Emerald Observatory is an iPad™ application which displays a variety of astronomical information. It is similar in that way to our flagship product, Emerald Chronometer®, but designed specifically for the iPad. Much of the supporting technology, including NTP (atomic time) and the highly accurate astronomical algorithms, was derived from Emerald Chronometer.
Emerald Observatory's time may not exactly match the time in the iPad's status bar because Emerald Observatory's time is synchronized with the international standard atomic clocks. This is usually accurate to about +/- 0.100 seconds. This is accomplished with the Network Time Procotol so it must have a Net connection to get a sync. If the Net is not available, it will fall back to the internal clock's value.)
It is also possible to change the clock's time and to animate it at very high rates. See Set Mode, below.
Animate the clock at one day per tick to see the Moon go thru its phases and size changes. Tap the phase button to see the times and dates of the quarters (New, 1st Quarter, Full, 3rd Quarter).
Animate at one hour per tick to see the terminator move around the world. Animate at one month per tick to see the seasonal changes.
The ring for the Sun is colored according to the Sun's altitude above the horizon at each time; sunrise and sunset are at the sharp boundary between red and blue.
Note that at high latitudes when the sun's altitude changes slowly the golden and blue regions will elongate.
See this effect by changing to a high latitude on the settings page and then animating by days or months.
If you try to determine the position of a planet with respect to the Earth by drawing a line from the Earth to the planet and on to the outside zodiac markings it will be only very approximately right because this display is grossly out of scale in distance from the Sun (and also in the relative sizes of the planets).
The best rate for animating this display depends on which planet you're concerned with; the inner planets move much faster than the outer ones; days works best for Mercury or the Moon, years for Saturn. If you animate by years you'll notice that the Earth jitters a little. That's not a bug. It's because we're advancing by exactly one calendar year but the Earth's orbital period is about 365.25 days. So the Earth gets a little ahead for three years and then jumps back on the leap year.
"Set" then changes to "Reset" and two sets of buttons labeled with time units appear on either side:
The blue ones on the right move Emerald Observatory's time forward by one unit; the red ones on the left move it in reverse. The "phase" buttons change to the time of the next or previous quarter Moon (you can then read the time and date from the main display). Tapping Reset changes it back to "Set", exits Set mode, restarts the clock, and hides the other buttons.
Press and hold any of these spots to advance continuously. Slide your finger off the button before raising it to "latch" the button and advance continuously. You can have more than one button active at once. Tap "Reset" to the return to the present time. The range of allowed dates is 4000 BCE through 2800 CE.
When the displayed time is not the current time a red label appears at the top of the screen showing the displayed time and its offset from the current time.
The familiar small "i" in the lower right corner flips the display to a settings and help screen.
The first switch controls whether Emerald Observatory will use the iPad's builtin location finding hardware.
For those situations where that is not sufficient (eg. a WiFi-only iPad not near a registered WiFi node) you can turn the switch to OFF and enter your own values for latitude and longitude. Enter the values in decimal format with negative numbers for west longitudes and south latitudes.
The second switch disables the iPad's automatic sleep mode. This is handy when the iPad is connected to a power source but be careful with it when running on battery.
The lower half of this screen is a brief summary of the app's capabilities.
