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V Spring 2012 Astronomy Course Mississippi Valley Night Sky Conservation The Night Sky Around Us

V Spring 2012 Astronomy Course Mississippi Valley Night Sky Conservation The Night Sky Around Us. Program developed by Mississippi Valley Conservation Authority Royal Astronomical Society of Canada Ottawa Astronomy Friends Instructors: Pat Browne Stephen Collie Rick Scholes

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V Spring 2012 Astronomy Course Mississippi Valley Night Sky Conservation The Night Sky Around Us

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  1. V Spring 2012 Astronomy CourseMississippi Valley Night Sky ConservationThe Night Sky Around Us Program developed by Mississippi Valley Conservation Authority Royal Astronomical Society of Canada Ottawa Astronomy Friends Instructors: Pat Browne Stephen Collie Rick Scholes Course Assistant: Amy Booth Earth Centered Universe software for illustrations – courtesy David Lane • Announcements: • Donated set-screw to FLO • Transit of Venus courtesy Rick • Lab time/Observing after

  2. Night Sky V - Observable Cosmic distances As we continue, peering deeper and deeper into space,we climb the distance ladder to find star cluster distances, galaxy distances and beyond Astronomers speak of a distance ladder Each rung gives a leg-up to the next indirect way to determine distances Most indirect methods use the idea of a "standard candle", i.e. something that you believe you know how luminous it is and you can determine its distance by measuring its brightness. Examples: White Dwarf Supernovae, Globular Clusters distributions, The Tip of the Red Giant Branch, Surface Brightness Fluctuations. http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/lec17.html

  3. First Rung - Distance Ladder Rung 1 Estimating Distance to Nearby Star - Parallax Nearby stars have proper motion when measured against the more distant background stars For relatively nearby stars we use Trigonometric Parallax p d 1 AU (astronomical unit) = Sun-Earth Tan(p) = AU / d

  4. Historically and Currently Speaking… Transit of Venus June 5/6, 2012 Transit of Venus expeditions: Using Venus parallax angle we can get distance to the Sun (1 AU) Astronomers mounted expeditions at 2 different locations to determine parallax angle of Venus against the Sun… Only possible when a Transit of Venus occurs…

  5. Distance Ladder Rung 2 Variable Stars example Delta Cepheihttp://en.wikipedia.org/wiki/Delta_Cephei • Cepheid Variables are giant stars that pulsate with a regular periodicity 1-50 days • Mechanism: Outer atmospheres puff outwards, making them larger and brighter, then cool off and fall back, making them fainter. • Progenitor Star – Delta Cepheii

  6. Distance Ladder – Rung 2Cepheid Variable Stars in Star Clusters Cepheids are found in open clusters, globular clusters, and nearby galaxies. Here we see a study of Cepheids in globular cluster M3 (40,000 lys distance). http://astro.unl.edu/naap/distance/cepheids.html http://vger.pa.msu.edu/posters/M3M5Talk.pdf

  7. Astronomical Procedure: From Apparent Magnitudes of Variable Stars to their Distances Plot apparent magnitude values from observations at different times results in a light curve for a Cepheid in the Large Magellic Clouds – our closest extra-galactic neighbour.Henrietta Leavitt did just that. http://upload.wikimedia.org/wikipedia/commons/b/ba/1777_Variables_in_the_Magellanic_Clouds_Henrietta_Swan_Leavitt.png She discovered a simple relation between the brightness of LMC Cepheid variables and their periods ... Since the variables are probably at nearly the same distance from the Earth, their periods are apparently associated with their actual emission of light, as determined by their mass, density, and surface brightness The actual emission or luminousity is a direct measurement of absolute magnitude.

