Mirrors at Melbourne’s Shrine of Remembrance
Correct for Daylight Saving Time
The armistice that ended the First World War was signed at 5am on 11 November, 1918. The formal agreement however, did not take effect until six hours later. Thus the fighting officially stopped along the Western Front at 11am.
When the Shrine of Remembrance in Melbourne was completed in 1934 it included a special visual effect to recall that moment in history. At the eleventh hour of the eleventh day of the eleventh month a ray of sunlight would illuminate the word Love in the inscription Greater Love Hath No Man on the Stone of Remembrance. The design was such that for the next five thousand years this event would occur within 2 minutes of 11am on 11 November. Frank J. Doolan's 1934 paper The Survey of the Shrine of Remembrance in Melbourne, provides an overview of that monument's design and construction.
Figure A : Diagram of the Shine showing the location of the two mirrors.
Melbourne's adoption of daylight saving time in 1971/72 however, caused a problem as the ray would now illuminate the stone at midday. An artificial light from a theatre spotlight was relied upon until 1976, while a solution was sought.
A method of redirecting the sunlight’s path was devised by former Natmap surveyor and then RMIT Lecturer Frank Johnston. Frank recalls that it was Frank Doolan, mentioned above, who requested RMIT’s assistance. One fixed and one adjustable mirror as shown in Figure A above would redirect the sunlight and correct for the one hour time difference. The incoming sunlight would first strike a precisely inclined, adjustable mirror installed on a pillar in a steel tube on the outer walkway. (When not in use the tube can be capped to protect the mirror from Shrine visitors). The adjustable mirror would thus reflect the sunlight up to a hole in the roof, where a horizontal mirror would direct the ray through a hole in the ceiling and down to the granite stone of remembrance some 35 metres below. (The second mirror is about half the size of an A4 page, and installed only on Remembrance Day morning). Slight movement in the Shrine structure requires that the alignment of the mirrors be checked each year prior to the ceremony.
Bridie Smith’s 2014 article in The Age Victoria, titled Bending the Light for Remembrance Day (http://www.theage.com.au/victoria/bending-the-light-for-remembrance-day-20141106-11hbkt.html) included a video of Frank undertaking the installation and adjustment of the mirrors. The video may be viewed via this link courtesy ABC and Fairfax Media.
In 2015 Frank gave a presentation to The Institution of Surveyors, Victoria, Regional Conference at Wangaratta, Titled Bending the Beam, the PowerPoint presentation may be accessed at http://www.surveying.org.au/techinfo.php but is available here as a PDF with improved graphics. The presentation shows photographs of the mirrors’ installation and the spherical trigonometrical calculations required to precisely align the adjustable mirror. More detail can be read below.
Compiled by Paul Wise, 2017
Past and future settings for the adjustable mirror
The US National Oceanic and Atmospheric Administration’s Excel version of their free Solar Position Calculator (https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html) generates solar coordinates for any date and time in the modern era. Modifying the solar calculator to provide solar coordinates at 10am and 11am for 11 November for any range of years and adding Frank’s equations allowed the required Azimuth (direction) and Zenith Distance (vertical angle) of the mirror’s normal to be calculated. The table below shows the settings for 11 November from the year 2000 to 2050.
At the bottom of the table is the calculation using Frank’s original 25 year mean of solar position which differs from the spreadsheet calculation by 3” of arc in Azimuth and 1” of arc in Zenith Distance. These differences come from the 25 year mean of the solar coordinates being only quoted to an accuracy of around 5” of arc and the various ways different calculators evaluate trigonometrical expressions.
The table below does not show all steps and only 2 decimal places are visible to save space.