What is the equinox of the indicated position?
• What is the location of the observer? The center of the Earth — geocentric. • What are the strange symbols that appear in the systems of some of the outer planets? These symbols show the locations of satellites for which we know the positions but not the size and rotational information. • What is this “NOMINAL” roll angle? HST must always keep it’s solar arrays pointed toward the Sun — this requires the field of view to have one preferred orientation on the sky for any target and date of observation. The nominal roll will change with time, and can be varied by up to +/- 30 degrees or so if the solar elongation at the time of observation is greater than 90 degrees. See the HST Primer for more details. • How are orientation requirements handled? • If the visit has an ORIENT requirement, the chart is drawn at an angle within the range of the requirement. • If the visit has an ORIENT FROM or a SAME ORIENT requirement, the chart is drawn at an angle which should satisfy the requirement
