Sky in KML
KML 2.2 supports presentation of astronomical as well as terrestrial data (as shown in Figure 1-6). When you include a special hint (hint="target=sky") at the start of a KML file, the browser interprets the data in a different way and projects it onto a virtual celestial sphere that surrounds the Earth. In Sky mode, the Google Earth camera looks up at the heavens rather than down at the Earth. The main difference from the KML creator’s point of view is that you need to perform some arithmetic to convert astronomical coordinates (right ascension and declination) into terrestrial coordinates (longitude and latitude). Everything else in KML works the same in both Sky and Earth modes.
Figure 1-6 Travel through space. This KML file contains a placemark and balloon for a famous planetary nebula. To display sky data in an Earth browser, include the special KML hint, and convert astronomical coordinates to Earth coordinates (see Appendix B).
If you’re primarily interested in using KML to show Sky data, read Appendix B, “Sky Data in KML,” first.