Astronomers have leapt on Hot Paper #4 because it accompanies the second release of data to the public, on March 15, 2004. This release has positions and imaging data from one-twelfth of the sky, scooping 88 million objects, along with more than a third of a million spectra of galaxies, quasars, and stars. The survey is accompanied by a marvelous array of common user tools for teasing out data in a multitude of ways. For example, in this release there are spectra of 35,000 stars in the Milky Way. For this sample we now have stellar radial with an accuracy of ~5 km/s, and these can be used for modeling stellar motions in the Galaxy.

The exciting results from the SDSS include the discovery of distant quasars seen when the universe was just 900 million years old; the definitive measurement of the large-scale distribution of galaxies, confirming the role of gravity in growing structures in the universe; and evidence that the Milky Way grew by cannibalizing smaller galaxies.

The triumph of this SDSS paper will, however, be brief, like a new comet blazing in the sky. The third data release occurred on September 27, 2004, and the fourth release has recently occurred. In the fourth survey researchers will find 673,280 spectra: 480,000 galaxies, 64,000 quasars, and 89,000 stars, a doubling of the data set in paper #4. These data will be invaluable for kinematical studies of the Galaxy and its halo because the dataset on bright F-type stars (a standard candle for distance measurement) is greatly increased, and the sample includes objects out on the periphery of the halo. The next data release is slated for mid-2007. Then a survey to refine our knowledge of the structure and makeup of the Milky Way will keep SDSS busy until the summer of 2008.

Meanwhile, the aging Hubble Space Telescope (HST) is still a world-class facility, as paper #8 reminds us. This is a further contribution to the determination of the cosmological parameters (#1, #2, and #7). Adam Riess (Space Telescope Science Institute, Baltimore) and his colleagues have made it their business to recover the past history of the expanding universe by observing distant supernovas. Paper #8 describes the discovery of 16 Type Ia supernovas, 6 of which are the highest redshift supernovas discovered. Distance is important in the cosmology game, because the more distant the standard candle, the earlier the epoch we can learn about.

In reducing the data, Riess and his colleagues re-analyzed the light curves of 170 supernovas, and added the 16 HST objects to the sample, because these extend the investigation deeper into space, and therefore further back in time. A simple kinematic explanation of the data on magnitude and velocity favors a universe with a recent acceleration and a past deceleration. In other words, the universe has experienced a transition from deceleration in the past to the acceleration we experience today, which appears to be propelled by dark energy.