The Fourth Day
The Fourth Day is an astronomical clock and almanac for your iPhone or iPod Touch. Customized for your location using location services, or user entered latitude and longitude, The Fourth Day displays data about the daily, monthly, and yearly astronomical events related to time keeping.
Setting your Location
The Fourth Day uses your current latitude and longitude to calculate the local times of certain astronomical events. You can set your location manually by entering your latitude and longitude, or by using location services to determine your location for you. Note, that your exact location is not required. Generally for rise and set times, an accuracy of a few kilometers (or miles) is all that is necessary.
If your device has location services enabled, touch the "Location Svcs" selector as shown at right. The "Locate" button then becomes visible. Touch the Locate button and your GPS, wireless, or cellular network data will be used to determine your approximate location. Touching locate multiple times will improve the accuracy of your fix.
To manually set your latitude and longitude, touch the "Manual Entry" selector. This hides the Locate button. Now touch either the blue latitude display or the longitude and a spin wheel will appear as shown at right that will allow you to manually set your latitude or longitude.
Using the Clock Function
The Clock display shown at right displays a rotating earth with the daytime and night time sides highlighted. Touching the info button in the upper right hand corner of the screen flips the display to reveal options for the clock and other almanac displays.
The Daily Almanac is divided into two columns displaying both solar and lunar rise and set times. Astronomical, Nautical, and Civil twilight start times are listed before sunrise, followed by the local solar transit time (when the sun is highest in the sky). These times are displayed in your local time zone as set by your device. The time of sunset is followed the times of civil, nautical, and astronomical twilight end.
The right column shows moon rise, transit and set information. Unlike the sun, on which our day is based, the moon may actually set before rising again later that day, or may even transit before setting, and then rising again before midnight.
The Lunar Almanac is fairly straightforward. All times are displayed for your local time zone as set by you iPhone or iPod. Perigee is the time when the moon is closest to the earth in it's orbit, while Apogee is when the moon is at it's furthest distance. The difference between these two locations can cause the moon to appear slightly larger or smaller, and can to some degree influence the strength of tides.
The times of solstices and equinoxes do not vary with location. Note that the earth is at Perihelion (closest to the sun) during the northern hemisphere's summer season. The shortest and longest days also do not necessarily fall on the days of the Solstice or Equinox.
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