Q&A for How to Read a Sundial

No—a sundial works by casting shadows that indicate the time based on the position of the sun. A sundial won’t work if the sun isn’t visible, so you can only use it during the day when it’s clear enough out for the sun to cast a shadow. However, there is a similar device called a moondial that you can use at night, tracking shadows based on the moon’s position.

It depends on how carefully the sundial is designed and oriented. Most of them aren’t truly accurate to within more than about 10 minutes.

A shadow clock is any kind of timepiece that tracks the passage of time using the movement of shadows, usually cast by sunlight. A sundial is the most common type of shadow clock. There are also moondials, which track shadows cast by the moon at night.

There are various definitions. You can take the farthest points N, E, S and W inside your time zone, then take the central point that is equidistant to those 4 points. You could also draw a line from north to south that is equidistant from the vertical edges of your timezone. However, I'm curious why anyone would need this? The time is the same in the entire timezone.

During those gap periods, New York is only 4 hours behind London, as opposed to the 5 hour difference, when both cities are on daylight saving or when both cities are off. Because there isn't a moment at which London is on and New York is off daylight saving, the London - New York time difference will never be 6 hours.

The edge of a shadow is what shows the time on a time dial, not the center.

This cone and its conic section change with the seasons, as the sun's declination changes; hence, sundials that follow the motion of such light-spots or shadow-tips often have different hour-lines for different times of the year.

A sundial contains a gnomon, or a thin rod, that casts a shadow onto a platform etched with different times. As the sun changes relative positions over the course of a day, the rod's shadows change as well, thus reflecting the change in time.