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Centre of Mass

Centre of Mass. Exercise: Where would be the CM of the sun-earth system? Mass of the sun: 2 × 10 30 kg Mass of the earth: 6 × 10 24 kg Would it be close to the centre of the earth, or that of the sun, or somewhere in between?. Common Centre of Mass.

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Centre of Mass

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  1. Centre of Mass • Exercise: Where would be the CM of the sun-earth system? • Mass of the sun: 2 × 1030 kg • Mass of the earth: 6 × 1024 kg • Would it be close to the centre of the earth, or that of the sun, or somewhere in between?

  2. Common Centre of Mass • We must also remember that the earth and the sun must revolve round their common centre of mass. We are used to considering only the earth revolving round the sun.

  3. Two stars move about their common CM CM For animation, visit http://upload.wikimedia.org/wikipedia/commons/7/73/Orbit1.gif

  4. Centre of Mass of the Sun – Earth System • If the centre of mass of the sun-earth system lies close to the centre of the sun (only 449 km away from the centre of the sun of radius 696000 km), what is the implication?

  5. CM of the Sun-Earth SystemNotice slight displacement from the centre of the sun. Earth Sun Based on zebu.uregon.edu

  6. Doppler Shift • Illustration of Doppler Shift Source: http://www.astrosociety.org/education/publications/tnl/67/music.html

  7. Doppler Shift • Notice that the spectral lines shift towards red when the object is moving away from us, and towards blue when it moves towards us. Source of Fig. spheroid.wordpress.com/2007/02/18/astro-seminar-finding-exoplanets/

  8. Wobble of a star The star wobbles because of the presence of a planet. What we see is the shift in the spectral lines from the star. For animation, visit www.astronomynotes.com/lifezone/star-wobble.gif

  9. Motion of the Sun seen from Outside • If alien astronomers began tracking the motion of the Sun in the year 2000, viewing it from its North Ecliptic Pole, this is what they would see over the next 50 years, adjusted for the normal motions of the star and system.

  10. Wobble of the sun For animation of the wobbling motion, visit: http://plus.maths.org/issue10/news/planet/wobble.gif Credit: The New York Times

  11. Velocity Curve of a Wobbling Star • 51 Peg is a variable star Source: www.seti.org

  12. Estimate of the Mass • Once the time period of the wobbling motion is determined, then Kepler’s third law is used to get the combined mass of the star and the planet.

  13. Extrasolar Planets • More than 150 extrasolar planets have been discovered. Most of them have masses similar to that of Jupiter. Technology not yet sufficiently advanced to detect planets of the size of the earth.

  14. Prerequisite for Life to Exist • In order to be able to say whether life exists outside our solar system, it is necessary not only to find planets of the size of the earth, but also to detect molecules which form the basis of life.

  15. Complex Molecules Discovered • Astronomers have found the first signature of complex organic molecules in the dust cloud around a distant star, suggesting that these building blocks of life may be a common feature of planetary systems.

  16. Tholins • In our solar system, the large carbon molecules, called tholins, have been found in comets and on Saturn's moon, Titan, giving its atmosphere a red tinge.

  17. Titan, A Moon of Saturn A picture of Titan from The Hubble Space Telescope, the orange is caused by a thick atmosphere.

  18. Precursors to Biomolecules • Tholins are thought to be precursors to the biomolecules that make up living organisms on Earth (though they are no longer found on our planet because the oxygen in our atmosphere would quickly destroy them).

  19. Detection of Tholins • A new study, reported recently, features observations of the spectrum of the dust disk surrounding the star HR4796A that indicate the presence of tholins there.

  20. Habitable Zone • For life to exist on a palnet, it must also be in the habitable zone. This is the region in the solar system which is neither too hot nor too cold, but just right. Astronomers believe that in other solar systems, too, such habitable zones exist and life is more probable in those planets which fall in this zone.

  21. Habitable Zone in the Solar System 0.95 – 1.37 AU 1 AU is the distance of Earth from The Sun. Fig from www.dur.ac.uk

  22. Habitable Zones • But the habitable zone may be larger than originally conceived. The strong gravitational pull caused by large planets may produce enough energy to sufficiently heat the cores of orbiting moons. Life has proven itself tough here on Earth. Perhaps it could thrive in more extreme environments.

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