Two Virtual Reality Modeling Language (VRML) models - one representing the Milky Way Galaxy and another the Interplanetary Dust Cloud - are described on this page. These models can be used as instructional tools. They can be manipulated (rotated, panned and zoomed) using a VRML browser, giving the user the sense that the models are real, tangible objects. The models described here are VRML 1.0 models which, unfortunately, do not display properly in all VRML 2.0 browsers.
The Milky Way VRML2 model is based on a statistical representation of the three-dimensional density distributions of stars of various spectral types (colors). Hot, luminous blue stars are concentrated close to the Galactic plane and in the spiral arms. Cool, red stars are distributed in a thicker layer about the plane and concentrated in the bar ("bulge") at the Galactic center. The stellar density distributions are those published by Wainscoat et al. (1992) for the main disk, and Dwek et al. (1995) for the bulge. A Monte Carlo method was used to sample the density distributions, yielding a 44,000-star representation of the Galaxy. The real Milky Way contains about 100 billion stars. Using a VRML browser, one can "fly into" the model to the location of the solar system to view the Galaxy from our unique vantage point in the disk, about 8.5 kpc from the Galactic center. Our understanding of the shape and orientation of the Galactic bulge was improved with the help of the COBE DIRBE near-infrared data. At visible wavelengths, those to which our eyes are sensitive, interstellar dust clouds block background starlight, producing an obstructed view of the center of the Galaxy, as is illustrated in the Multiwavelength Milky Way. The VRML model is similar in many respects to the Faint Source Model used by the DIRBE Team to represent the Galactic near-infrared starlight in the search for the cosmic infrared background (Arendt et al. 1998).
The Milky Way VRML model is one of six such models created for an educational project called iUniverse, which is currently under development.
The Interplanetary Dust Cloud VRML2 model represents the distribution of dust in the solar system, as derived from the COBE DIRBE observations. Like the Milky Way model described above, the dust distribution is represented statistically, using a Monte Carlo technique. Careful modeling of the DIRBE infrared data led to the understanding that dust in our planetary system is concentrated in several distinct structures: a smooth cloud, three asteroidal dust bands, a circumsolar ring near 1 AU, and a small cloud of dust that trails the Earth in its orbit around the Sun (Kelsall et al. 1998). The points representing each cloud component in the VRML model were assigned a unique color, enabling the components to be distinguished from each other.