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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 – PowerPoint PPT presentation

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

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

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
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
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.
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
Distance Ladder Rung 2 Variable Stars
example Delta Cepheihttp//en.wikipedia.org/wiki/
  • 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

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).
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.
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.
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
The longer the period, the more luminous the
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
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.
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.
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
Other Variables confirm distances to the LMC and
  • The distance to the LMC practical
  • Different methods to measure the distance to the
  • 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
  • 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

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

V Night Sky Around UsBeyond the Milky Way, The
Realm of the Galaxies
  • Locating Galaxies by star-hopping
  • Observing individual island Universes (poetic
  • 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

M51 Whirlpool Galaxy
BlackEye Calaxy M64
Leo Triplet
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)
NGC 3628 hides its spiral structure because we
see it edge-on The dust lane here is very
of Galaxies
  • Past the Milky Way to other systems with
  • of stars
  • As we dart away from our home galaxy at many
  • times the speed of light to get to the next
  • of galaxies in the constellations of Virgo and
  • 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
  • space, sharing the same destiny
  • (Deep Sky Objects, David Levy, p 188)

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

See also http//www.astro.gla.ac.uk/users/martin/a
se/runaway_ase.htm http//www.bautforum.com/showt
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
  • distant object (galaxy).
  • It is a measurement of the recession velocity a
  • 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
  • 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
  • and not from the motion of the object. So the
  • velocity is not the galaxies motion, but the
    motion of
  • space-time. This is a very special spectral shift

Night Sky V - Extreme Cosmic distances
  • Then as the telescope looks outward the realm of
  • 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

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
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
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
  • 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
  • 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

Tools for Lab Exercises
  • Observing Exercises http//www.millstonenews.
  • Software programs ECU, Stellarium, Sky Safari
  • Celestial Sphere 3D and Planisphere 2D Visual
  • 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

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
Puppis (not Monoceros) M47
Cancer M44 Beehive
Cancer M67 2700 6.1 30

Leo M65 - Leo Triplet
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
The Night Sky around us tonight
  • Compare May Sky to Early April
  • New objects to observe, new place in our orbit

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
Coma Star Cloud
eta Virginis
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

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

The Night Sky Around Us Night Sky Friends
Conserving the NightSky by sharing it Welcome
to the universe of friends that never ends
NightSky Friends http//tech.groups.yahoo.com/grou
Some feedback
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  • What suggestions would you like to make?
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