Coordinates for Observatories on Cerro Tololo and Cerro Pachon

Here is a table of the current best estimates of the geodetic latitude and longitude (WGS-84; south and west are negative), geodetic height (h, measured with respect to WGS-84 ellipsoid), geoid undulation (N; from EGM96 model), elevation (H) with respect to EGM96 geoid ("mean sea level"), and geocentric latitude.

We have used the short name for the telescopes Wisconsin H-Alpha Mapper (WHAM), Las Cumbres Observatory 1-meter Telescope #4, #5,and #9 (LCOGT Stellan-A,B,C), Andes LIDAR Observatory (ALO). All PROMPT are 0.41-m, Evryscope-South Telescope was formerly known as PROMPT-4.

Typical uncertainties in latitude and longitude are 0".10, and typical total uncertainties in geodetic heights and elevation are probably better than +-1 m for observatories on the Tololo Plateau and SOAR (tied together through a combination of precise geodetic positions for survey monuments and differential elevations from survey maps), and roughly +-5 m for other observatories (whose elevations were determined through a blend of GPS and Google Earth; there is room for improvement on these!). The elevations correspond to ground level at the observatories, and so far do not take into account the height of the telescope. These data come from a 2012 study by Eric Mamajek (CTIO) combining data from historical survey maps with new measurements using GPS and Google Earth.

Note that astronomical latitude and longitude has only been reported for the Schmidt telescope on Cerro Tololo (Harrington, Mintz Blanco, Blanco, 1972; Contributions to CTIO No. 126). They report that the astronomical and geodetic coordinates differed at the ~30" level, due to deflection of the vertical (due to the local gravitational field on Tololo). For a rough estimate of the astronomical latitude, add 12".7 to the geodetic latitude. For a rough estimate of the astronomical longitude (for e.g. meridian transit times), subtract 31".6 to the geodetic longitude. Harrington et al. (1972) estimated the astronomical latitude, longitude for the Schmidt telescope to be (-30 09 55.5, -70 48 52.7).

The latitude and longitude for CTIO in the 2013 edition of the Astronomical Almanac and in recent versions of the iraf file obsdb.dat appear to correspond to the astronomical latitude and longitude (tied to the Harrington et al. 1972 study), not a geodetic position that one would measure with GPS or on Google Earth. So the value listed in the Astronomical Almanac and in the iraf obsdb.dat file are useful for estimating meridian transit times and airmasses. However the geodetic or geocentric positions may be more appropriate for other calculations (e.g. those where geocentric parallax may be important, occultation predictions, etc.).