The input is a latitude, longitude, date, and finally a time. Then StarPilot searches for sun and moon, then it searches through the stars, starting with the brightest and working down. Generally you can stop at about magnitude 2.0 (stars about as bright as the Big Dipper stars) by pressing the Exit key or if you want only the very bright stars, stop earlier. Then it starts to search the planets and then it plots out the sky as you see at the top of this page. It takes about 4 minutes to compute the sky to the magnitude 2.2 level shown above, including the moon and two planets. Just bright stars is quicker.

You can also set Hc min and max (default 0° and 90°) if you wish to limit the display. Generally stars right overhead and those very near the horizon are not as reliable for celestial fixes. Hence for a cleaner display you could limit the view to, say, >10° and <80°, although we have not set these limits in this example. The graphical output display is a radar-like view of the sky, with you in the center. Top of the screen is North, to the right is East. The center of the circle corresponds to directly overhead, Hc = 90°, and the circumference of the circle is the horizon with Hc = 0°. Between 0 and 90 the plot is linear, that is, one third of the way to the center is 30°, two-thirds is 60°. An object half way to the center would appear 45° above the horizon.

The sample shown above is for 47° 39' N, 122° 20' W on Oct 21, 1999 at 0500 UTC for stars equal or brighter than magnitude 2.2. To read specific values with the calculator, you would move the cursor (the "+" in the NW corner) over the object and then press Enter. To see very roughly how this works, position your cursor now over the object in the picture above and you can read the values you would get from the calculator: object name, magnitude (brightness), Hc and Zn — this takes a 4.0 or newer browser. Click an object here to see the USNO output for this sky — a valuable resource in its own right, if you did not know about it before. (Note we had to put the picture at the very top of the page so it would work properly with all, or at least most, browsers.)

To choose the best sights, look for 3 bodies that are: (a) nearest to 120° apart, (b) above 10° and below 80°, (c) bright, and (d) about the same height in the sky. Of these criteria, (a) is the most important. From the annotated version below we see that this sky has two nice options, the red lines or the green lines. All of the bright objects are highlighted in yellow, as is Polaris although it is not bright, just prominent. Three lines drawn at 120° with a Sharpie pen on a piece of transparency is an easy way to identify good triplets of sights.

Center is overhead, circumference is the horizon. Color annotations are not part of StarPilot.

This Sight Planner is a powerful and convenient feature of the StarPilot. It turns the device into a hand held planetarium that can be used to study the layout of all celestial bodies in the sky for various purposes — navigation in the middle of the ocean, or just checking out the sky before an evening walk at home.