Pocket Sundial

Get a solar powered clock right on your phone! Get back to our roots and tell time like our ancestors did: with the sun. Available on iPhone, iPad, and iPod Touch.


Pocket Sundial on iPhone
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Useful

Tick Tock

Frankly, who couldn't use a solar clock? It never needs batteries... Honestly, though, an understanding of a sundial leads to a better understanding of our world.

Track the Sun

Tick Tock

We know the sun rises and sets, but modern humans tend to lose touch with the more subtle changes to the sun's path across the sky throughout the year. Move the sundial ahead or back in time to find out what happens.

True Solar Location

Tock Tick

This App is no joke! Based on your location and the local time, this app computes the location on the sun based on the Earth's orbit. From the sun's location, it determines where to draw the gnomon's shadow.

Sundial Directions

Getting Started

Sundials rely on your current location, so it is easiest if you allow the app permission to find you. If not, though, you can also manually choose your location from a map accessed through the info button.

Compass Bearings

The compass has three settings, allowing you (as near as I could imagine) full control, since, frankly, the compasses in these devices aren't perfect. With the compass 'off,' you are tasked with finding (true) North and orienting your device accordingly. With the compass set to 'assist,' it will indicate North, but you are in charge of turning your device. 'Auto' mode will turn the sundial for you, keeping it pointing in the correct direction.

Playing with Shadows

One fun part of this app is how realistically the shadow will react to your motion. This is where that mysterious "[ ]" button comes in. If the compass is in 'Auto,' clicking this button locks the orientation of the sundial on your device. Now it is like you're holding a real sundial, because if you turn it so that it is no longer facing North, the sundial doesn't work right. Just like spinning a real sundial, the shadow will move around with no regard for the hour lines.

If you have the full version, the gyro can be turned on to take this a step further. Now, if you tilt the sundial side to side, the shadow will react to that, too. So make sure to hold it flat (or not!)

Changing the Time and Place

At the top of the main view are four important pieces of information: the time, date, latitude, and longitude. These can be changed by clicking on them. A slider will appear, and by moving it to one side, the value will increase (and to the other side the value will decrease). For instance, by clicking the time and moving the slider just a bit to the right, minutes tick by in seconds. Move the slider further, and the hours fly by. Where will the sun be next?

To reset the values of any of these, merely click the button instead of the slider. This brings it back to the current time, date, or location.

Latest News

August 2010: Pocket Sundial Released

November 2010: Pocket Sundial Lite

January 2011: iPad version released

Sundial Links

General

  • North American Sundial Society: Sundial news, publications, and experts. Just imagine the parties!
  • British Sundial Society: For those of us with a more easterly longitude!
  • Giant Sundial: Pictures of a particularly large sundial. About as far from a Pocket Sundial as you can get.
  • Watches Back in Time: A nice - and very complete - list of sundial links. Learn tons! (Thanks to some students in Colorodo for suggesting this one!)

The Math of a Sundial

  • The Mathematics of Sundials: a comprehensive project from students at the University of Singapore. THis breaks down the types of sundials
  • Analemmatic sundials: this site gives a great description of the math of the sun's shadows, from the analemma to the trigonometry. To be noted, though, it focuses on a specific type of sundial - the one represented by the stick gnomon in the Pocket Sundial.

The Sun's Strange Path

  • Sunrise/Sunset Algorithm: Finding the sun isn't as easy as you might expect. Sure it goes up and comes down, but to actually predict the shadow on a sundial, we need to know its position precisely. For a peek under the hood, take a look at the algorithm I used.
  • How to Compute Planetary Positions: a well written document detailing how to find the sun. It involves plenty of steps, specialized vocabulary, and coefficients. As the name implies, you can also learn how to compute the position of the planets.
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