  8. Next Rung – Beyond Globular Clusters – Magallenic Clouds Discovery of the Period-Luminosity Relation was extremely important for measuring distances   It meant that, by measuring the pulsation period of certain Cepheid variable star, one could deduce its luminosity from the Period-Luminosity relation, and thus determine its distance from its apparent brightness. http://www.astro.gla.ac.uk/users/martin/ase/runaway_ase.htm The longer the period, the more luminous the Cepheid Note: Using the Hipparcos Space Mission data which has done measurements (parallax angles with miliarcsec precision), we can ‘truth’ the closer Cepheids by this astrometric reference. See What is astrometry – Hipparcos site http://www.rssd.esa.int/index.php?project=HIPPARCOS&page=astrometry

  9. Distance From Known Distances in our Galaxy Question: How far away is the Large Magellanic Cloud? If we don't know that, we can't convert the relative distances to absolute distances in parsecs. The LMC distance needs to be established from Cepheids within our galaxy. http://spiff.rit.edu/classes/phys240/lectures/lmc/lmc.html We can use the main-sequence fitting technique to compare more distant open clusters to nearby open clusters, and thereby determine further distances. This eventually leads to Cepheid distances within the clusters contained in the LMC. Hence we climb up the next rung of the distance ladder. We have different Cepheids and other variables to choose from to confirm these indirect measurements.

  10. Distance Modulus Given Apparent Magnitude and calibrated measurements of Absolute MagnitudeDistances to Unknown Clusters are Calibrated Distance Modulus: apparent – Absolute = f(D) m-M = m – M = f(Distance in pc). Here the best fit m – M = 5.5 m – M = 5 log d – 5 D = antilog ((m -M + 5)/5) M m

  11. Other Variables… confirm distances to the LMC and Beyond. The distance to the LMC – practical considerations Different methods to measure the distance to the LMC, • RR Lyrae stars are another class of pulsating variable stars. They are much fainter than Cepheids, and much more common. Bright enough that we can see them easily in the Magellanic Clouds, and in a few other members of the Local Group – not so beyond that • Cluster Main sequence fitting, as described , compares the color-magnitude diagram of stars in clusters. Good News : Star clusters in the LMC; the bad news is that the stars in them have a somewhat different chemical composition than stars in the Milky Way. • Eclipsing binary stars in the LMC. By combining measurements of their light, as the stars eclipse each other, with measurements of their radial velocities, as they move in their orbits, we can calculate the distance to such systems. It is necessary to use theoretical models of stellar atmospheres in the process, however, which lends some significant uncertainty to the resulting distance. • Tip of the Red Giant Branch (TRGB) Stars at a certain point in their lives evolve in the color-magnitude diagram to a particular point, which appears to have roughly the same luminosity for almost all stars. Many of these stars are close enough

  12. Distance to LMC – Simple Calculation based in Cepheids within the Milky Way For this example, based on Cepheids within the Milky Way apparent magnitude: 15.57 Absolute Magnitude: -3.6 We can derive the distance d = 10 ^(m - M + 5) d = 10 ^(15.57 - (-3.6) + 5)/5 d = 10^ 24.17/5 d = 10 ^4.834 d = 68,230 parsecs This means that the Cepheid in the LMC is about 68.2 kpc (or about 222,000 light years away). Since the Cepheids as a group are at relatively the same distance this is the derived distance to the LMC As mentioned, astronomers try and observe as many Cepheids as possible in another galaxy in order to determine a more accurate distance. As the number of stars observed go up the uncertainties involved in calculations for individual stars can be statistically reduced. http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_cepheids.html

  13. V Night Sky Around UsBeyond the Milky Way, The Realm of the Galaxies M51 M51 Whirlpool Galaxy WHERE Locating Galaxies by star-hopping Observing individual island Universes (poetic term) Observing interacting galaxies Observing clusters of galaxies (Virgo) WHEN Are they Visible? Spring time ! – We are pointing out towards the NGP (North Galactic Pole, located in Coma Berenices) WHAT Types of Galaxies (Face on, Edge on, Elliptical, Spiral, Barred Spiral, Irregular, Peculiar) – depends on our viewpoint and their intrinsic geometry WHERE: > 2 Million Light Years beyond the Milky Way Famous Examples: • M64 – Blackeye Galaxy - Spiral • M51 – Whirlpool Galaxy - Interacting • Virgo Cluster of Galaxies – Our Local Group • M65,M66 (and NGC 3628) – The Leo Triplet, M65, face on, M66 Edge On) BlackEye Calaxy M64 M64 M65.M66 Leo Triplet

