Added Filippenko model, updated B&S refractivity

README.md

@@ -63,6 +63,8 @@ The package contains the following files:
 - `misc.py` 				: Contains several miscellaneous functions, e.g. to quickly calculate the refractive index.
 - `refractionModels.py`		 		: Contains various atmospheric models that can be used to calculate the atmospheric refraction
 - `refractivityModels.py` 		: Contains various functions from literature to calculate the refractive index. Some examples of works included are Ciddor (1996), Barrell & Sears (1939), SLALIB, Owens (1967) and Edlen (1966).
+- `observatories` 				: Contains a dictionary with the average atmospheric conditions for various large observatories around the world.
+
 
 
 ## The Ciddor refractivity model
@@ -186,7 +188,7 @@ Included are
 | ---------- | -------- | ------- |
 | Barrell & Sears (1939) | `BarrellAndSears()` | Outdated model, especially poor for short wavelengths. |
 | Ciddor (1996) | `Ciddor()` | Only at standard atmosphere. CO2 density can be changed. |
-| Edlen (1953) | `Edlen1953()` | Only at standard atmosphere. Function requires wavelength only. |
+| Edlen (1953) | `Edlen1953()` | The equation by Edlèn, 1953, combined with modification from Barrel (1951), to include temperature, pressure and humidity dependence. |
 | Edlen (1966) | `Edlen1966()` | Only at standard atmosphere. Function requires wavelength only. |
 | Owens (1967) | `Owens()` | - |
 | Bonsch & Potulski (1998) | `BonschPotulski()` | Function does not include humidity |
@@ -199,9 +201,8 @@ The last function extracts the refractive index from the `pyslalib.sla_refro()`
 
 ## Quick functions
 
-Some functions that assume default conditions for the atmosphere. Then only the wavelength and zenith angle are required to calculate the refraction and dispersion. 
+Some functions can make use of the `observatories` dictionary as input. These include default average conditions of the atmosphere at these locations. When these are used, only the wavelength and zenith angle are required to calculate the refraction and dispersion. 
 
-Presently, only the `'STANDARD'` and `'CERRO_ARMAZONES'` flags are known. Contact the author to add additional standard conditions.
 
 ```python
  # Quick refractive index
@@ -214,6 +215,18 @@ rq = quick_refraction(l1, zenith_obs, conditions='STANDARD')
 dq = quick_dispersion(l1, l2, zenith_obs, conditions='STANDARD')
 ```
 
+Presently, several observatories are known. These can all be found in the `observatories` dictionary. Contact the author to add additional standard conditions.
+| Observatory | Flag | Notes | 
+| ----------- | ---- | ----- |
+| standard conditions | `STANDARD` |  |
+| Cerro Armazones | `CERRO_ARMAZONES` | Location of the future ELT |
+| Cerro Paranal | `CERRO_PARANAL` | Location of the VLT, VISTA, VST, NGTS and SSO |
+| Roque de los Muchachos Observatory (La Palma) | `LA_PALMA` | GTC, INT, WHT, NOT, and others. |
+| La Silla Observatory | `LA_SILLA` | ESO 3.6m telescope, NTG, BlackGEM and others. | 
+| Las Campanas Observatory | `LAS_CAMPANAS` | Site of the future GMT |
+
 ## Other
 
-This package also contains a python native port of the `SLA_REFRO()` routine of the pyslalib package, which was originally written in FORTRAN by P.T. Wallace. It can be called directly using `sla_refro()`. When using the same units as the other refraction functions, you might prefer using `slalib_refraction()` or `slalib_dispersion()`.
+This package also contains a python native port of the `SLA_REFRO()` routine of the pyslalib package, which was originally written in FORTRAN by P.T. Wallace. It can be called directly using `sla_refro()`. When using the same units as the other refraction functions, you might prefer using `slalib_refraction()` or `slalib_dispersion()`.
+
+Finally, the dispersion model used by Alexei Filippenko in 1982 is also included. This model is a combination of the (modified) Edlèn equation and a plane-parallel atmospheric geometry. This calculation can be accessed by calling the `Filippenko1982()` function.