🕰️Sundial Designer - Horizontal, Vertical and Equatorial Hour Lines, Printable Template

How to use Sundial Designer

1. 1Choose the dial type and a city, or enter latitude, longitude and time zone; for a vertical dial set the direction the wall faces
2. 2Adjust the nodus height and toggle half-hour lines, declination lines, the analemma or longitude correction
3. 3Set a date and clock time, or press Play to watch the shadow move through the day, and read the corrections beside the dial
4. 4Pick a diameter, download the SVG or print it, cut out the gnomon triangle and stand it on the substyle line

FAQ

Why are the hour lines on a horizontal sundial not 15° apart?

The Sun moves 15° per hour around Earth's axis, so the shadow turns evenly only on a dial plate perpendicular to that axis (an equatorial dial). A horizontal plate is tilted to the axis by your latitude φ, and projecting even hour angles onto it gives tan θ = sin φ · tan h: lines crowd together around noon and spread out in the morning and evening. At the equator the lines nearly coincide; at the pole they become even 15° steps again.

How should the gnomon be set up?

The edge of the gnomon that casts the shadow (the style) must be parallel to Earth's axis, pointing at the celestial pole. On a horizontal dial it rises at an angle equal to your latitude along the noon line toward true north (true south in the southern hemisphere); on a south-facing wall it makes 90° − latitude with the wall and points down. For other walls the tool gives the style height and substyle direction. Level the plate and align it to true north, correcting for magnetic declination.

Why is my sundial 10–20 minutes off my watch?

A sundial shows local apparent solar time, while a watch shows zone time. Three things separate them: the longitude correction of 4 minutes per degree from the zone's central meridian; the equation of time, because Earth's elliptical orbit and axial tilt make the real Sun run up to about 14 minutes slow in mid February and 16 minutes fast in early November; and an hour for daylight saving. The tool lists each term and converts both ways.

What are declination lines and the analemma?

The shadow of one point on the gnomon, the nodus, traces a curve across the dial during a day, and the curve depends on the Sun's declination: the solstices give two hyperbolas and the equinoxes a straight line, so the nodus shadow also tells the season. If you mark the nodus shadow at the same clock time every day, for example 12:00, the marks form a figure-eight analemma whose width is the equation of time and whose height comes from the changing declination.

How does an equatorial sundial work, and why no shadow in winter?

Its plate is parallel to the equator and the gnomon passes straight through it toward the celestial pole, so the hour lines are an even 15° per hour, the easiest dial to make. The catch is that the Sun lights the upper (pole-facing) side only between the March and September equinoxes and the lower side the rest of the year, so both faces need hour lines, mirrored on the underside, and near the equinoxes the Sun grazes the plate and the shadow is hard to read.