The Milky Way in optical - look at all the dust.



Herschel had the idea that he could could the number of stars in each direction to work out where the center of the galaxy was.




The dust got in the way and his map looked like this:




But in the halo there are globular clusters. Shapley used these plus the RR Lyrae P-L relation to obtain the distance to them and hence the size of the galaxy.




In I-R we can see into the center of the galaxy. Wavelength of IR and radio emission > size of dust particles.









This is what the Milky Way looks like edge on.




Contains spiral arms that were detected in radio




The Milky way face on.




This is how the arms rotate.




This is if it were a solid disk (record player, frisbee etc)




This is Kepler's law. Reality somewhere inbetween




The rotation curves of the arms imply dark matter!




The very center of the galaxy can be seen in radio.




Zoom in




further




the motion of the stars close in imply a black hole at the center of the galaxy. At least 10^6 M sun.




First picture of a galaxy other than our own.




What look like nowadays




Zoom in on the cepheid variables. The P-L relation revealed they were at great distances and hence not part of our own galaxy.




P-L relation for RR Lyraes and Cepheids. Standard candles. From P get L, measure b get d.




Supernova Type Ia also standard candles - obtain the distance scale.




Spiral galaxies - arms less wound a - c - appear blue star formation




Barred spirals




Elipticals - appear red, little star formation.




Globular cluster - small galaxy




Lenticular galaxies - like S's but no arms.




Irregular - the LMC




Hubble deep field - all splodges are galaxies




Milky way is a spiral. They are generally found in groups or in the field. We are in a group with the Andromeda galaxy, M31.




A cluster contains E's




The Coma cluster




The APM survey




and the CfA survey - showed that all galaxies are clusters but E's more so than S's.




Interactions between galaxies happen




Famous HST picture of the Antenna galaxy.









Our galaxies rotation curve implies dark matter. Same for other galaxies.




Lens from massive galaxies




and also from clusters. Mass of galaxies < mass from lensing => more dark matter.




Doppler shift seen in galaxies.




Hubble plotted distance against recession velocity. Found the Universe was expanding!




The galaxies themselves do not expand - just the space inbetween