Continuous Viewing Zones (CVZ) Requirements
- Observations performed in either of the 2 (northern and southern) HST Continuous Viewing Zones (CVZ) can be very desirable and appear very worthwhile to the TAC because of their much greater observational efficiency.
- These periods can vary in size and duration given the exact location of the target, and due to updated HST orbital ephemerides, some marginal CVZ periods may even disappear, though they may still be near-CVZ opportunities of greater than normal orbital duration.
- CVZ observations are very limited resources, and should be investigated carefully before proposing for them.
- A more rigorous Phase II-style test proposal may help to test unusual or demanding situations, but that is still susceptible to later changes in the orbital ephemeris for HST, so one should be mindful of that possibility even though following the Phase I rules and advice in the standard Phase I documents (Call for Proposals, the Phase I Roadmap, and/or the HST Primer).
- Depending on the filters involved (redder filters are typically more susceptible), the risk of scattered light and higher background is also greater for CVZ observations.
- The CVZ requirement must be proposed for and specified in Phase I proposals in order for it to be used in Phase II.