Science First
®
/
STARLAB
®
• 86475 Gene Lasserre Blvd, Yulee, FL 32097 USA
800-875-3214 • 904-225-5558 • FAX 904-225-2228 • www.starlab.com
12
You can change the way time is flowing using the following controls in the toolbar.
Click “Single Step Backward” to move the time back by one time step and then freeze it.
Click “Backward” to run time backward continuously. Each time the screen is updated, the
time moves backward one time step.
Click “Stop” to freeze time at the current value.
Click “Forward (Play)” to run time forward continuously. Each time the screen is updated,
time moves forward one time step. This is the default time flow mode.
Click “Single Step Forward” to move the time forward by one time step and then freeze it.
If you want to view the sky at a specific time, first click the “Stop” button, and then type in the
viewing time. If you type in the viewing time first, the time shown onscreen might update before you
press the “Stop” button.
There are three short cut keys that play and stop time:
.
The period key (.) stops time
/
The slash key (/) means routine forward
,
The comma key (,) runs time backwards
Software Operation
2. Discrete Time Steps
Discrete time steps move the time by a specific increment every time Starry Night™ updates
the display. Discrete time steps are often useful when you’re watching astronomical events. For
example, if you wanted to see how Jupiter’s position changes over the next few months, you could
set the
time
to 9 PM in the evening and then set the
time step
to one day. Starry Night™ would run
time forward, showing the sky at 9:00 PM each night. If you had chosen a multiple of real time
instead of a discrete time step, you would see an alternating cycle of day and night, instead of seeing
the sky at the same time each night.
Some of the discrete time steps listed in the menu might be unfamiliar:
•
Sidereal day
: This is the time it takes for Earth to rotate once on its axis. It is four minutes shorter
that the day we are familiar with, the solar day. Sidereal and solar days differ in length because of
the revolution of Earth around the Sun.
•
Lunar month
: This is the time between two full moons, as seen from Earth. It is about 29 days.
C. Customizing Time Steps
You are not limited to the time steps that appear in the time step pull-down menu. If you click the
numerical part of the current time step, it lights up and you can type a numerical value. This will let
you change the time step from one day to seven days, for example.
