Chapter 2

StarTrak needs to know the difference in time between the Psion's clock and Greenwich Mean Time (GMT) which it uses for its calculations. For example, if you observe from California, and your Psion is set to local time, this is probably 7 or 8 hours behind GMT (depending on whether you are using daylight saving time). You can find out what the current GMT is in a number of ways: if you have access to the Internet, a very accurate GMT readout is available at http://time.greenwich2000.com/. Alternatively if you have a suitable radio receiver, tune into BBC World Service, which gives the time in GMT each hour.

When you know the time difference between your Psion's clock and GMT, access the GMT option in the 'Special' menu group. This allows you to set the number of hours by which your Psion's clock is ahead of or behind GMT. To select 'ahead of' or 'behind', use the left or right arrow key to toggle this field on the display. Then use the down-arrow key to move to the numeric field, where you can set the number of hours. Finally press the Enter key to submit this information.

StarTrak will remember this time difference (even when the Psion is switched off). It will stay the same until you change it.

Please note that for accurate use of StarTrak, your Psion's clock should be set accurately. Setting the Psion's clock is described in the Psion documentation, which came with your computer.

‘Real’ time and ‘Fixed’ time

Usually you will be using StarTrak in ‘Real’ time mode, that is, StarTrak displays information on an object as it is when you observe it. Sometimes you may want to ‘fix’ the time and date to something other than the present - for example you may want to ask the question "Is M13 visible at 23.00 tomorrow night?". For this you can fix the date and time, using the Real/Fixed Time option in the ‘Special’ menu. You can fix the time and date anywhere between 00:00:00, 1^st Jan 1970 and 23:59:59, 18^th Jan 2038.

To define an observatory in StarTrak, select Add/Edit from the 'Observatory' group of menu options. This will first ask you for the name of your observatory site (figure 2.2). The observatory name will be preset to the name of the current observatory (which will be the Institute of Astronomy, Cambridge, England, the first time you use StarTrak), but you can overwrite this with the name of your chosen observatory. (In the example shown in figure 2.3, we assume that the preset name has been overwritten with the name 'Brook Farm'.)

StarTrak then asks you to provide the latitude and longitude (figure 2.3). Note that you define the latitude and longitude in degrees and decimal parts of a degree (since a decimal fraction is generally easier to estimate from a map rather than minutes of a degree).

Select 'Yes' to the question 'Commit this data' and press Enter.

You can define any number of observatories in this way. You can also use the same menu option to edit the details of an existing observatory, and you can use the 'wildcard' asterisk character (to save typing) to select an existing observatory. For example, if 'Brook Farm' is an observatory in StarTrak, 'B*' will select this observatory).

When you have a few observatory locations stored in the StarTrak database, you can choose the appropriate observatory using the Choose option from the 'Observatory' menu group. This will ask for an observatory name (and will be preset with the name of the current observatory, which you can overwrite by typing the name of another observatory). Remember that when you are typing the name of an observatory known to StarTrak, you can use a wildcard character (an asterisk) to save you from having to type out the full observatory name.

You can ask StarTrak to show you a list of the observatories stored in its memory. To do this, select the List option from the ‘Observatory’ menu. You will then be prompted for a ‘wildcarded’ observatory name, for example,

will list all the observatories, b* will list all those beginning with ‘b’ (or ‘B’), and so on. When you have a list of observatories on your screen (up to 6 can be displayed on one ‘page’ of screen), you can press Enter for the next (or previous) page of matching observatories. You can use the up or down arrow keys to move to a particular observatory, and press Enter. StarTrak will then display the details and position of the current object as seen from that observatory. This gives another way of choosing an observatory, in addition to the method described in the previous section.

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Chapter 1

Chapter 3

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