Contents

- 1 How do you make a simple sundial?
- 2 How do you set up a garden sundial?
- 3 Who invented sundial?
- 4 Are sundials accurate?
- 5 What is the angle of a gnomon?
- 6 How do you calculate a sundial?
- 7 How tall is my shadow?
- 8 Does a sundial work on the equator?
- 9 Can you put a sundial on a wall?
- 10 Who invented time?
- 11 How old is the oldest sundial?
- 12 Why are sundials not used today?

## How do you make a simple sundial?

Take your plate and plastic straw outside. Put the plate on the ground and poke the straw through the hole you made. Slant the straw slightly toward the line you drew. Carefully rotate the plate so the shadow of the straw lines up with the line you drew.

## How do you set up a garden sundial?

Sundials need to point in the direction of True North, and the style (either a sharp straight edge or thin rod, often located at the edge or tip of the gnomon) must be aligned with the Earth’s rotational axis.

## Who invented sundial?

The mathematician and astronomer Theodosius of Bithynia ( c. 160 BC to c. 100 BC) is said to have invented a universal sundial that could be used anywhere on Earth.

## Are sundials accurate?

A sundial is designed to read time by the sun. This places a broad limit of two minutes on accurate time because the shadow of the gnomon cast by the sun is not sharp. Looking from earth the sun is ½° across making shadows fuzzy at the edge. The actual construction of a sundial can be very accurate.

## What is the angle of a gnomon?

The gnomon of the vertical sundial makes an angle of 90° –L with the vertical (that is, an angle L with the horizontal), as shown in the side view in Figure 5. In the southern hemisphere, the vertical dial is north-facing. Unlike the equatorial dial, the hour angles are not equally spaced.

## How do you calculate a sundial?

The formula for calculating the hour lines (theta) on a horizontal sundial is:

- tan(theta) = tan(HA) x sin(lat)
- theta = the resulting dial hour angle measured from the noon line (- is left of the noon line, + is right of the noon line)
- HA = the hour angle of the sun from the noon meridian, expressed in (+/-) degrees.

## How tall is my shadow?

The length of shadow to your height is proportional to 1/Tangent (sun’s altitude). If the sun is low in the sky (10 degrees), your shadow would be 5.67 times as long as your height. The corresponding ratio at 5 degrees is 11.43. (So an average height person (5.8 feet) would have a 66 foot long shadow).

## Does a sundial work on the equator?

The dial plate of an equatorial sundial lies precisely in the plane of the equator, which means that the summer shadow falls on only the uppermost face of the equatorial plate sundial while the winter shadow falls on only the underneath face.

## Can you put a sundial on a wall?

On the front of a house A wall facing the south (north) will be adequate for a vertical direct south (north) dial. A wall facing east (exactly or declining between 80° and 100°) or facing west, is an excellent place for a nice direct east, a direct west or a vertical declining sundial.

## Who invented time?

The measurement of time began with the invention of sundials in ancient Egypt some time prior to 1500 B.C. However, the time the Egyptians measured was not the same as the time today’s clocks measure. For the Egyptians, and indeed for a further three millennia, the basic unit of time was the period of daylight.

## How old is the oldest sundial?

The first sundial was created more than 5,500 years ago in the year 3500 BCE. Sundials have even been found in Ancient Egyptian ruins! Many ancient cultures including the Egyptians, Greeks and Romans used sundials. The Romans were the first to divide the day into 12 hours to better mark the time and meetings.

## Why are sundials not used today?

The most common reason for a sundial to differ greatly from clock time is that the sundial has not been oriented correctly or its hour lines have not been drawn correctly. For example, most commercial sundials are designed as horizontal sundials as described above.