A while ago, I wrote an article for the newsletter of the local astronomy organisation. They apparently decided not to publish it, although they never told me why not. I figured I might as well post it here. Some of the prices and details may well be out of date, if not, they will be eventually. And other choices will no doubt come along. Caveat emptor.

Astronomy with an iPod
Owners of an iPhone or iPod Touch have a surprisingly powerful astronomical tool at their fingertips.

These days the Apple iPod is almost ubiquitous; it seems like almost everybody has one. Its latest incarnations, the iPod Touch and iPhone, have been a runaway success since their introduction only two years ago. Now, you might think this has very little to do with astronomy, wouldn't it be nice if there was a way to make this convenient handheld device useful for our hobby? A staggering amount of applications (or "apps", as Apple likes to call them) have been developed for it, ranging from utterly nonsensical to innovative and surprisingly useful. And that includes the astronomical software section...

As with all iPhone applications, it pays to do a little research before spending money. For example, there are quite a few applications that'll show NASA's excellent "Astronomy picture of the day", the most expensive of which costs £1.79. A small amount of money, but still staggering considering you can use the device's built-in webbrowser to see that same image for free!

However, there are some real gems to be found as well, if you're willing to dig just a little deeper.

For example, there's Julian James' "Moon Atlas" (£3.59) offering current phase and libration of the Moon as seen from any location on Earth, with the usual pinch/scroll controls and an overlay to identify craters and other surface features.

Then there's iEphemeris (and iEphemeris Pro). The "lite" version has its functionality limited to the ephemeris of the Moon, whereas the "Pro" version also offers sunrise/sunset. It also suffers from a timekeeping bug on some platforms, but at least it's cheap at £1.19.

"GoSkyWatch" (£3.49 at the time of writing) is a basic planetarium app with mixed reviews. It illustrates the need for Apple to introduce a "try before you buy" option on applications, since I, like some other reviewers, couldn't even get it to work!

"Earthview" (£1.19) is a pretty application, showing which parts of the globe are sun-lit or in darkness. It's quite satisfying to spin an entire planet with your finger, and hidden behind a second screen there's a handy sunrise/sunset calculator which understands astronomical twilight. Recommended.

However. Sticking with head and shoulders above all other apps is StarMap, by Frédéric Descamps (http://www.star-map.fr/). It comes in two flavours, a basic "StarMap" for £5.99 and "StarMap Pro" for £11.59. While that may seem pricey at first, it turns out to be a surprisingly fully-featured astronomy package.

I initially purchased the basic version, which looked like it would do enough for my needs, with 110,000 stars up to magnitude 10, planets and their satellites, 110 Messier objects and an "at a glance" overview of the night's sky as well as handy features such as "night vision mode" (which turns the screen red) and a torch (which makes the entire screen bright white, with a slider to adjust brightness).

However, once I started exploring this piece of software, it quickly became apparent that it would come in really handy while observing, and that I would need more than just 110 deep-sky objects.

Thankfully, the Apple Store people were friendly enough to give me a refund when I ticked the box "software purchased by mistake" on their support site. An annoying hoop to have to jump through, because there's no concept of "upgrading" (or "try before you buy", as I mentioned earlier). But at least now I could justify getting the full version.

This, Starmap Pro, comes with no fewer than 2,500,000 stars, or the entire Tycho 2 catalogue up to magnitude 16; as well as the full set of Messier (with images), NGC and IC objects. It also lets you define telescope optics to overlay a field of view, something the basic version lacks.

And it's a joy to use. Navigating the night sky couldn't be easier, scrolling around with your finger, and pinching the screen to zoom in and out as in any other application. Small gripes include the clunky lists to search for NGC and IC objects, the difficulty of fine control with cold fingers at the telescope, and a lack of a function to plan a night's observing. But these are minor quibbles, considering just how powerful an application it otherwise is. It can do nearly everything you might want from a planetarium package.

And that means I don't need a star atlas at the telescope anymore, just the iPod. And that's not bad going for what started life as a music player...