Sundials must face True North, and the style (either a sharp straight edge or a thin rod, generally found at the gnomon's edge or tip) must be aligned with the Earth's rotating axis. You may also place your sundial such that no shadow is cast at high noon. In this case, you would need a second clock to know when it was time to reset the sun.
It is important to remember that the purpose of a sundial is to indicate the time, so it does not matter which direction the dial points. However, since the sun's position in the sky changes throughout the year, knowing where true north is allows you to set your dial at the right time of year.
In conclusion, a sundial does not need to point north, but it does need to face true north in order to work properly.
Sundials used for telling time instead point south.
The sun moves across the sky each day, causing the shadow on the dial to shift if it is being used for telling time. If you are using the dial to mark the hours, it is important that it is kept in alignment with solar noon so that its indication of time is correct.
A sundial can be used for marking seasons as well as hours. In countries where daylight savings time is used, there is no need to reset the clock at spring or fall equinoxes. The dial will indicate the right time automatically every day at midnight when the clocks are moved forward or back.
During World War II, American soldiers used sundials made from empty beer bottles to tell time in Europe. After the war, they were able to return home and buy real American-made sundials for their lawns. Today, beer bottle sundials are popular gifts for both men and women.
Sunlight strikes the upper part of the dial near sunrise and sunset, causing the shadow to move slowly west to east across the dial.
A horizontal sundial should be positioned on a fully level surface or on a sundial pedestal with the gnomon pointing celestial north to read time as precisely as possible (90 degN).
Fully exposed areas on your property may not be visible, but they can still function as good places to locate a sundial. For example, if you have a large yard but no driveway, you could put your clock in a prominent location within the yard and mark it so that you will never forget what time it is. Or maybe you build a shed for yourself anywhere from the house, but only use it once in a while. These are good options for exposing new parts of your property to help visitors and neighbors find their way around easily.
The best option is a site that gets direct sunlight most of the day. If you live in an area that has cold winters, consider placing the dial face down to protect it from freezing. Of course, you should pick a location that is safe from traffic accidents and vandalism. Make sure that children cannot reach it either. The dial should be at least 1 meter (3 feet) high for best reading accuracy.
There are many different types of sites that would work well for a sundial.
To read a sundial, first position it on a level surface in a sunny location. Rotate the sundial so that the gnomon, or the pin on the sundial that casts a shadow, points north in the northern hemisphere and south in the southern hemisphere. Then look at where the gnomon's shadow falls on the sundial. A line connecting the sun's rise point with its set point will pass through the center of the dial. The angle between this line and 12 o'clock is equal to the latitude of the site. For example, if the line passes through 7:00, then the latitude is 0 degrees; if it passes through 15:00, then the latitude is 90 degrees.
Sundials were used by ancient astronomers to measure the time it took for the sun to reach a certain point in the sky. They were also used as clocks during daylight hours. Sundials are very simple devices that use mirrors or lenses to bend light toward a gnomon (an upright post) that reaches into the ground. The position of the gnomon in relation to the sun indicates the time. Because the earth is not a perfect sphere but an oblate spheroid, latitude affects when the sun appears at different times throughout the day. Sundials are most accurate when they are located away from the equator and when the site is relatively dry. Moisture causes the gnomon to move, thus causing time errors if it is not read again soon after installation.
People have been using sundials since ancient times.
The marks on a sundial's flat surface symbolize each hour of daylight. The gnomon, or vertical rod, in the middle of the dial throws a shadow on this flat surface as the sun travels across the sky from east to west. This is why a gnomon is called a "shadow caster."
The position of the gnomon determines what time it is. If the gnomon is standing up straight, then it's morning. If it's lying down, then it's night. The closer the gnomon is to midnight, the shorter its shadow will be.
Sundials have been used for thousands of years because they are very easy to read. You only need to look at the shadow cast by the gnomon to know what time it is. Although modern technology has improved on the sundial design, it still uses gravity and metal rods to tell time.
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When the earth spins on its axis, the sun appears to "move" across the sky, casting shadows on things. In a standard horizontal sundial, the base platform remains stable while the gnomon moves to reflect variations in the earth's axial tilt. Because the angle of the earth's axis of rotation changes over time, so does the direction that the shadow falls on different parts of the globe.
In a vertical sundial, which uses an upright instead of a horizontal platform, the gnomon is always tilted toward the north or south pole. This allows us to watch the movement of the polar night and day for free. During a total solar eclipse, when the path of totality crosses the United States, many people see a dark silhouette of the standing gnomon against the bright surface of the remaining sunlight.
In a dial-shaped sundial with both upper and lower panels, the shape of the panel facing up determines whether the gnomon is tilted toward the north or south pole. If it is tilted toward the south, there will be more evening than morning sunshine during summer months. During winter, however, this same panel is facing down, so there is less darkness during the day and more daylight at dawn and dusk.
Dial-shaped sundials were most common in Europe and the Americas. They're still made today, but they are mostly used for decorative purposes rather than for telling time accurately.