Monday, March 1, 2010

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!


  1. Wonderful to hear that StarPilot on the iPhone is coming soon !

  2. Thanks for visiting sailandoar. I was pretty pleased to hear that StarPIlot was on the way for these platforms too. Interesting that you, like me, focused on the iPhone. Luis, the developer expects that the iPod Touch will be a popular platform for StarPilot. I suspect he might be right.

  3. Hello All,

    StarPilot for the the iPhone/iPod was released by apple into the itunes app store yesterday (March 3). You will find a link the app on the starpilot web page at

    You might also check out our iNA app for the iPhone/iPod if you only need alamac data. Here is the link to that

    Take care.


  4. I just installed starpilot for iphone and am wondering if there is an error or if I am inducing operator error.
    I have been working through the problems in "Celestial Navigation in the GPS age" by John Karl. Page 61 spica reduction seems correct in that I have worked it by hand and get the same results. Starpilot get different results.
    Book (and me) intercept 5 away (min or MN) A = 86 degrees
    Starpilot intercept 19.6 away A = 86.3 degrees.
    While the A numbers are reasonable the intercepts clearly are not.
    I am sure I have miss used the program but I can not figure out how...
    Any ideas?

  5. So Luis from has set me straight. Like the dope I am I input DR (becouse the program asks for it) and not AP like the book problem is calculated from.

  6. So now that my issue is resolve, and proven to be oporator error (ME!) as I suspected, this thing is great! I have been doing celnav math via a calculator as shown in Celestial Navigation in the GPS age for years. I have been lusting over the Starpilot program but could not justify the expence. Being that I own an iphone the program was only $80 give or take. And I was sold! Just did most of the problems in the book in about an hour! Think about this: the low end ipod touch is $199 and the app is 79.99. The almanac is 29.99. I think I'm going to get an ipod to keep with my sextant in the case.

  7. G'day Tom,
    All three of your comments happened whilst I was away flying I think!!
    Glad that Luis resolved the issue for you. Whilst beta testing I made that error - working known problems - the first time, but I'd used the calculator version so I was aware of how to resolve it.

  8. Hello All,

    here in the US you can purchase an iPod touch at for $177. Here is the link

    This means that for $256 ($177+79) you can have the best piloting and navigation computer in the world which also happens to play your music and videos and run any of the 150,000 apps in the itunes store.

  9. And while on tiger direct you might also look at this very cool arm band for the ipod

    The Belkin F8Z523tt064 iPod Lillian Touch Dualfit Armband is a ultra-comfortable armband is hand-washable and water-resistant. It gives you full-protection and easy navigation access to your iPod, while minimizing the bulk on your arm.

    This means that you can have the iPod attached to your body while doing your sights for on the spot sight reductions and fix computations.

  10. Hello All

    StarPilot training videos are now available at

  11. Any chance of getting a droid app for this program?

  12. G'day Joseph, thanks for dropping by. I suggest you go to and ask the question there. That is the developer's site.

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