Discoveries 1917 100” Hooker telescope on Mt. Wilson 1920 “Debate on the Scale of the Universe” Interpreta on of the “Spiral Nebulae” Harlow Shapley “only gas clouds” within a single galac c Universe Sun far from the center Heber Cur s Sun at the center of our rela vely small galaxy all the spiral nebulae are other galaxies Measure the size – HOW??
Fall 2018 1 Yardstck 1.Brightness (magnitude)
2.Parallax
3.Cepheid Variables
November 23, 1924 Edwin Hubble, 35, published in the New York Times his discovery that there were many galaxies further away from the Milky Way.
Fall 2018 2 MilkyMilky Way 18381838 Discovery of stellar parallax Discovery of stellar parallax (F.Bessel) )
11 1 Parsec = Parsec = = = 3.263.26 ly P (arcsec) (arcsec)
11 Mpc = 10= 106 parsecs = 3.26 million lightyears parsecs = 3.26 million lightyears
FallFall 2018 2018 213 Cepheid Variables At Harvard (Society For the Collegiate Instruc on of Women) Oberlin and Radcliff Colleges she was cap vated by Astronomy.
Variable stars vary periodically in brightness
Henrie a Leavi Henrie a found ~50) Cepheid variables
Fall 2018 4 Edwin Hubble ! Confirmed the extra galac c nature of nebulae using Cepheid variable yards ck
! Observed that every galaxy appears to be moving away from every other one
Farthest ones moving faster
Fall 2018 5 Velocit measurement
Doppler Effect
A er Einstein
Fall 2018 6 Speed vs. Distance
Fall 2018 7 Hubble Constant
Not constant!
Fall 2018 8 What is going on? Q1 Moving away? – the track back and find where they started
Finally Copernicus is verified – we are not at the center of the Solar system – we are not at the center of the Galaxy – we are not at the center of the Universe Q2 Where are they going? For a me it was thought that Gravity would pull it all together
Fall 2018 9 Technical Advances
200 in Hale telescope Hubble Space Telescope Palomar Observatory
Fall 2018 10 Cosmological Principle
! Space is homogenous ! Space is isotropic
Looks the same from any posi on
Fall 2018 11 Deep Field
No stars in our galaxy Deep field (north) Deep field (south)
Homogeneity is observed on scales large compared to distances between galaxies
Fall 2018 12 Geomety
-1 0 1 2 3 4
Distance between them (equal spacing)
Elas c string Distance depends on me
Fall 2018 13 Geomety-2
expansion
Fall 2018 14