Sundial — Solar Time

A sundial on your phone: the dial for where you are, the shadow where it falls
right now, and the time the Sun keeps.

THE DIAL IS YOURS

The hour lines of a horizontal dial are not evenly spaced, and how uneven they
are **depends on the latitude**: at the equator they collapse onto noon — a
horizontal dial does not work there at all — and towards the pole they open out
to a clean fifteen degrees an hour. The app redraws the plate for the place you
are in, and that is the thing worth seeing rather than reading.

The shadow falls away from the Sun, as long as the cotangent of its altitude:
enormous and soft at dawn, short and hard at noon. At night there is none, and
the app says so instead of drawing a fake one.

WHY IT DISAGREES WITH YOUR PHONE

Three reasons, all of them real:

• **Longitude.** A time zone is an hour wide: away from its central meridian
the Sun is early or late by up to half an hour.
• **The equation of time.** The Sun is not a uniform clock: it runs up to a
quarter of an hour fast or slow over the year.
• **Summer time.** A whole hour of it.

The app shows the difference rather than hiding it, because it is the first
thing anybody asks a sundial.

WHAT IT DOES NOT DO

• No account, no sign-up.
• No servers: your position never leaves the phone.
• No network to work — everything is computed on the device — only for the ads.
• No precise location and no background location: a kilometre of longitude is
four seconds of solar time.

And if you would rather not give a position, a list of cities is bundled with
the app.

PERMISSIONS

Coarse location. Internet, only for the ads that keep the app free.

Privacy policy:
https://mindcontact.app/mcma-sundial/privacy/

Recent changes:
First release: the dial for your latitude, the shadow, and the gap to the clock.