Due to overlaps in imaging stripes, the SDSS sometimes observes the same object more than once. In such cases, we select one observation as PRIMARY (mode=1). Each astronomical object is assigned a thingID, and each time that "thing" is observed (detected in SDSS imaging), it assigned a separate objID.
Information about each astronomical "thing" is stored in the thingIndex table; thingIndex is a thin coupling table designed only to connect repeat observations. Information about each individual observation (detection) is in the photoObjAll table. (Note that photoObj contains only the primary [mode=1] and secondary [mode=2] observations of each "thing.") The detectionIndex table connects each objID to the thingID it corresponds with.
|IAU name||objid||thingid||mode description|