An age difference of two billion years between a metal-rich and a metal-poor globular cluster.

Globular clusters trace the formation history of the spheroidal components of our Galaxy and other galaxies, which represent the bulk of star formation over the history of the Universe. The clusters exhibit a range of metallicities (abundances of elements heavier than helium), with metal-poor clusters dominating the stellar halo of the Galaxy, and higher-metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and were later engulfed along with their original host galaxies, and which were formed within it.

A tidally distorted dwarf galaxy near NGC 4449.

NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8 megaparsecs (ref. 3).

Preparing your organization's training program for ICD-10.

Training for ICD-10 is going to be expensive, though predictions of how expensive vary widely. Healthcare finance executives should create a flexible, multiyear capital and operating budget to prepare for ICD-10 conversion and the training and support that will be required. Healthcare organizations also should assess staff knowledge in the critical ICD-10 areas and begin training now to be ready for go-live by early 2013.

An ancient nova shell around the dwarf nova Z Camelopardalis.

Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter, by way of an accretion disk, to its white dwarf companion. In dwarf novae, an instability is believed to episodically dump much of the accretion disk onto the white dwarf. The liberation of gravitational potential energy then brightens these systems by up to 100-fold every few weeks or months.

Probing the faintest stars in a globular star cluster.

NGC 6397 is the second closest globular star cluster to the Sun. Using 5 days of time on the Hubble Space Telescope, we have constructed an ultradeep color-magnitude diagram for this cluster. We see a clear truncation in each of its two major stellar sequences.