P7: Studying the Universe

June 2013 P7 exam walkthrough video

Past papers

June 2013 P7 (Higher)
June 2013 P7 (Foundation)

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Spec points in bold relate to the higher tier only (students doing foundation exams do not need to study these).


P7.1: Naked eye astronomy

1. recall that the Sun appears to travel east-west across the sky once every 24 hours, that the stars appear to travel east-west across the sky once in a very slightly shorter time period, and that the Moon appears to travel east-west across the sky once in a slightly longer time period

2. explain why a sidereal day, a rotation of 360° of the Earth, is different from a solar day due to the orbital movement of the Earth and that a sidereal day is 4 minutes less than a solar day

3. understand that the planets Mercury, Venus, Mars, Jupiter and Saturn can be seen with the naked-eye and that all the planets appear to move with the stars but also to change their position relative to the fixed stars

4. explain the apparent motions of the Sun, stars, Moon and planets in terms of rotation of the Earth and the orbits of the Earth, Moon and planets

5. explain the phases of the Moon in terms of the relative positions of the Sun, Moon and Earth

6. explain both solar and lunar eclipses in terms of the positions of the Sun and Moon and explain the low frequency of eclipses in terms of the relative tilt of the orbits of the Moon about the Earth and the Earth about the Sun

7. explain why different stars are seen in the night sky at different times of the year, in terms of the movement of the Earth round the Sun

8. recall that, and explain why, planets sometimes appear to move with retrograde motion relative to the ‘fixed’ stars

9. understand that the positions of astronomical objects are described in terms of two angles (e.g. right ascension and declination) and understand how the angles relate to the celestial sphere.


P7.2: Light, telescopes and images

1. understand that the speed of waves is affected by the medium they are travelling through and that the wave speed will change if a wave moves from one medium into another

2. understand that a change in the speed of a wave causes a change in wavelength since the frequency of the waves cannot change, and that this may cause a change in direction

3. understand that the refraction of light waves can be explained by a change in their speed when they pass into a different medium

4. describe how refraction leads to the formation of an image by a convex/converging lens

5. understand and draw diagrams to show how convex/converging lenses bring parallel light to a focus

6. draw and interpret ray diagrams for convex/converging lenses gathering light from distant point sources (stars), off the principal axis of the lens and extended sources (planets or moons in our solar system, galaxies)

7. understand that a lens with a more curved surface is more powerful than a lens with a less curved surface made of the same material

8. calculate the power of a lens from:

\mbox{power (dioptres)} = \frac{1}{\mbox{focal length}} \mbox{(metres^{-1})}

9. understand that astronomical objects are so distant that light from them reaches the Earth as effectively parallel sets of rays

10. recall that a simple optical telescope has two converging lenses of different powers, with the more powerful lens as the eyepiece

11. understand that a telescope has two optical elements:
a. an objective lens or mirror to collect light from the object being observed and form an image of it
b. an eyepiece which produces a magnified image of the image from the objective that we can view

12. calculate the angular magnification of a telescope from the powers of the two lenses using:

\mbox{magnification} = \frac{\mbox{focal length of objective lens}}{\mbox{focal length of eyepiece lens}}

13. explain why most astronomical telescopes have concave mirrors, not converging lenses, as their objectives

14. understand how concave mirrors bring a parallel beam of light to a focus

15. explain why large telescopes are needed to collect the weak radiation from faint or very distant sources

16. recall that waves can spread out from a narrow gap and that this is called diffraction

17. draw and interpret diagrams showing wave diffraction through gaps

18. recall that light can be diffracted, and that the effect is most noticeable when light travels through a very small gap, comparable to the wavelength of the wave

19. understand that radiation is diffracted by the aperture of a telescope, and that the aperture must be very much larger than the wavelength of the radiation detected by the telescope to produce sharp images

20. explain how a spectrum can be produced by refraction in a prism

21. recall that a spectrum can be produced by a diffraction grating.


P7.3: Mapping the Universe

1. explain how parallax makes closer stars seem to move relative to more distant ones over the course of a year

2. define the parallax angle of a star as half the angle moved against a background of very distant stars in 6 months

3. understand that a smaller parallax angle means that the star is further away

4. define a parsec (pc) as the distance to a star with a parallax angle of one second of arc

5. calculate distances in parsecs for simple parallax angles expressed as fractions of a second of arc

6. recall that a parsec is similar in magnitude to a light-year and is the unit used by astronomers to measure distance

7. recall that typical interstellar distances are a few parsecs

8. recall that the luminosity of a star depends on its temperature and its size

9. explain qualitatively why the observed intensity of light from a star (as seen on Earth) depends on the star’s luminosity and its distance from Earth

10. recall that Cepheid variable stars pulse in brightness, with a period related to their luminosity

11. recall that and explain qualitatively how this relationship enables astronomers to estimate the distance to Cepheid variable stars

12. understand the role of observations of Cepheid variable stars in establishing the scale of the Universe and the nature of most spiral nebulae as distant galaxies

13. recall that telescopes revealed that the Milky Way consists of millions of stars and led to the realisation that the Sun was a star in the Milky Way galaxy

14. recall that telescopes revealed the existence of many fuzzy objects in the night sky, and that these were originally called nebulae

15. recall the main issue in the Curtis-Shapley debate: whether spiral nebulae were objects within the Milky Way or separate galaxies outside it

16. recall that Hubble’s observations of Cepheid variables in one spiral nebula indicated that it was much further away than any star in the Milky Way, and so he concluded that this nebula was a separate galaxy

17. recall that intergalactic distances are typically measured in megaparsecs (Mpc)

18. recall that data on Cepheid variable stars in distant galaxies has given better values of the Hubble constant

19. use the following equation to calculate, given appropriate data, the speed of recession of a distant galaxy, the Hubble constant or the distance to the galaxy:

\mbox{speed of recession (km/s)} = \mbox{Hubble constant (s^{-1})} \times \mbox{distance (km)}

\mbox{speed of recession (km/s)} = \mbox{Hubble constant (km/s per Mpc)} \times \mbox{distance (Mpc)}

20. understand how the motions of galaxies suggests that space itself is expanding

21. recall that scientists believe the Universe began with a ‘big bang’ about 14 thousand million years ago.


