January 6 COVER NASA Spitzer Space Telescope false-color image of a portion of the Perseus spiral arm of the Milky Way. Bright regions are clusters of newly formed stars. Recent observations with the National Radio Astronomy Observatory Very Long Baseline Array yielded the distance to a newly formed star (in the bright cluster toward the lower left) with unprecedented accuracy and precisely located the Perseus spiral arm. See page 54. Image: C. E. Woodward, G. Ruch, T. J. Jones

January 20 COVER A newt lung cell in culture at an intermediate stage of mitotic spindle formation, when most of the chromosomes have already connected to spindle microtubules emanating from the centrosomes but have not yet congressed to the spindle equator. Immunofluorescence highlights -tubulin (green), -tubulin (magenta), and keratin (red). See page 388. Image: A. Khodjakov

January 27 COVER A composite image of marine fish and invertebrate development from egg through late larval stages. As marine organisms grow beyond the egg stage, they become capable of swimming, first vertically for tens of meters, then horizontally for hundreds to thousands of meters. These behaviors influence how far they disperse. See page 522. Image: C. Guigand

February 3 COVER The structure of the hepatitis C virus NS5A-5B natural substrate (yellow), bound to the active site of the NS3-4A protease (blue), has formed the basis for designing novel protease inhibitors that directly interfere with replication of this virus. This image shows the shallow, solvent-exposed binding groove of the NS3-4A enzyme. The Gordon Research Conference on Medicinal Chemistry will be held from 6 to 11 August 2006 at Colby Sawyer College, New London, NH. The schedules for the 2006 Gordon Research Conferences begin on page 676. Image: James Griffith

February 10 COVER Clarkia breweri, a California annual, is a small plant that is pollinated by hawkmoths. Its intensely scented flowers synthesize more than 10 different volatile compounds. As discussed in the special section in this issue, this plant is one of several used
for the study of the volatile chemicals produced by plants for communication and defense. See page 803. Image: David Bay and Eran Pichersky

February 17 COVER Schematic view of Uranus and its rings and inner moons. Recent Hubble Space Telescope images revealed the wide, tenuous outer two rings and several tiny moons. The planet itself is shown in approximately real color. Small moons are shown as sequences of colored dots that represent their orbital motion. See page 973. Image: M. R. Showalter

March 3 COVER The enzymes that catalyze fatty acid formation are large protein complexes with multiple active sites. The architecture of the mammalian multienzyme (catalytic domains in various colors) is quite different from that of the fungal fatty acid synthase (in gray). Nonetheless, they catalyze the same conserved reaction pathway. See pages 1258 and 1263. Image: S. Jenni and T. Maier

March 10 COVER Saturn’s enigmatic moon Enceladus is a jumbled world of fresh snow plains, old cratered terrains, and long cracks dusted in green organic material. A special section in this issue presents multiple views of Enceladus taken from the Cassini spacecraft during three close flybys. See page 1388. Image: NASA/Jet Propulsion Laboratory/C. C. Porco

April 7 COVER An ant of genus Ectatomma foraging at the Project Amazonas field station in Peru at sunset. An analysis of molecular data and fossils indicates that most subfamilies of extant ants originated 75 to 120 million years ago and diversified by about 60 million years ago. See page 101. Photo: Corrie S. Moreau

April 14 COVER A variety of new and old localization methods are used to visualize components of a cultured human adenocarcinoma (HeLa) cell. The nucleus is labeled with a small-molecule dye (blue), the Golgi apparatus is immunolabeled with quantum dots (yellow), microtubules are genetically tagged with a fluorescent protein (green), and the actin cytoskeleton is labeled with a tetracysteine/biarsenical pair (red). See the special section beginning on page 211. Image: National Center for Microscopy and Imaging Research/B. N. G. Giepmans

May 5 COVER A snapshot from computer simulations of the collision of two neutron stars, about 3 milliseconds after impact. Spiral arms form as the stars shred each other by their strong tidal forces. The colors represent the strength of the magnetic fields produced in the merger, here already amplified in the central regions to values exceeding any previously known in the universe (yellow-white regions). See page 719. Image: D. J. Price and S. Rosswog

May 12 COVER The structure of cowpea chlorotic mottle virus, a plant virus, in its open and closed forms, with a section of the capsid removed from the closed form to illustrate the interior cavity. This virus serves as a biotemplate for viral-based nanomaterials applications. See the Perspective on page 873, which is part of a special section beginning on page 869. Image: J. Hilmer, created with UCSF Chimera

May 19 COVER Artist’s rendering of methane molecules flowing through a sub-2-nanometer carbon nanotube. Mass transport through carbon nanotube membranes is orders of magnitude faster than classical theories had predicted and may be useful for energy-efficient molecular separations. See page 1034. Image: Scott Dougherty

