The Distance Scale Ladder Determining Astronomical Distances Determine

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The Distance Scale Ladder

The Distance Scale Ladder

Determining Astronomical Distances Determine the AU (see handout) l Wait 150 years l First

Determining Astronomical Distances Determine the AU (see handout) l Wait 150 years l First parallax done in 1839 (1/3 asec) l Stars are now known to be light years away l What New Problem is suddenly created with this discovery?

Problems with Parallax Measurements Atmospheric motions limit position measurement precision of a single set

Problems with Parallax Measurements Atmospheric motions limit position measurement precision of a single set of measurements l Have to average position measurements over about 20 years to get reliable parallax l Systematic error could be present (and indeed it is) l

D = 15 Parsecs D = 25 Parsecs This feature Not Real

D = 15 Parsecs D = 25 Parsecs This feature Not Real

Hipparrcos Satellite Data 100, 000 stars

Hipparrcos Satellite Data 100, 000 stars

Luminosity Scale of the MS is determined from stellar parallax

Luminosity Scale of the MS is determined from stellar parallax

So Any systematic error in parallax leads to systematic error in the main sequence

So Any systematic error in parallax leads to systematic error in the main sequence l Systematic error in luminosity scale of main sequence leads to systematic error in measuring distances to clusters l

Cluster Distances Stars are all at the same distance l Clusters contain Cepheid Variables

Cluster Distances Stars are all at the same distance l Clusters contain Cepheid Variables l

Cepheid Variables Long Period variables are very bright l Individual ones can be seen

Cepheid Variables Long Period variables are very bright l Individual ones can be seen in nearby galaxies l Can be used to determine Galaxy distances l Hubble Space Telescope greatly extends the range of distances out to which Cepheids are observed l

Cepheid Calibration of Tully Fisher Relation

Cepheid Calibration of Tully Fisher Relation

Tully Fisher Relation n n Can be extended to very large distance because galaxy

Tully Fisher Relation n n Can be extended to very large distance because galaxy rotational velocities are easy to measure Can reach the undisturbed Hubble flow to measure the true expansion parameter. All systematic errors accumulate to this point Expansion parameter tells us expansion age

Scale Scale Factor Scale Drawings Scale Scale FactorScale Scale Factor Scale Drawings Scale Scale Factor
Extragalactic distances Introduction The distance ladder Gravitational lensesExtragalactic distances Introduction The distance ladder Gravitational lenses
DISTANCE LEARNING DISTANCE LEARNING Distance education or distanceDISTANCE LEARNING DISTANCE LEARNING Distance education or distance
Astronomical Units of distance Astronomical units a uAstronomical Units of distance Astronomical units a u
SCALE LIMITED SCALE RC SCALE 10 SCALE 20SCALE LIMITED SCALE RC SCALE 10 SCALE 20
Chapter 20 Galaxies Determining Distance Measuring distances toChapter 20 Galaxies Determining Distance Measuring distances to
Distance Metric Common Properties of a Distance DistancesDistance Metric Common Properties of a Distance Distances
Scale Drawings Models Scale Drawings Models l DistancesScale Drawings Models Scale Drawings Models l Distances
Cosmic distance 201482174 Cosmic distance ladder The cosmicCosmic distance 201482174 Cosmic distance ladder The cosmic
Sight Distances Sight Distances The safe and efficientSight Distances Sight Distances The safe and efficient
Distances extragalactiques Introduction Lchelle des distances Mirages gravitationnelsDistances extragalactiques Introduction Lchelle des distances Mirages gravitationnels