V Spring 2012 Astronomy CourseMississippi Valley Night Sky ConservationThe Night Sky Around Us

Program developed byMississippi Valley Conservation AuthorityRoyal Astronomical Society of CanadaOttawa Astronomy Friends

Instructors:Pat BrowneStephen CollieRick ScholesCourse Assistant:Amy Booth

Earth Centered Universe software for illustrations – courtesy David Lane

Announcements:

1. Donated set-screw to FLO

2. Transit of Venus courtesy Rick

3. Lab time/Observing after

http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/lec17.html

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.

As we continue, peering deeper and deeper into space,we climb the distance ladder to find star cluster distances, galaxy distances and beyond

Night Sky V - Observable Cosmic distances

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 parsecDefinition of parallax arc-sec - parsec:http://www.youtube.com/watch?v=6zV3JEjLoyE&feature=relmfu

  

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

Tan(p) = AU / d

d

First Rung - Distance Ladder Rung 1 Estimating Distance to Nearby Star - Parallax

1 AU (astronomical unit) = Sun-Earth

Nearby stars have proper motion when measured against the more distant background stars For relatively nearby stars we use Trigonometric Parallax p

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 Cephei

http://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

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://vger.pa.msu.edu/posters/M3M5Talk.pdf

http://astro.unl.edu/naap/distance/cepheids.html

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.

Astronomical Procedure: From Apparent Magnitudes of Variable Stars to their Distances

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.

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

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

The longer the period, the more luminous the Cepheid

Distance From Known Distances in our Galaxy

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.

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

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 – 5D = antilog ((m -M + 5)/5)

Distance Modulus

M m

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

Distance to LMC – Simple Calculation based in Cepheids within the Milky Way

For this example, based on Cepheids within the Milky Way apparent magnitude: 15.57Absolute Magnitude: -3.6

We can derive the distance d = 10 ^(m - M + 5)d = 10 ^(15.57 - (-3.6) + 5)/5d = 10^ 24.17/5d = 10 ^4.834d = 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 manyCepheids as possible in another galaxy in order to determine

amore accurate distance. As the number of stars observed go

upthe uncertainties involved in calculations for individual stars can be statistically reduced. http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_cepheids.html

WHERE Locating Galaxies by star-hoppingObserving individual island Universes (poetic

term)Observing interacting galaxiesObserving 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)

V Night Sky Around UsBeyond the Milky Way, The Realm of the Galaxies

M65.M66

M64

M51M51 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)

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)

M66

M65

http://www.asod.info/?p=1759 astronomy sketch of the day – Getting a Black Eye in Coma Berenices

NGC 3628 hides its spiral structure because we see it edge-onThe dust lane here is very prominent.

of Galaxies

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)

Clusters

https://community.emc.com/people/ble/blog/2012/02/28/space-is-flat-what-does-it-mean

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

The Ultimate Spectral Distance Ladder

Question Raised: What is cosmological redshift ?It is the spectral shift in wavelength due to the velocity ofthe space-time fabric between the observer and the distant object (galaxy). It is a measurement of the recession velocity – a velocitythat is not intrinsic to the motion of the object, but dueto the fact that the universe is expanding according toHubble’s Law:Recessional Velocity = Hubble's constant times distanceV = Ho D

In cosmological redshift, the wavelength at which the

radiation is originally emitted is (only) lengthened as ittravels 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!

Night Sky V - Extreme Cosmic distances

Then… as the telescope looks outward the realm of thesuperclusters 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. 56Richard Preston

Quasi-Stellar Objects Quasars – Deeply Red-shifted Luminous objects At first it wasn't understood what these objects were, since their spectra were unlikethose 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 wenow know quasars to be — extremely luminous objects at cosmological distances.

“Maarten Schmidt found an object among the most distant galaxiesthat burned with a terrifying light”.

First Light, The Search for the Edge of the Universeby Richard Prestonp. 174

The clock or the computer is finiteTo 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 OrbitThe 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

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!

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

The Night Sky around us … tonight

Compare May Sky to Early April…

New objects to observe, new place in our orbit…

Planisphere

Observing Plan May 11 2012 - Western Sky then Towards the Meridian South

Start with the things that aregoing 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

M44

M67

Mars

Coma Star Cloud

M84,M86

M65,66

M64

M53

M3

M51

M104Saturn

eta Virginis

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…

Observing Plan May 11 2012 - Towards the East (ushering summer in)

M13M92

http://www.asod.info/?p=5946

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

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/group/MoK_NSC/

Some feedback…

• What helped you most in understanding the NightSky material?

• What suggestions would you like to make?