P7.4: The Sun, the stars and their surroundings

1. recall that all hot objects (including stars) emit a continuous range of electromagnetic radiation, whose luminosity and peak frequency increases with temperature

2. recall that the removal of electrons from atoms is called ionisation and explain how electron energy levels within atoms give rise to line spectra

3. recall that specific spectral lines in the spectrum of a star provide evidence of the chemical elements present in it

4. use data on the spectrum of a star, together with data on the line spectra of elements, to identify elements present in it

5. understand that the volume of a gas is inversely proportional to its pressure at a constant temperature and explain this using a molecular model

6. explain why the pressure and volume of a gas vary with temperature using a molecular model

7. understand that both the pressure and the volume of a gas are proportional to the absolute temperature

8. interpret absolute zero using a molecular model and kinetic theory

9. recall that –273°C is the absolute zero of temperature, and convert temperatures in K to temperatures in °C (and vice versa)

10. use the relationships:
a. \mbox{pressure} \times \mbox{volume} = \mbox{constant}
b. \frac{\mbox{pressure}}{\mbox{temperature}} = \mbox{constant}
c. \frac{\mbox{volume}}{\mbox{temperature}} = \mbox{constant}

11. explain the formation of a protostar in terms of the effects of gravity on a cloud of gas, which is mostly hydrogen and helium

12. understand that as the cloud of gas collapses its temperature increases, and relate this to the volume, pressure and behaviour of particles in a protostar

13. understand that nuclear processes discovered in the early 20th Century provided a possible explanation of the Sun’s energy source

14. understand that, if brought close enough together, hydrogen nuclei can fuse into helium nuclei releasing energy, and that this is called nuclear fusion

15. complete and interpret nuclear equations relating to fusion in stars to include the emission of positrons to conserve charge

16. understand that energy is liberated when light nuclei fuse to make heavier nuclei with masses up to that of the iron nucleus

17. understand that Einstein’s equation E = mc2 is used to calculate the energy released during nuclear fusion and fission (where E is the energy produced, m is the mass lost and c is the speed of light in a vacuum)

18. recall that the more massive the star, the hotter its core and the heavier the nuclei it can create by fusion

19. recall that the core (centre) of a star is where the temperature and density are highest and where most nuclear fusion takes place

20. understand that energy is transported from core to surface by photons of radiation and by convection

21. recall that energy is radiated into space from the star’s surface (photosphere)

22. recall that the Hertzsprung-Russell diagram is a plot of temperature and luminosity and identify regions on the graph where supergiants, giants, main sequence and white dwarf stars are located

23. recall that in a main sequence star, hydrogen fusion to helium takes place in the core

24. recall that a star leaves the main sequence when its core hydrogen runs out; it swells to become a red giant or supergiant and its photosphere cools

25. recall that in a red giant or supergiant star, helium nuclei fuse to make carbon, followed by further reactions that produce heavier nuclei such as nitrogen and oxygen

26. recall that a low-mass star (similar to the Sun) becomes a red giant, which lacks the mass to compress the core further at the end of helium fusion; it then shrinks to form a white dwarf

27. recall that in a white dwarf star there is no nuclear fusion; the star gradually cools and fades

28. recall that in a high-mass star (several times the mass of the Sun) nuclear fusion can produce heavier nuclei up to and including iron; when the core is mostly iron, it explodes as a supernova creating nuclei with masses greater than iron and leaving a dense neutron star or a black hole.

29. understand that astronomers have found convincing evidence of planets around hundreds of nearby stars

30. understand that, if even a small proportion of stars have planets, many scientists think that it is likely that life exists elsewhere in the Universe

31. recall that no evidence of extraterrestrial life (at present or in the past) has so far been detected.


P7.5: The astronomy community

1. recall that major optical and infrared astronomical observatories on Earth are mostly situated in Chile, Hawaii, Australia and the Canary Islands

2. describe factors that influence the choice of site for major astronomical observatories including:
a. high elevation
b. frequent cloudless nights
c. low atmospheric pollution and dry air
d. sufficient distance from built up areas that cause light pollution

3. describe ways in which astronomers work with local or remote telescopes

4. explain the advantages of computer control of telescopes including:
a. being able to work remotely
b. continuous tracking of objects
c. more precise positioning of the telescope
d. computer recording and processing of data collected

5. explain the main advantages and disadvantages of using telescopes outside the Earth’s atmosphere including:
a. avoids absorption and refraction effects of atmosphere
b. can use parts of electromagnetic spectrum that the atmosphere absorbs
c. cost of setting up, maintaining and repairing
d. uncertainties of space programme

6. understand the reasons for international collaboration in astronomical research in terms of economy and pooling of expertise

7. describe two examples showing how international cooperation is essential for progress in astronomy

8. understand that non-astronomical factors are important considerations in planning, building, operating, and closing down an observatory including:
a. cost
b. environmental and social impact near the observatory
c. working conditions for employees.