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Astronomy Class site: Lecture 6

Join the Physics 1830 lecture on Powers of Ten, Near Earth Objects, and other astronomical topics. Contact the UM Astronomy Club for more information.

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Astronomy Class site: Lecture 6

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  1. Class site: http://www.physics.umanitoba.ca/~english/2015winterphys1830/ Phys 1830: Lecture 6 Password- will change TODAY Add/Drop date TODAY. • If you joined the class late then to register your iclickers email the following: • your iclicker number • your student number • your name Planetarium info mailed to you. Contact Mr. Cameron if you are new. • Previous Class: • Angular Size • Linear measurements (ex. Diameter) Define distance units (AU) • Powers of Ten notation • This Class: • continue with Powers of 10 • Near Earth Objects • Definition of Parsec • Distance via Parallax • Distance via the Inverse Square Brightness Law • Next Classes: • Light and Electromagnetic Radiation • The interaction between atoms and light

  2. Special Club! • Contact: • umastroclub@gmail.com University of Manitoba Astronomy Club Wonder about the origins of the Universe? Curious about black holes? Come out and help design the club activities! No need to be a geek  Today First Meeting Monday Jan 19 at 3pm in Allen 514

  3. Order of Magnitude Example: • Near Earth Objects: http://neo.jpl.nasa.gov/ca/

  4. Order of Magnitude Example: A Near Earth Asteroid from http://neo.jpl.nasa.gov/ca/ -> Close Approaches: On Feb 15, 2013 Asteroid 2012 DA 14 was at its closest approach to Earth. The distance between it and Earth was 0.00019 AU. 1 AU is about 150 million km. For comparison, the moon is about 384,000 km. How many lunar distances (LD) is the asteroid from the Earth?

  5. Compare to diameter Earth: • diamE = 12,756 km ~ 1.3 * 104 km • LD/diamE = 4* 105 km/1.3 * 104 km • LD/diamE = 4/1.3 * 105-4 • LD ~ 30 diamE • Distance between Earth & Moon is “miss” distance == LD. • How big? LD = 384,000 km ~ 4* 105 km

  6. Order of Magnitude Example: A Near Earth Asteroid from http://neo.jpl.nasa.gov/ca/ -> Close Approaches: On Feb 15, 2013 Asteroid 2012 DA 14 was at its closest approach to Earth. The distance between it and Earth was 0.00019 AU. 1 AU is about 150 million km. For comparison, the moon is about 384,000 km. How many lunar distances (LD) is the asteroid from the Earth?

  7. Order of Magnitude Example: == means “defines” ~ == approximately 3. Convert the Earth-asteroid distance from AU to km: Collect together co-efficients, then collect together the powers of 10, then the units. • Round off the value of the distance between Earth and the asteroid: e.g. 0.00019 AU ~ 0.0002 AU • Convert to powers of 10: and Note the power of ten rules! See the external links/supplemental page on the class website.

  8. Order of Magnitude Example: 4. Round off the value of the distance between Earth and the moon: 384,000 km ~ 400,000 km 5. Convert to powers of 10:

  9. Order of Magnitude Example: 6. Form the ratio of the asteroid-earth distance/moon-earth distance : Distance to asteroid --------------------------- = Distance to moon • Now can answer the question: How many lunar distances (LD) is the asteroid from the Earth?

  10.  == “gives” • So this asteroid was between Earth & moon! • Since 1/10 = 0.1 • And rounding up 0.075 ~ 0.08 which is slightly less than 0.1. •  the asteroid is < 1/10 of LD (== lunar distance). • Note there are 30 earth diameters in 1 LD.

  11. Another Comparison: Distance to asteroid compared to diameter of Earth. Earth radius = 6371 km Earth diameter = 2 * Earth radius = 12742 km ⁄ ⁄ ⁄ ⁄ • About 2 earth diameters away from the centre of the Earth.

  12. Worried about the math? -- OPUS (Organization of Physics Undergraduate Students) can tutor! Find them on the tunnel level of the Allen Physics Building. -- Tutors available (talk to Dr. English) -- Dr. English’s office hours 3pm Monday, Allen 514 • Doing this sort of question is • to easy • o.k. for me • way too hard

  13. Order of Magnitude Review Question: DO AS PRACTISE On Sept 21, 2009 Asteroid 2009 SK15 was at its closest approach to Earth. The distance between it and Earth will be 0.0194 AU. 1 AU is about 150 million km. For comparison the moon is about 384,000 km. How many lunar distances is the asteroid from the Earth? Pick the closest answer. • Greater than 100 lunar distances. • Less than 10 lunar distances but beyond the orbit of the moon. • Greater than 5 lunar distances but closer than the orbit of the moon. • 0.8 lunar distances and thus closer than the moon is to the Earth.