  14. Fanciful Descriptions … BlackEye Galaxy M64 is brighter than 10 billion suns (luminousity). However this depends on our distance estimate. Estimates of 10 to 40 Million Light Years are used for M64. Black band is dust which obscures part of the nucleus of the galaxy. (Turn Left at Orion,Consolmagno and Davis) M64- long black cloud stretches across its face. Its dust lane is raw material that someday will be part of stars and planets, and just as long-gone dust clouds within our own galaxy are now a part of you, dear reader, and me. (Deep Sky Objects, Levy) http://www.asod.info/?p=1759 astronomy sketch of the day – Getting a Black Eye in Coma Berenices Leo Triplet: Messier 66 is part of a really delightful trio of galaxies, of which M65 and NGC 3628 are the other members. While M65 is almost edge-on in appearance, M66 is angles so that we see more of its face, including one spiral arm that hangs more limply than the other, as if the galaxy had suffered some cosmic fall that injured its shoulder – David Levy, p. 193 http://www.asod.info/?p=1699 (image asod – Dale Holt) M65 NGC 3628 hides its spiral structure because we see it edge-on The dust lane here is very prominent. M66

  15. of Galaxies Clusters Past the Milky Way… to other systems with billions of stars… As we dart away from our home galaxy at many times the speed of light to get to the next cluster of galaxies in the constellations of Virgo and Coma Berenices, we travel some 50 million light years As we reach the galaxies of Virgo and Coma Berenices, we realize that our Local Group is bound to this cluster – thousands of galaxies are sharing the same part of space, sharing the same destiny… (Deep Sky Objects, David Levy, p 188) https://community.emc.com/people/ble/blog/2012/02/28/space-is-flat-what-does-it-mean

  16. Standard Candles in other Galaxies Just as we use Cepheid Variables to gauge distances in and around our galaxy, we use Supernova Type 1a beacons found in other galaxies to obtain absolute Magnitude Measurements. Extra-galactic Standard candle - a particular type of exploding star known as a type Ia Supernova.  These objects are  thought to occur in binary systems when a white dwarf star, orbiting around a red giant companion from which it is "gobbling up" matter because of its strong gravitational pull, is pushed over the limiting mass which such a white dwarf star is allowed to have: the Chandrasekhar Limit, about 1.4 times the mass of the Sun.  When this limiting mass is exceeded, it causes a violent thermonuclear explosion, which releases a huge amount of energy - making the type Ia supernova an extremely luminous object. Moreover, since the explosion always happens once the Chandrasekhar Limit has been exceeded, the luminosity of all type Ia supernovae is remarkably consistent - making them excellent standard candles. http://en.wikipedia.org/wiki/Type_Ia_supernova See also http://www.astro.gla.ac.uk/users/martin/ase/runaway_ase.htm http://www.bautforum.com/showthread.php/38030-Supernova-in-M100-Spiral-Galaxy?s=5c7d93be72c3a684d130139fe3fd9513

  17. The Ultimate Spectral Distance Ladder Question Raised: What is cosmological redshift ? It is the spectral shift in wavelength due to the velocity of the space-time fabric between the observer and the distant object (galaxy). It is a measurement of the recession velocity – a velocity that is not intrinsic to the motion of the object, but due to the fact that the universe is expanding according to Hubble’s Law: Recessional Velocity = Hubble's constant times distance V = Ho D In cosmological redshift, the wavelength at which the radiation is originally emitted is (only) lengthened as it travels through (expanding) space. A Cosmological redshift results from the expansion of space itself and not from the motion of the object. So the recessional velocity is not the galaxies motion, but the motion of space-time. This is a very special spectral shift indeed!

