Add lunar keywords

[wlandry]

A number of our observatories, include space missions like WISE, record characteristics about the moon. IRTF has the most complete information

• LUN_FLI: Fraction Lunar Illumination (FLI) is the percent of the Moon's visible disk illuminated by the sun. Range is 0.0 to 100.0.

• LUN_LIGHT = The lunar light level based on the lunar elevation (EL), and Fraction Lunar Illumination (FLI) values from JPH Horizon. Values are:

  • dark = 0% <= FLI <25.0%, or Moon Elevation < 0 degrees.
  • gray = 25% <= FLI < 75.0% with Moon Elevation > 0 degrees.
  • bright = 75.0 <= FLI, and Moon Elevation > 0 degrees.

• LUN_SEP = The lunar separation in degrees of RA,DEC – moon.

• LUN_EL = The lunar position's Elevation in degrees, +90.0 to -90.0

• LUN_AZ = The lunar position's Azimuth in degrees. 0-360. 0=North, 90=east.

This seems common enough, especially for ground based observatories, such that at least some of these keywords should be supported.

[pdowler]

This looks like metadata that would go into Environment (Observation.environment) as it describes the conditions during the observation.

We still need to consult more widely to figure out which things and representations are "common" and which are needed to satisfy use cases. Use cases in this area are almost exclusively "data discovery" in nature so that would mean picking options that most effectively enhance that general use case.

[pdowler]

Defer to later