Allan Sandage, one of the 20th century's most influential cosmologists, once described cosmology as "a search for two numbers". One of these, the Hubble constant, has recently become the subject of a large debate in the astronomical community. In this talk I'll go over the history of measurements of the Hubble constant and the evolution of its measured value over time. We'll end with a discussion on the recent discrepancies which have arisen between local and late-time measurements of this parameter.

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Hi all,

We’ll be having our first organizational meeting of the Meeting of Astrophysics Students at Stanford (MASS) tomorrow at 12:30 pm. We’ll be deciding on the topics we want to discuss and a rough schedule for presentations (with a particular focus on incorporating the interests of the undergraduate summer students we have with us this quarter).

Numerical simulations and calculations are creating an increasingly complete picture of the universe. We think we have a good idea of the content of galaxies and the mechanisms that form them. Given that we expect galaxies to form from hierarchical mergers and that most galaxies have SMBHs at their cores we may be interested in the dynamics of the SMBHs following merging.

When we talk about the science we can extract from the CMB, we often focus on the the imprint of the standard lambda CDM parameters on the power spectrum. However, as these CMB photons have carved a path through the universe, they’ve picked up subtle imprints of the clusters of galaxies in their path. Two of these effects – thermal and kinetic Sunyaev–Zeldovich effects – offer probes of the universe’s largest scale structure all the way to the time when the CMB was first formed.

Gaia is a revolutionary instrument that has given us positions and proper motions of local stars to precisions that are frankly ridiculous. One especially exciting application of this data for the cosmologically inclined amongst us is a deeper understanding of the  substructure in the Milky Way.

Line-intensity mapping—the observation of aggregate emission in various atomic and molecular spectral lines—is an emerging technique with tremendous potential to shed light on how the first stars and galaxies formed, as well as on subsequent early-universe star formation and galaxy formation.

The Event Horizon Telescope is a network of roughly ten telescopes spanning nearly the entire earth.  By operating the telescope as an interferometer, the EHT is able to image with roughly ten microarcsecond resolution.  This puts it in a position to view the event horizons of two black holes, Messier 87, and Sagitarius A*, the black hole in the center of our own galaxy.  But they do not just take a simple photograph of the event horizon with a big camera.  Oh no, t

The next generation of dark-energy imaging surveys – so called “Stage-IV” surveys, such as that of the Large Synoptic Survey Telescope (LSST) – will cross a threshold in  the  number  density  of  detected  galaxies  on  the  sky  that  requires  qualitatively  different image analysis and measurement techniques compared to the current generation of Stage-III surveys.