BRICKS. As you near the end of the Granite Tors Walking Track, a strange object will emerge from the bush - an imposing cylindrical brick building with a 9m diameter dome. This is the former Orroral Geodetic Observatory that was is operation between 1974 and 1998, until the Mt Stromlo sight took over. In 2016, the building was added to the ACT Heritage Register and has recently been tidied up. You can now go inside.
According to the Heritage Notice, the Observatory was “Australia’s fundamental geodetic facility, boasting caesium atomic clocks providing Australia with its official time, and a range of sensitive instrumentation catering to Satellite Laser Ranging and Global Positioning Systems, enabling measurement of the Earth’s geoid with millimetre accuracy.”
BLOCKS. There are three 1-metre high, cylindrical blocks surrounding the observatory. These are known as survey pillars, with one looking out over the Orroral Valley. According to the Heritage Notice, “the ACT Surveyor‐General takes satellite readings of survey pillar NM/C/106 multiple times per decade. Because the pillar was positioned with the millimetre‐accuracy of SLR technology, its precise location on the Earth’s surface has been recorded.” It is used to update the Geodetic Datum of Australia 1994 (GDA94). There is also a very small Centre Survey Marker that is used as part of the measurement system.
ROCKS. With a walking track called “Granite Tors”, you will expect to see plenty of rocks and boulders, of all shapes and sizes. In fact, the granite rock is essential to maintain the ‘bricks’ and ‘blocks’ firmly in place. You will also find GZ near one of these impressive tors.
YOUR MISSION.
Collect information within a 25m radius around the Observatory .
The Bricks. At the Posted Coordinates, look for the plaque on the Observatory door. R = sum of letters for the name of the USA-Australia ?????? Treaty (6 letters). Use A=1, B=2, etc. S = sum of letters for the name of the ????? transmitter (5 letters).
Block 1. Take a few steps back from the door. Look to your LEFT. 10-12m away, you will see Block1. T = number of 12mm diameter circles around edge of large metal disc.
Block 2. Return to the door. Now walk around the Observatory to your right. You will see a rocky path leading up to the viewing platform. Head up there. Enjoy the spectacular view. There is a plaque on Block 2. U = number of letters in the first word (a person's first name). V = number of 12mm diameter circles around edge of large metal disc.
Block 3. At Block 2, turn around, facing back into the bush. Cast your eyes over the end of the right fence railing, looking into the bush. About 25m away, you will see Block 3. It is also about 15m to the left of the Observatory. Walk directly to it, down the large flat boulder. W = number of 12mm diameter circles around edge of large metal disc.
Centre Survey Marker. Return to the door. Now, walk back to the right side of the Observatory and stand facing into the bush with you back against the Observatory wall. (You should be near the path leading up to Block 2 and be standing on top of a circular metal plate.) Walk 6-7m straight, over the medium-sized boulder. Look very carefully on the ground for a small, silver, cylindrical block about 3cm high, fixed into the rock. *Don’t stub your toes*. Near it is a metal inscription of the survey marker. It is firmly cemented in the ground. XYZ = three digits in the inscription “NMV/C/###”.
GZ. The Observatory might be an impressive man-made object, but GZ is a reminder that nature can produce its own 'impressive monument’. The cache is at S35 38.(V-T-W)(T-W)(U) E148 56.(Z)(X+Y)(R-S). Follow the path, then turn into the bush.
Checksum: S = 25, E = 37