Technical data

Chapter 3 Time 13
3. Time
The Time functions allow you to set the time and date, display the current time in a variety of formats, and select the
location from which you want to observe. You may select a time and date anywhere from January 1, 4713 B.C. to
December 31, 9999 A.D.. However, you would normally select dates that correspond to your planned observing
sessions.
If you set a date or time, Autostar Suite's internal clock is halted and all calculations will use your chosen time and
date. If you choose to use the system time, the internal clock will again begin running and will be accessed in real-time
as the system requires.
When Autostar Suite is communicating directly with an observatory, the observatory will provide an accurate time
source for Universal Time (UT1). When not connected, Universal Time is derived from the internal clock of the PC.
Time Display
The Time Display function displays a modeless dialog box that allows you to continuously monitor all of the current
times required by Autostar Suite. Since the Time Display is modeless, you may keep the display active while using
other program functions. The display can be disabled either by selecting the Time Display menu item, or by double
clicking the left mouse button on the symbol in the upper right corner of the display.
The first time display is that of the Local Zonal Time for the currently selected location. If Autostar Suite is not
connected to an observatory, this value is derived from the internal clock of the PC. The current status of daylight
savings time is shown below the Local Solar display.
The Local Mean Solar Time is the actual local time based on the mean position of the sun. This time, plus the value
of the Equation of Time yields Local Apparent Solar Time, which is the time indicated by a sundial at the current
location.
The Universal Time display shows the value of the time at Greenwich, England. This is the precise time used in all
astronomical calculations. The time returned from an observatory will be its current value of Coordinated Universal
Time (UTC) corrected for its position. The corrected time is then called UT1. Observatories near the United States
will probably be using (UTC) derived from radio station WWV or WWVH (Hawaii).
If the Universal Time value reflects a time that is on a day different from the current local day, a warning is displayed
below the display indicating that fact. The message Next Day will be displayed if the UT day is greater than the
current day, and Previous Day if it is less. No message will be displayed if the UT and local days are the same.