  14. Press Release: http://www.jpl.nasa.gov/news/news.php?release=2015-015 An asteroid, designated 2004 BL86, will safely pass about three times the distance of Earth to the moon on January 26. (~1.2 million kilometers) from Earth.) "I may grab my favorite binoculars and give it a shot myself," said Yeomans. "Asteroids are something special. Not only did asteroids provide Earth with the building blocks of life and much of its water, but in the future, they will become valuable resources for mineral ores and other vital natural resources. They will also become the fueling stops for humanity as we continue to explore our solar system. There is something about asteroids that makes me want to look up." • NASA Near Earth Objects • http://neo.jpl.nasa.gov/ca/ • Exercise: • do for Apophis Jan 9th and in 2036.

  15. Distances to Stars: • Parallax Effect: • Hold your thumb just in front of your nose. • Close your right eye while keeping your left eye open. • Note where your thumb is relative to the shapes above. • Switch eyes and note where your thumb is relative to the shapes above.

  16. Distances to Stars: Parallax • Use the radius of the Earth’s orbit over a 6 month period. • Measure the angle of the arc between the position of a star in January and the position in July.

  17. Distances to Stars: Parallax • Parsec definition: • The distance that an object would have if its parallax is 1 arcsec. • Written “pc”.

  18. Distances to Stars: Parallax 1 pc = = 3.26 ly = 206265 AU 1 kpc = 1 kiloparsec = 1 Mpc = 1 megaparsec =

  19. Review Question: If a star is further away from us will its parallax angle be larger or smaller? (Hint: Test with your thumb.) • Larger • smaller

  20. Review Question: Star X is known to be 10 pc from us and Star Y is 50 pc away. Which star has the greatest parallactic angle? • Star X • Star Y • Neither – their parallactic angle is the same

  21. Distances: Less than 24 years. Greater than 32,000 years At least 24,000 years. Less than 8,000 years. Our Sun is about 8 kpc from the centre of our Milky Way Galaxy. How long does it take light from the centre of the Milky Way to reach us? Select the best answer. (Recall, 1pc = 3.26 ly)

  22. Parallax measured by the European Space Agency’s (ESA) HIPPARCOS satellite Interesting Public Outreach Image using parallax: The Hyades in 3-D: defocus your eyes on the 2 most right images or use a mirror on all 3 to get a 3-D stereo view. More at http://www.rssd.esa.int/index.php?project=HIPPARCOS&page=stereo • HIPPARCOS measured • precise positions, parallaxes and motions • 2.5 million stars in 3.5 years • Out to about 200 pc • could have measured the diameter of a human hair at a distance of 20 kilometres. • Movie of the Hyades Cluster of stars: http://www.rssd.esa.int/SA-general/Projects/Hipparcos/movies/hyades.mpg

  23. Distances to Stars Too Distant for Parallax Currently parallax  distances out to < 1000 pc • Gaia: • 10**9 stars over 5 yrs • 10 kpc! • 400 000 times fainter than eye • positions to an accuracy of 24 microarcseconds • A distant star is a point source. (The apparent size is due to lenses in the telescope spreading out the light of bright stars.) • The energy per second output in all directions by a star is its luminosity. This is constant.

  24. Distances to Stars Too Distant for Parallax • As radiation moves away from a point source it becomes diluted. • Notice how much its apparent brightness changes with the radius of the sphere, i.e. distance.

  25. Distances to Stars Too Distant for Parallax Inverse Square Brightness Law

  26. Review Question: Star X and Star Y have identical characteristics. Seen from Earth Star X appears brighter than Star Y. Therefore Star X is closer to Earth. • True • False

  27. Review Question: Star X is at a distance of 1 ly and Star Y is at a distance of 5 ly. (Both appear as points.) The luminosity from Star X is diluted over the area of 1 square. How many squares and which apparent brightness is correct for Star Y. • 5 squares and 1/5 times the apparent brightness of Star X. • 25 squares and 1/25 times the apparent brightness of Star X. • 25 squares and 25 times the apparent brightness of Star X. • 5 squares and 1/25 times the apparent brightness of Star X.

  28. Distances to Stars Too Distant for Parallax == light curve == spectrum How do we know that certain stars share the same luminosity? • Examine how their light varies with time: e.g. Variable stars, Supernovae • Examine how their light varies with wavelength: e.g. if they have the same properties in blue light through red light.

  29. Distances to Stars Too Distant for Parallax

  30. Next Topics: Electromagnetic Radiation • Wave and particle models of light • Colour and temperature • Interaction of light with matter • Spectra • Motion and Doppler Shift

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