Celestial Navigation - With an iPhone Touch!

How many of you have got one of these? How many of you use it? I'm very fond of my Cassens & Plath. It's both a connection to the past and a thing of today. It's accurate and it doesn't rely on satellites. It also gives me a huge kick every time I reduce a sight and draw a line of position on the chart.

My problem is that I hate paying money to somebody for the tables and the almanac. I keep forgetting to make sure that they are up to date and they always seem to disappear just when I want them.

For some years now I've been using StarPilot for the Texas Instruments TI-89 Calculator. It's simple and robust and has a heap of functionality. But as with most calculator applications it's limited by the calculator interface. The calculator interface is not what you'd call modern!

The solution is at hand however. For the past couple of weeks I've been testing StarPilot for the iPhone and for the iPod Touch. It's brilliant! The functionality is much the same as the calculator version but the interface belongs very much to 2010.

I'm not going to do a detailed review right now. But just a brief run through. A more detailed review will follow.

When you first start StarPilot you need to enter some data in Settings. Things like your DR position, the ZD and Watch Error and the Date. In addition you enter IE for your sextant and Height of Eye. Once you've done that StarPilot is basically ready to go. First step is probably to compute the sky so that you know what sights are available. You can project forward to a future time and indeed you can also compute the sun and the twilights so you have a good feel for the time that you want to compute the sky for.

Having computed the sky you get a plot of the sky with a series of "triads" which you can cycle through. Each triad consists of three sights with suitable azimuths. Touching any of the celestial bodies brings up details - name, Hc and Zn - I've done that for Betelgeuse. In use it makes a very good star finder. You can also list the bodies and their ephemeris data in text form.

Having shot your bodies you then choose Sight Reduction. For each sight you simply need to pick the body from a searchable list and enter the Watch Time from a time picker and the Hs. StarPilot calculates Ho and reduces the sight - it's fast and simple. Once you've entered the first WT StarPilot offers that as the first choice for your next sight.

Once you've entered a set of sights you can use StarPilot to produce a fix - based on your DR and speed/course parameters. Fixes can be arrived at by plotting or by computation.

There are also a bundle of useful utilities in StarPilot for calculating things like the Sailings - either Rhumb Line or great Circle, distance off, set and drift, wind and a range of utilities for things like UTC by Meridian Passage and the one I like: UTC by Lunar Distance.

If you are stuck at home, away from the sea, there's no better test of your skill with the sextant. Shoot a few Lunar Distances and you'll really find out how good you are. This particular process dates from the time before time - at least the time before reliable chronometers. Through a time consuming process of calculation - called "clearing" - you can derive your time from the distance measured between the moon and another celestial body. StarPilot takes the grind out of the calculation. You just have to measure an accurate Lunar with the sextant and enter the data. Great fun and a test of skill.

This is the quickest of overviews of StarPilot on the iPhone/iPod Touch. There is so much more there. What I would urge you is if you are a celestial navigator, a user of StarPilot on the calculator or if you have always hankered to use a sextant then check out StarPilot. It will be in the App Store in the next few days. There is no other application like it as far as I can determine in the App Store. It's brilliant.

When I've a little more time I'll write up the step by step process of using StarPilot. Until then get a copy for yourself and have fun!