For people on the Earth, the Sun rises in the east and sets in the west. As seen from the Earth it is the Sun that revolves around the Earth. Path of the Sun as seen from the Earth is called ecliptic. Solar & lunar eclipses are related to ecliptic plane. Since Rahu & Ketu cause eclipses mythologically, ecliptic is important to understand the astronomy of Rahu & Ketu.
Garnet is found in different colour shades and quality. Typically, brownish shade is used for Rahu, whereas deep red shade is used for Sun. It has many more shades and as the research progresses it may be possible to use other colour shades of this stone to boost many more grahas.