Time Screen

• Some functions within Asteroid PRO require the setting of a date and time. For example, to follow an individual asteroid in its orbit requires the setting of an initial date/time. The Time Screen is invoked automatically at times to prompt for a date/time and usually can be invoked by a pull down menu under the menu label, Observer, from many screens. However, it is useful to note that the primary date/time setting is set implicitly by the Search for Occultation function which determines the date and time of an occultation from a user set month range.

• When needed the time is date and time can be entered directly in the upper center of the screen. The default interpretation of the time is that it is UT but provision is made for TDT and Local times when more convenient. Local requires the selection of a site from the Location Screen (and the setting of its hour difference from UT).

• The Now and Midnight controls use the internal computer clock to set the date/time, exactly or with the hour/min/sec zeroed as in the previous midnight from Now.

• When moving the asteroid along its orbit in ephemeris mode, it is possible to step the time by user specified increments. The increment is set by selecting which date/time element needs changing and the amount of that change and the number of time steps to take using the increment. The bottom half of the screen shows the selected date/time and various additional time values associated with the set date/time. For example, the Julian Day, the UT, the Julian Ephemeris Day and Ephemeris Time is noted along with Greenwich Mean Sidereal Time and Local Mean Sidereal Time. Delta T, ET - UT, is also shown in seconds.