas (mainly hydrogen), as gravity brings these gas clouds together they become denser.
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What does the force of gravity do?
Pulls the gas inwards, causing the pressure and temperature to increase. As more gas is drawn in, the force of gravity increases, which compresses the gas so that it becomes hotter and denser, forming a protostar.
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What then eventually happens to the protostar?
The temp and pressure become so high that the hydrogen nuclei fuse into helium nuclei, energy is relased in this nuclear fusion process making the star now a stable main sequence star.
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What do nuclear processes discovered in the early 20th century offer a possible explanation for?
The Suns energy source.
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Where does most of the nucear fusion occur?
In the core of a star, where the temp and density are highest.
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The bigger the star...??
The hotter the core and heavier the nuclei it can create by fusion.
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When is energy freed? What are heavier nuclei made with?
When light nuclei fuse. With masses up to that of the iron nucleus.
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What happens in the core of the Sun?
Hydrogen fuses to form helium.
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What happens to average main sequence stars eventually?
They form red giants
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What happens in the core of a red giant?
The core contracts and its temp rises. Then a further series of fusion occurs: - helium fuses to form carbon - further reactions produce heavier nuclei such as nitrogen and eventually oxygen.
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What happens at each stage of the stages of fusion in a red giant?
Energy is released at each stage.
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When is it possible for no more fusion reactions to occur?
If the mass of the red giant is less than about three times the mass of the Sun.
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What can nuclear fusion produce in a high mass star?
Heavier nuclei up to and including iron.
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What happens when the core is mostly iron?
It explodes as a supernova, creating nuclei with masses greater than iron, producing a dense neutron star or black hole.
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What is produced in the first stage of nuclear fusion when hydrogen nuclei fuse to produce helium nuclei?
A release of energy, also a positively charge particle, a positron, is produced that has the mass of an electron.
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Why must the positron be released?
To balance the charges in the reaction
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What is Einsteins equation E=mc^2 used to calculate?
The energy released during nuclear fusion and fission. E= energy produced m= mass lost c= speed of light in a vacuum
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What is the life cycle of a star?
Path 1= protostar, average main sequence star, red giant, white dwarf. Path 2= protostar, massive main sequence star, red supergiant, supernova, neutron star/ black hole.
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What is the role of the Hertzsprung Russel diagram?
Is a plot of temperature and luminosity and identifies regions where supergiants, red giants, main sequence stars and white dwarfs are located.
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What is the journey of a star like our Sun, as shown by a Hertzsprung Russel diagram?
Sun becomes red giant which lacks mass to compress core further at end of helium fusion. Then shrinks to form white dwarf, where there is no nuclear fusion. White dwarf gradually colls and fades.
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Where are the major optical and infared astronomical observatories on Earth mostly situated?
In Chile, Hawaii, Australia and the Canary Islands.
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What are two examples of these kind of observatories?
Royal Observatory (largest refracting optical telescope in UK) and mauna Kea Observatories (in Hawaii, largest optical reflecting telescopes in world).
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Why has Hawai proven to be an ideal location?
High altitude(less atmosphere to absorb light from distant objects), isolated location (less pollution to interfere with received signal + distance from areas that cause light pollution), equatorial location (best view of solar eclipses).
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What other reason has Hawai proven to be an ideal location?
Frequent cloudless nights.
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What factors should be considered when planning, building, operating or closing down and observatory?
Cost, environmental and social impact nearby, working conditions for employees.
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What can be made much larger than lense in a refracting telescope?
Mirrors for relecting telescopes.
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Why can a mirror have a greater weight without distorting?
As the weight of the mirror is supported underneath rather than on the edges (as the weight of a lens is).
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What can space based telescopes fo? Give an example of a space based telescope.
Obtain images of the Universe that cna't be obtained in any other way. The Hubble telescope.
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What are the advantages of space telescopes?
They avoid absorption and refraction effects of the Earths atmosphere, can use parts of the EM sprectrum that the atmosphere absorbs.
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What are disadvantages of space telescopes?
Very expensive to set up, maintain and repair. Are uncertainties associated with space programmes (e.g. launch delays).
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What are two advantages of controlling a telescope from a computer?
Telescope can be programed to continually track certain objects, data can be collected over long period of time for analysis. Telescope can be situated in an isolated location which may be usually hard to reach, can control remotely.
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What are another two advantages of controlling a telescope from a computer?
Telescope can be programmed to precisely find any star, galaxy or other objects by entering coordinates of object. Computer can directly record and process data collected.
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How are most of the big new telescopes developed?
Through international cooperation.
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What are advantages to international cooperation?
Cost of building telescopes shared, expertise shared, astronomers can book time on telescopes in different countries so can see stars on other sides of Earth.
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What is one observatory that was the result of shared work and between who?
the Gemini Observatory in Chile, shared between Australia and six other countries.
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What does the Great Canary Telescope allow astronomers to do? Who was it funded by?
Capture some of the most distant light in Universe. Mainly funded by Spanish government but Mexico and Uni of Florida also contributed.
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How can telescopes be accessed?
Directly at site, through remote computer control, through Internet.
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Other cards in this set

Card 2


How does the Earths' rotation make the stars appear to move?


east-west across the sky once in just under 24 hours

Card 3


How do the Sun, planets and moon appear to move? How is their motion and the time they take to cross the sky affected? How does the Sun appear to travel?


Preview of the front of card 3

Card 4


What is a sidereal day? What is a solar day?


Preview of the front of card 4

Card 5


What makes a sidereal day different to a solar day?


Preview of the front of card 5
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