The Cosmic Distance LadderThe Cosmic Distance Ladder

Distance Measurements via ParallaxDistance Measurements via Parallax

Hipparcos Satellite Before LaunchHipparcos Satellite Before Launch

GAIA GAIA –– A Planned Future MissionA Planned Future Mission

Estimating the Distance to Estimating the Distance to a Stop Lighta Stop Light

Cepheid Variable StarsCepheid Variable Stars

The PeriodThe Period--Luminosity Relation for Luminosity Relation for Cepheid Variable StarsCepheid Variable Stars

Henrietta Leavitt

HST Observations of Cepheid HST Observations of Cepheid Variable Stars in M100 at ~ 20 MpcVariable Stars in M100 at ~ 20 Mpc

HST key project measured Cepheid distances to ~ 25 galaxies within 25 Mpc.

Distances from Type 1a SupernovaeDistances from Type 1a Supernovae

Mass Discovery of Type 1a SupernovaeMass Discovery of Type 1a Supernovae

Light Curves of Type 1a Light Curves of Type 1a SupernovaeSupernovae

Peak luminosity and subsequent fading are related.

SNAP SNAP –– A Planned Mission toA Planned Mission toMeasure Distances to Type 1a Measure Distances to Type 1a

SupernovaeSupernovae