# COBE "Science on a Sphere" Images

This page provides access to a number of images that have been formatted to be compatible with "Science On A Sphere", a 3D visualization system developed by the National Oceanic and Atmospheric Administration (NOAA) and implemented at NASA's Goddard Space Flight Center (GSFC) (among other places). These images are provided as a courtesy to our users; they do not constitute an endorsement of any product or service.

These are projections of the images available here. The data can be downloaded from here.

 This COBE/DMR data has been reprojected from the Mollweide image available at the above link. Image Credit: NASA / COBE Science Team

## Projection Conventions

The Science on a Sphere (SOS) exhibit was originally designed to show the Earth and various other planets, which are easily represented as spheres we view from the outside. When using the Science on a Sphere to represent the sky, one has to pick some nontrivial visualization conventions. This is because it is much more natural to think of the sky as a sphere that we view from the inside.

One possible approach is to map the sky onto the sphere as directly as possible. When we look in some direction on the sky, we can specify that direction as a vector, and color the sphere at the tip of that vector according to what we see. This means that the sky would look correct when viewed from the center of the sphere. However, when viewed from outside the sphere, all of the features on the sky (constellations, for example) would appear to be backwards---mirror images of how we usually see them.

To rectify this problem, one can do a parity transform of the projection. This can be thought of as mapping each point on the sphere to the point directly opposite (and then doing some rotations so the North Pole is on top again, if desired). This will turn the constellations right side out, for a viewer outside the sphere, although it becomes slightly more difficult to explain how the image on the sphere corresponds to the visible sky.

The Science on a Sphere images here use this convention, where the constellations are right-side-out when seen from the outside. Note that if the other convention is desired, this can be achieved by flipping the images left-to-right in an image editing program.

The Science on a Sphere projection is a simple latitude-longitude grid, also known as an Equatorial Cylindrical Equidistant projection (ECE). See the SOS web site for details and sample images: http://sos.noaa.gov/index.html

The images projected here have the galactic center in the center of the image. The Galactic North pole corresponds to the entire top edge of the image, and the Galactic South pole corresponds to the entire bottom edge of the image. The left and right edges have galactic longitude l=180 degrees. This orientation was chosen because the galactic center is usually the most recognizable, and so it was put in the center of the rectangular image.

Also available:

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