  18. Night Sky V - Extreme Cosmic distances Then… as the telescope looks outward the realm of the superclusters stretches into unmapped deserts of time…As a telescope looks backward into time (or out into space) the galaxies appear smaller and fainter. When a telescope probes about 5 billion light years into look-back time, it can detect only the brightest galaxies, giant, elliptical galaxies – because spiral galaxies similar to the Milky Way are too dim to be seen at that distance First Light, The Search for the Edge of the Universe, p. 56 Richard Preston

  19. Quasi-Stellar Objects Quasars – Deeply Red-shifted Luminous objects At first it wasn't understood what these objects were, since their spectra were unlike those of any known stars. Its spectrum did not resemble that of any normal stars with typical stellar elements. 3C 273 was the first object to be identified as what we now know quasars to be — extremely luminous objects at cosmological distances. “Maarten Schmidt found an object among the most distant galaxies that burned with a terrifying light”. First Light, The Search for the Edge of the Universe by Richard Preston p. 174

  20. The clock or the computer is finite To know it is to exhaust its potential for exciting wonder. The night sky is more like a human being, inexhaustibly complex and finally beyond reach. Chet Raymo 365 Starry nights, Introduction

  21. Night Sky Around Us – Putting it All Together • Sun is a Star – Day and Night • When/why can we see something • Where can we see it depends on our place on Celestial Sphere our point in Earths Orbit The Solar System and our own satellite, the Moon – First Quarter Observing • Secrets of Stars – Stellar behaviour from Stellar Spectra • History of Stars - Stellar evolution • Types of Stars Binary Stars, Variable Stars, Red Giants, White Dwarfs, ‘Planetay Nebula’, Supernovae (we are stardust) • Catalogues of Celestial Objects – Messier, NGC • Open Clusters and Stellar Nursuries, Emission Nebula, Reflection Nebula • Globular Clusters – OLD stars – Back to pre-history! • Distance Ladder – Absolute Magnitude and the Distance Modulus • Cepheid Variables in our Galaxy and Beyond… • Extreme Cosmic Distances, and yet we can see quasar 3c273 near eta Virginis1

  22. Tools for Lab Exercises • Observing Exercises: http://www.millstonenews.com/the-night-sky/ • Software programs: ECU, Stellarium, Sky Safari • Celestial Sphere 3D and Planisphere 2D Visual aids • Using Star Charts – Pocket Sky Atlas, Sky Atlas 2000, Deep Map 600 • Observing Tools – Types of telescopes – reflectors, refractors • Types of mounts - equatorial, dobsonian, alt-azimuth • Types of aids - clock drive, go-to • Resources • Gros Merci to MVC for providing the laboratory space!

  23. The Night Sky around us … tonight Compare May Sky to Early April… New objects to observe, new place in our orbit… Planisphere

  24. Observing Plan May 11 2012 - Western Sky then Towards the Meridian South Start with the things that are going to set first Planisphere does not record the planets because they change from year to year. Constellation Object ---------------- --------- Cancer M44 Beehive Cluster , Open Cluster M67 faint Open Cluster Leo Planet Mars (no longer on the meridian) Leo Triplet Galaxies M65,M66… Corvus M104 Sombrero Galaxy (dust lane) Virgo Virgo Galaxies M86,M84 Planet Saturn Quasar 3c273 (near eta Virginis) Coma Berenecies Melotte 111Great Star Cloud(OC) M53 Glocular Cluster M64 Black Eye galaxyCanes Venatici M3 M51 Whirlpool Galaxies M51 M3 Coma Star Cloud M44 M64 Mars M65,66 M53 M67 M84,M86 eta Virginis Saturn M104

  25. Observing Plan May 11 2012 - Towards the East (ushering summer in) Eastern Sky: Constellation Object ------------------- ------------------ Hercules M13- Great Hercules Globular M92 compare and contrast Ursa Major M81,M82 (peculiar galaxy) Lyra Epsilon Lyrae - Double Double M57 – Ring Nebula (planetary nebula) the Cosmic Cheerio… M92 M13 http://www.asod.info/?p=5946

  26. Final Assignment • From this Messier medley, you can identify all of the objects you saw tonight see http://messier.seds.org/ • Write your observations in your astronomy log book

  27. The Night Sky Around Us … Night Sky Friends … Conserving the NightSky by sharing it … Welcome to the universe of friends that never ends…

  28. NightSky Friends http://tech.groups.yahoo.com/group/MoK_NSC/

  29. Some feedback… • What helped you most in understanding the NightSky material? • What suggestions would you like to make?

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