What's where on Mauna Kea

The 7.5 minute USGS topographic quadrangle for Mauna Kea is available online. Unfortunately, many of the observatories have been built subsequent to the most recent update some 20 years ago.

The observatories on Mauna Kea do not share the geodetic favor that was so helpful on Mt. Hamilton. The environment on Mauna Kea is not conducive to casual geodetic occupation, and the few surrounding peaks of equal size are similarly difficult. Nevertheless, the NGS provides a wonderful resource that permits the inspection of the data sheets for all the reference marks in the US, including those on the Mauna Kea summit.

Putting these bits of information together creates this map. Each of the control points from the NGS data sheets is marked. The approximate location of most of the telescopes are also marked. The VLBA antenna is conspicuously absent, but it is located off the image approx. 2km south-southeast of the summit at the 12200 foot level.

From scaling this map I estimate that the position of Keck I is
W 155:28:28.8
N 19:49:35.0
using the 1983 North American Datum.
Because Keck is not marked on the quadrangle, these positions could be wrong by as much as an arcsecond. A much better set of positions for most everything is at the IFA web site.

Several aspects of these data need to be emphasized.

• Note that the only NGS reference marks are on the N-S ridge with the original UH telescopes. There are no marks along the E-W ridge leading to Keck and Subaru.
• The long/lat grid marks on the USGS topo are for the 1927 North American Datum. The 1927 NAD is based on the 1866 Clarke ellipsoid and tied to the earth at Meade Ranch, Kansas; it is a very bad fit to the geoid in the vicinity of Hawaii. The marks for the 1983 North American Datum would be 291 meters west and 341 meters north of the marks shown.
• The 1983 NAD uses a different ellipsoid than the system in use by the GPS satellites, and there is active discussion going on about replacing the 1983 NAD with yet a better datum.
• The USGS topo has been rotated to align with north on the Universal Transverse Mercator (UTM) grid (the difference between geodetic north and UTM grid north is given on the data sheets).
• The USGS topo shows only those domes which were present in 1982. The dome shown at the current location of the Gemini is actually a previous UH telescope, now destroyed.
• The construction of the CFHT may have obliterated the control point with NGS PID TU2308.
• It is not clear that there have ever been any gravity measurements on Mauna Kea, nor any transit observations of the sort that would determine the deflection of the vertical. This means that there is no way to get an accurate value for the astronomical long/lat of Keck.
• There must be other survey data not in the NGS database, for the VLBA antenna would not be able to obtain fringes if its position were not known within a few meters.