Astronomical Computing

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Sundial of Trinita dei Monti in Rome

Written by Toshimi Taki
March 2, 2008

Spanish Steps and Trinita dei Monti

My wife and I went to Rome in August 2007 for sightseeing. When we visited Piazza di Spagna (The Spanish Steps), the famous spot from an Audrey Hepburn's movie, "Roman Holiday", I noticed a sundial on the front wall of a nearby church, Trinita dei Monti. Trinia dei Monti actually stands above the Spanish Steps.

The Sundial

The sundial is vertical type and the wall is facing to South-West-West. We visited the place in the morning and the Sun was behind the charch as seen in the photographs above. The sundial has hourlines and the other lines. I did not know what the horizontal lines were and I made some calculations after I returned from Rome.

Result of Calculation

- Data for Calculation
Latitude of Rome: 41.9 degree.
Direction of Wall: 75 degree westward from South (See Figure 2)

- Result of Calculation --> Figures 3 to 5.
The horizontal lines show hours from the sunset.

Figure 1. Sundial of Trinita dei Monti

Figure 2. Direction of Wall

Figure 3. Hourlines

Figure 4. Lines for Time from Sunset

Figure 5. Comparison

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