June 9 COVER Merged satellite images from the 1960s and 1990s (30 km east-west by 40 km north-south) of the landscape of northeastern Syria, before intensive agriculture and other recent development altered ancient sites. The red spot near the center marks Tell Brak, the site of a massive ancient city that may have been home to one of the first urban civilizations. A nearby site yielded a stamp seal, dated to about 3500 B.C.E., in the shape of a lioness killing a calf or a gazelle. See page 1458. Main image: Eric Rupley/University of Michigan; inset: Hamoukar Expedition/Oriental Institute/University of Chicago

June 30 COVER Although life is not a game, it does proceed in stages, and there are times when we seem to take one step forward and two steps back. A special section starting on page 1893 includes a News feature on fertility declines and Perspectives about features of various stages of the life cycle, from childhood to old age. Image: Christopher Bickel

August 4 COVER The fungus Neurospora crassa expressing spores in a circadian rhythm, distorted into a circle with four parts representing the four stages of the cell cycle. Unanticipated interregulation links the circadian cycle with cell division through modulation of a cell cycle checkpoint kinase, as described on page 644. Illustration: L. Larrondo

September 1 COVER Three-dimensional Wigner plot (where x is time, y is wavelength, and z is amplitude of the electrical field) of the specific laser pulse found to enhance the photoisomerization quantum yield of retinal in bacteriorhodopsin in the weak excitation limit. The complex periodic pattern induces coherent nuclear motions that are specific to the isomerization reaction. See page 1257. Image: Helena V. Prokhorenko

September 22 COVER A computer-generated rendering of five mathematical surfaces, depicted as glassy objects on a glass tabletop. This image was awarded first place in the illustration category of the National Science Foundation/Science 2006 Visualization Challenge. All of the winning entries are described in a special feature beginning on page 1729. Illustration: R. Palais and L. Benard

October 13 COVER Fluorescent DNA fragments migrating through an acrylamide gel during electrophoresis. The photograph shows 65 capillaries (left to right) each containing a different sequencing reaction. Nearly 4 million such reactions were used to identify mutations in breast and colorectal cancers. See page 268. Image: D. Dressman

November 3 COVER On 3 November 1906, Alois Alzheimer described the pathological characteristics of the neurodegenerative disease that bears his name at the Clinic for Psychiatry at the University of Tübingen, where a centenary meeting is now under way. Images from a state-of-the-art Bielschowsky-stained slide prepared by Alzheimer show the disease’s hallmark pathological lesions–a neurofibrillary tangle at high magnification (left) and a tangle and several neuritic plaques (right). Main image: Corbis; inset: H. Braak and K. Maurer

November 10 COVER The sea urchin, Strongylocentrotus purpuratus, has been a premier model for understanding the gene networks that underlie development. Shown are sea urchin pluteus larvae stained to reveal the ectoderm (green), mesoderm (blue), and endoderm (red). A special section beginning on page 938 describes the sequencing of the genome of the sea urchin and initial insights obtained from the sequence. Images: Esther Miranda and David R. McClay

November 17 COVER Fluorescence optical microscopy image of cadmium selenide nanoparticles. These polyethylene glycol-functionalized nanoparticles have segregated to cracks in a composite film confined between a brittle silicon oxide layer and a silicon substrate. Field of view is 30 by 50 mum. See the special section on materials science beginning on page 1099. Image: S. Gupta and Q. Zhang

November 24 COVER A radar-derived model of Alpha, the larger half of the binary near-Earth asteroid (66391) 1999 KW4. Alpha is an unconsolidated aggregate 1.5 kilometers in diameter; its effective slope ranges from zero (blue) to 70° (red). Its rapid 2.8-hour rotation induces material to flow (arrowheads) from both the northern and southern hemispheres toward the equator. See pages 1276 and 1280. Image: NASA/JPL

December 1 COVER Artist’s representation of communication pathways initiated by cell surface receptors that influence cell physiology and organelle function. This joint special issue between Science and Science‘s STKE highlights new insights into signaling mechanisms that control development and reproduction (see page 1409). Image: Christopher Bickel

December 22 COVER To prove the Poincaré Conjecture, Grigori Perelman used the equations for Ricci flow–a procedure for transforming irregular spaces into uniform ones. In this two-dimensional example, the equations prescribe that negatively curved regions (blue) must expand while positively curved regions (red) contract. Over time, the original dumbbell-shaped surface evolves into a sphere. See the Breakthrough of the Year special section beginning on page 1848. Image: Cameron Slayden/cosmocyte.com, based on data provided by Robert Sinclair