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# P7 Observing space

ocr 21st century p7 unit 2012 edit
by

## Pete Davis

on 8 December 2015

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#### Transcript of P7 Observing space

P7 Observing the universe Solar and Sideral Day Solar and lunar eclipse A solor day is the time it takes
for the sun to appear in the
same position in the sky It last 24 hours A sideral day is the time for the Earyth to rotate once It's measured against
background stars It lasts 23 hours 56 minutes Lunar Eclipse Sun - Earth - Moon Solar Eclipse Sun - Moon - Earth Motion of the stars and planets Retrograde motion happens
with the outer planets, it happens
because both the planet and Earth are moving. Cepheid Variable Star's Pulse in Brightness A Parsec is the distance of a star
when the Parallax angle
is 1 Arc Second The moon's orbit is inclined to the Earth's so eclipses are uncommon The moon orbits the Earth every 27.3 days (sideral month) Beyond 50 pc angle to small to be precise Apparent Brightness (alias INTENSITY) = how much light reaches Earth
Intrinsic Brightness (alias LUMINOSITY) = total amount of light a star emits

Apparent Brightness depends upon Intrinsic Brightness & Distance The luminosity of a star depends on its temperature and size Distance (parsec) = 1/Parallax angle (arcsec) 1 Parsec = 3.26 lightyear A light year is 9,460,730,472,580.8 km or
about 6 Trillion miles or the distance travelled by light in a year refracting

telescopes Draw This ! Measure in dioptre Measure in metres (not cm!) Reflecting telescopes diffraction Where do you put telescopes ? More curved lens have shorter focal length Skinny Objective Curvy eye You have 20 seconds
to complete the
last drawing Skinny lens Curvy lens Magnification = Fo Fe Greatest when aperture
is same size as wavelength In a telescope the aperature (the objective lens)
must be bigger than the wavelength

objective Lens sag
imperfections
chromatic aberration Problems with Refractors Draw this ! Advantage
where do you
put the eyepiece ? The apperature needs to be wide for faint sources Avoid Light Pollution Avoid the atmosphere Difficult to build
and maintain Difficult conditions
for astromoners One solution is using remote control with computers Advantages
Scan large areas
track objects
Coordinate telescopes
all around the world Summary
days
eclipses
movement of planets
Parallax
intrinsic brightness
cephied variables
reflecting telescopes
refracting telescopes
observatories Spectra and temperature stellar evolution absolute zero Atoms and the Sun the Rutherford-Marsden-Geiger gold foil experiment
Nuclear Fusion
The structure of the Sun Gold foil experiment Hubble Red shift The further away the galaxy the greater the red shift !

The furthest galaxies are receding at the greatest velocity. P7.4 The Sun, the stars and their surroundings

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

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

3. know 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. Be able to 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. Be able to interpret absolute zero using a molecular model and kinetic theory

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

10. Be able to use the relationships:

a) pressure × volume = constant

b) pressure / temperature = constant

c) volume / temperature = constant

11. Be able to 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. HT only: 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. know that the more massive the star, the hotter its core and the heavier the nuclei it can create by fusion

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

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

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

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