Free Astronomy Magazine March-April 2018

19 MARCH-APRIL 2018 SPACE CHRONICLES The three-dimensional video pro- vides a look at the fantastic topog- raphy of the nebula. A torrent of ultraviolet radiation and stellar winds from the massive, central stars of the Trapezium star cluster have carved out a cavernous bowl- like cavity in the wall of a giant cloud of cold molecular hydrogen laced with dust. Astronomers and visualizers worked together to make a three-dimensional model of the depths of this cavernous re- gion, like plotting mountains and valleys on the ocean floor. Colorful Hubble and Spitzer images were then overlaid on the terrain. The scientific visualization video takes the viewer on a breathtaking flight through the nebula, follow- ing the contours of the gas and dust. By toggling between the Hub- ble and Spitzer’s views, the movie shows strikingly different details of the Orion Nebula. Hubble sees objects that glow in visible light, which are typically in the thousands of degrees. Spitzer is sensitive to cooler objects with temperatures of just hundreds of degrees. Spitzer’s infrared vision pierces through obscuring dust to see stars embedded deep into the nebula, as well as fainter and less massive stars, which are brighter in the infrared than in visible light. The new visualization helps people experience how the two telescopes provide a more complex and com- plete picture of the nebula. The visualization is one of a new generation of products and experi- ences being developed by the NASA’s Universe of Learning pro- gram. The effort combines a direct connection to the science and sci- entists of NASA’s Astrophysics mis- sions with attention to audience needs to enable youth, families, and lifelong learners to explore fundamental questions in science, experience how science is done, and discover the universe for them- selves. The three-dimensional interpreta- tion is guided by scientific knowl- edge and scientific intuition. Starting with the two-dimensional Hubble and Spitzer images, Sum- mers and Hurt worked with experts to analyze the structure inside the nebula. They first created a visible- light surface, and then an underly- ing structure of the infrared fea- tures. To give the nebula its ethereal feel, Summers wrote a special rendering code for efficiently combining the tens of millions of semi-transparent elements of the gas. The custom- ized code allows Summers to run this and other visualizations on desktop workstations, rather than on a supercomputing cluster. The other components of the neb- ula were isolated into image layers and modeled separately. These ele- ments included stars, protoplane- tary disks, bow shocks, and the thin gas in front of the nebula called “the veil.” After rendering, these layers and the gaseous nebula are brought back together to create the visualization. The three-dimensional structures serve as scientifically reasonable approximations for imagining the nebula. “The main thing is to give the viewer an experiential under- standing, so that they have a way to interpret the images from tele- scopes,” explained Summers. “It’s a really wonderful thing when they can build a mental model in their head to transform the two-dimen- sional image into a three-dimen- sional scene.” This movie demonstrates the power of multi-wavelength astronomy. It helps audiences understand how science is done — how and why as- tronomers use multiple regions of the electromagnetic spectrum to explore and learn about our uni- verse. It is also whetting astrono- mers’ appetites for what they will see with NASA’s James Webb Space Telescope, which will show much finer details of the deeper, infrared features. T his visu- alization is an excerpt from a longer sequence that explores the Orion Nebula using both visible and infrared light. Two correlated computer models were created based on vis- ible-light observations from the Hubble Space Telescope and infrared-light obser- vations from the Spitzer Space Telescope. [NASA, ESA, F. Summers, G. Bacon, Z. Levay, J. DePasquale, L. Hustak, L. Frattare, M. Robberto and M. Gennaro (STScI), and R. Hurt (Caltech/IPAC) - Acknowledgement: R. Gendler] !