1
What is StarTrak? What does it do?
StarTrak
is a computerised database, containing information on the planets, all the Messier objects, as well as a number of other objects in the sky. For any object in its database, StarTrak can give you that object's position, described in- RA/Dec coordinates, and also in
- Altazimuth coordinates, i.e as a number of degrees and minutes upwards from the horizontal (i.e. an altitude angle) and a direction in degrees and minutes from true North (i.e. an azimuth angle). Thus, if your telescope has either RA/Dec setting circles or azimuth and altitude setting circles, it's easy to point the telescope at the object of interest.
Figure 1.1
Figure 1.1 shows a typical screen of information on a Psion computer running StarTrak. It shows three alternative names (M31, NGC224, Andromeda Spiral) for the same object, together with other information. If you were running StarTrak now, looking at the Andromeda Spiral, it's very unlikely that the altitude and azimuth readout would show the same values as in figure 1.1 - in fact, as the Earth spins on its axis and orbits the Sun, the altitude and azimuth of any celestial object are constantly changing. StarTrak updates its altitude and azimuth readout every second. It can do this because it knows the current time (from the Psion's clock), and from this can calculate the Earth's position in space; StarTrak also knows the latitude and longitude of your chosen observatory, and the RA (Right-Ascension) and Dec (Declination) coordinates of each celestial object in its database. StarTrak is programmed to use this information to calculate an object's altitude and azimuth (as seen from your chosen observatory), and to keep re-calculating the altitude and azimuth, which change with the passage of time as the Earth moves through space.
StarTrak
doesn't display a view of the night sky, and is not intended to replace star charts. Rather it is designed to be used with a star chart to help you find the object of interest: point the telescope in the right direction with information from StarTrak, and compare the view through the telescope with your star chart to identify the object of interest. Of course, in many cases it will not be necessary to use a star chart - from the view through the telescope, the object you are seeking will be obvious.The present version of StarTrak doesn't show the positions of the Sun, Moon, asteroids and comets.
The present version of StarTrak ignores
- atmospheric refraction
- precession (this is the gyration of the Earth's axis over a period of 26000 years, caused by the gravitational effects of the Sun and Moon), and
- nutation (the slight wobble in the Earth's movement caused by the variation in the relative positions of the Moon and Sun)
since these effects cause only a fraction of a degree change in apparent position.
Navigate through the Psion's System screen (using the arrow keys at the bottom-right of the keyboard), and you will see StarTrak listed under the opl programs. Use the arrow keys to move to the name StarTrak, and press the Enter key (right-hand side of keyboard). This will start StarTrak.
Esc key
One of the most useful keys (if you make a mistake partway through some operation in StarTrak) is the Esc key (at the top left of the keyboard). If you press the Esc key partway through some operation in StarTrak, this will abandon that operation.
Menu key
When StarTrak is running, if you press the Menu key (bottom-left of keyboard), a menu of options will appear on the screen (figure 1.2):
Figure 1.2
After pressing the Menu key, you can navigate your way through these options by using the arrow keys (left, right, up and down-pointing), found at the bottom-right of the keyboard. As you press each arrow key, a different menu option will be highlighted; when you reach the desired menu option, press the Enter key (right-hand side of keyboard) to select that option. If you decide that you don't want any of the menu options, press the Esc key. If you have used other application programs on the Psion, you will be quite familiar with this use of the Menu key.
You will notice that the menu options are in three groups - 'Observatory', 'Object' and 'Special'. The 'Observatory' group includes options for setting the locations of observatories, and for selecting one for your observing session. The 'Object' group contains options for selecting a celestial object for viewing, or for adding a new object, or editing the details of an existing object. The 'Special' group contains further options described elsewhere in this manual.
If you wish to exit from StarTrak to access another application on the Psion, select Exit from the menu options. (It may be the case that the Exit option has been disabled - for example, if the Psion is shared by members of an astronomy club, whose only use for the Psion is the StarTrak program. You can enable or disable the Exit option by an option found under the 'Special' menu group.)
If you simply want to switch off the Psion, do this in the normal way, that is, while holding down the key at the bottom-left of the keyboard, press the OFF key (second key along the top row of keys). When you switch on the Psion again, it will resume StarTrak, using the same settings (for observatory, timezone and celestial object) as previously.
To conserve battery power, the StarTrak program can be set to automatically switch off the Psion after a definable period of time. You can access this functionality via Auto Powerdown in the 'Special' menu group.
If the Psion screen goes blank suddenly, this is a sign that it has automatically powered down. To resume use of StarTrak, press the ON key, and type the computer's password (if any).