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

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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 P
at 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

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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/note
s/lec17.html
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First Rung - Distance Ladder Rung 1 Estimating
Distance to Nearby Star - Parallax
Star measured 2 different points and times of Earth Orbit   Point 1 Earth is on one side of the Sun Point 2 ( 6 Months) Opposite Side. The nearby star appears to shift its position, relative to more distant stars, because we are viewing it along two slightly different lines of sight. Based on http//www.astro.gla.ac.uk/users/martin/ase/runaway_ase.htm
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
Parallax angle and using the Astronomical Unit Distance 1 AU / Tan(p) No more than a few arc secs (or 1/3600 degs) Distance 1 / theta ( very small angle) For p of 1 arc sec, this distance corresponds to 206,265 AUs or 3.26 light years (63,115 aus/ly) (This is the definition of the parsec? Definition of parallax arc-sec - parsec http//www.youtube.com/watch?v6zV3JEjLoyEfeaturerelmfu

  
                                                                                     
Illustration of the effect of stellar parallax.  Between Julyand January the apparent position of the nearby star shiftswith respect to the more distant background stars.
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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
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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

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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
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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.
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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.u
k/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?projectHIP
PARCOSpageastrometry
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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.
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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
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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

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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

http//outreach.atnf.csiro.au/education/senior/ast
rophysics/variable_cepheids.html
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V Night Sky Around UsBeyond the Milky Way, The
Realm of the Galaxies

• 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

M51
M51 Whirlpool Galaxy
BlackEye Calaxy M64
M64
M65.M66
Leo Triplet
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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/?p1759 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/?p1699 (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
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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
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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.o
  rg/wiki/Type_Ia_supernova

See also http//www.astro.gla.ac.uk/users/martin/a
se/runaway_ase.htm http//www.bautforum.com/showt
hread.php/38030-Supernova-in-M100-Spiral-Galaxy?s
5c7d93be72c3a684d130139fe3fd9513
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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
• Hubbles 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!

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Night Sky V - Extreme Cosmic distances

• Then as the telescope looks outward the realm of
  the
• superclusters stretches into unmapped deserts of
  timeAs 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

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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
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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
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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

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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!

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Lab Exercise April 13 2012 Western Sky has changed since then Constellation Celestial Object

Taurus M1 Crab Nebula

Taurus M45 Pleiades

Gemini M35

Auriga M37
Auriga M36
Auriga M38

Orion M42
M43
M78
Puppis (not Monoceros) M47
M46
Cancer M44 Beehive
Cancer M67 2700 6.1 30

Leo M65 - Leo Triplet
M66
Canes Venatici M3 - Globular Cluster 33900 6.2 18
M51 - Whirlpool Galaxy 37000000 8.4 11x7
Ursa Major M81 12000000 6.9 21x10 
Ursa Major M82 - peculiar galaxy 12000000 8.4 9x4
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The Night Sky around us tonight

• Compare May Sky to Early April
• New objects to observe, new place in our orbit

Planisphere
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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
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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

M13
M92
http//www.asod.info/?p5946
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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

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The Night Sky Around Us Night Sky Friends
Conserving the NightSky by sharing it Welcome
to the universe of friends that never ends
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NightSky Friends http//tech.groups.yahoo.com/grou
p/MoK_NSC/
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Some feedback

• What helped you most in understanding the
  NightSky material?
• What suggestions would you like to make?