5. Press MODE to return to the Tour list. Press the Scroll keys to scroll through the
list. Press ENTER when you find the next object you wish to observe.
6. Press and hold down MODE for two seconds to leave the Guided Tour menu.
Other Guided Tours are available, such as "How Far is Far" and "A Star's Life." If you
have programming skills, you may wish to create a custom Guided Tour. See
CREATE
YOUR OWN GUIDED TOUR
, page 56.
The
Global Positioning System
The Global Positioning System (GPS) is comprised of 24 satellites orbiting
the Earth that are constantly transmitting their precise position and time.
The system provides highly accurate, worldwide positioning and navigation
information for any number of applications.
GPS receivers on the Earth acquire signals from three to twelve satellites
to determine the precise latitude, longitude, and time of the receiver.
(Accuracy of the receiver's position may be within 10 to 15 feet.) As
Autostar II uses latitude, longitude, and time information to calculate the
positions of celestial objects, GPS is an ideal tool for aligning your
LX200GPS
telescope.
Detecting True Level
To detect level of the base of the telescope, Autostar II must calculate the tip
and tilt of the telescope at three compass points and then compensate for it.
Finding level involves the geometric calculations of a "plane." In order to
define a plane, three positions are necessary. This is not unlike building a
table: For a table to stand level and solid, it must have a minimum of three
legs. Autostar II makes gravitational measurements to make a precise deter-
mination of true level.
Finding True North
Locating True North is one of the most important ingredients in the alignment
of a telescope. True North is the axis—the pole—which the Earth spins about
and is a key reference for the motion of the Earth.
As you look at the night sky, the stars seem to move; in fact, if you watched
long enough or took a long time-exposure photograph, you'd realize that the
stars seem to revolve around one point—the pole or True North. When
Autostar II knows where True North is and also knows the time, it can calcu-
late the location of all the other objects in the sky.
One traditional way to find True North is to locate the North Star, Polaris,
which lies very close to True North. Another way to calculate True North is to
use gyroscopes or accelerometers.
The
LX200GPS
determines True North by using a magnetic North sensor. The
sensor locates magnetic North. Magnetic North is not True North, but a
measurement of the magnetic lines of the Earth. Magnetic North may devi-
ate several degrees from True North. But Autostar II, using the observation
site location determined by the GPS and magnetic North information, can
calculate the position of True North.
Some areas are subject to magnetic disturbances, and the magnetic field of
the Earth changes slightly from year to year. Autostar II allows you to adjust
for discrepancies in the local magnetic field using the "Calibrate Sensors"
option in the Telescope menu. See page 29 for more information.
21
LX200GPS INFO
Fig. 14:
LX200GPS
GPS Receiver.
GPS
Receiver
