GoSkyWatch Planetarium (for iPhone) is a bit different than most of the iPhone planetarium programs I've seen. One unusual feature is that at the center of the screen is a telescope feature (the view target) that highlights whichever object is in its crosshairs. Like the Editors' Choice Star Walk 6.0 (for iPhone) but few other similar apps, the sky appears correctly oriented no matter how the phone is tilted, rather than being restricted to portrait or landscape orientation that will slant the view if you're not holding it. On the downside, unlike most planetarium apps, it's limited to showing stars visible to the naked eye, which may lessen its appeal for any but the most casual observers.

I tested GoSkyWatch on an iPhone 5 . It also works with earlier iPhones, iPads, and iPods touch, provided they run iOS 4.3 or later.

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Night Sky
When you open the app and tilt the iPhone upward, you see a view of part of the night sky. By pinching the screen, you can see nearly the entire dome of the heavens, even the stars below the horizon, which are visible in the app through a green filter. By stretching you can zoom in on smaller sections.

When you come across an object of interest and move it into the view target at the center of the screen, a thumbnail image of it will appear. Tapping on the thumbnail (which I found tricky and often took more than one try) calls up information about the object. Although GoSkyWatch doesn't show planets at sizes corresponding to their brightness, like the Editors' Choice SkySafari 3 (for iPhone), it gives a numerical figure for the planet's magnitude for the current day (or whatever day the app's time is set to).

Settings and Controls
At each corner of the screen is an icon: Search (magnifying glass) to upper left; settings (gear) to upper right, date and time (clock) to lower right, and social (heart) to lower left. From Social you can e-mail screenshots, tweet them, or post them to Facebook. With Data and Time, you can show what the sky looked (or will look) like from the year 1 to 4000 AD. You can also set the time into motion and watch as the stars seem to rotate around the celestial pole in their diurnal cycle, and planets move along the ecliptic, but I found it rather tricky to control, compared with some apps that easily let you alter the rate at which time progresses.

From Settings, you can choose between three buttons. The wrench (preferences) lets you turn on or off different features: night mode (which turns the background red to preserve one's eyes' dark adaptation); show all DSOs (deep-sky objects: galaxies, nebulae, star clusters); star color; Milky Way; object images; daylight (which gives you a blue background); and various grids: ecliptic, horizon, celestial grid; constellation lines, boundaries, and images. For the latter, it shows a drawing of creature or other object represented by the constellation, for whatever constellation is centered in the screen. You can choose whether to depict Pluto as a planet or not, and more.

The second button in Preferences, Location, shows your latitude and longitude, and shows your position on a world map. The third button, About (a question mark), links you to the GoSoftworks site for a user's guide and support; to iTunes if you want to write a review, or to get another app, GoSatWatch, for satellite observation. There is no in-app Help functionality, though; you have to access the User Guide through the site. If you're out of range of an Internet connection, you're out of luck.

The fourth main button, Search, lets you select objects (planets, deep-sky objects, stars) from drop-down menus. It provides some basic information about the object, plus an image and viewing information. Unlike some apps such as Skymap (for iPhone), it will "beam" you straight to the object rather than having you navigate to it by following arrows across the sky.

Small and Sparse Stars
One downside is that the star images are relatively small compared with other apps, and they don't appear any brighter as you zoom in. It makes the sky look somewhat star-sparse, especially in a magnified view. Most planetarium apps reveal fainter stars as you zoom in.

A related issue that's potentially more problematic is that the app's view is limited to 8,000 stars down to about magnitude 6.5, roughly the brightness of the faintest stars that a keen-eyed observer can see from a reasonably dark sky. Although it shows deep-sky objects, many of them are faint and require a telescope or at least binoculars to spot. Without the ability to show their location relative to other fainter stars in a zoomed view, GoSkyWatch is of little to no use in locating them in such instruments.

An App for the Casual Skygazer
GoSkyWatch Planetarium has some nice features, like a view target that highlights whatever is in the center of the screen, generously sized image thumbnails, and the ability to keep the sky correctly oriented, even when not held in portrait or landscape position. It gives precise figures for planetary brightness (magnitude), though it doesn't show planets at sizes relative to their brightness.

A big limitation for many people beyond the most casual skygazers is its inability to show stars fainter than naked-eye visibility. This may be fine for very casual observers, but if you turn even the most basic pair of binoculars to the sky, many more stars will spring into view. Other planetarium apps we've reviewed, including Star Walk 6.0, Starmap, and SkySafari 3, show stars down to at least 50 times fainter than GoSkyWatch.