By Tony Hoffman

As the iOS version of a longstanding desktop astronomy software program, Redshift (for iPad) is one of the better apps of its kind that we've come across. It combines a planetarium view, which shows the stars and constellations as they really appear in the direction your iPad is pointing, with the ability to send you on three-dimensional virtual voyages across the solar system and beyond. Although it's priced higher than some iPad apps of similar quality, it's a worthwhile addition to any astronomy buff's repertoire.

Redshift is compatible with the Apple iPad, iPhone, and iPod touch. I tested it with an iPad Air 2, as the app seems ideally suited for a device with generous screen area.

The Night Sky at Your Fingertips By default, the app shows a virtual view of the night sky, even in daytime; as you turn the iPad, new constellations will slide into view. A horizontal line marks the horizon; as you pan downward, you see a representation of the grounda lake, sand, and grassbut the stars below the horizon still shine faintly through. To zoom, you can either spread two fingers apart while touching the screen, or double-tap the screen with one finger. By double-tapping several times, you can zoom through three levels of magnification. For a wide-field view, you pinch two fingers together or double-tap the screen with two fingers. In testing, the screen wasn't always responsive to the tapping gestures; I found that a light touch works best.

At the upper-left-hand corner of any screen you're on is a Home icon. Rather than the usual house, it's a globe with a pin stuck in it. It takes you to the default view of the night sky. At the upper right is a Search (magnifying glass) button. You can either enter the name of an object, or search for one from a drop-down menu classified by type (star, comet, asteroid, and dwarf planet, for example). At lower left, a Gear icon takes you to the Sky Settings menu, which lets you alter the view's appearance (such as how constellations are shown) and the type of data displayed. At lower right, a Tool icon lets you take 3D flights, return to the default sky view, and download new objects, such as comets.

When navigating in the sky view, if you tap on a star or other object, a red circle will pulse around it, and its name (or, in most cases, designationsuch as the star HIP 2927) will appear next to it, as well as at the top of the screen, where it also identifies the type of object. Tap a down arrow at the top of the screen next to its name, and a menu with a row of about five icons (depending on the type of object being viewed) appears below the name. The first icon, a lowercase "i," brings up basic information, such as the type of object, its magnitude, its position in both Earth-centered (altitude and azimuth) and celestial (right ascension and declination) coordinates, its position, and rising and setting times. The second icon is the Wikipedia W, which takes you to the object's Wikipedia page (if any). A faint, undistinguished star like HIP 2927, as well as the vast majority of the roughly 100,000 stars in the database, lacks a Wikipedia page, but the brighter stars, galaxies, and nebulas do. For example, tapping the star labeled Sadalsuud brings up the (rather detailed) Wikipedia page for its alternate designation, Beta Aquarii. The third icon, the image of a rocket, takes you on a virtual 3D journey to the object. Tapping on a new icon, a sphere with an object orbiting it, puts you in orbit around the object. An icon with a curved, two-headed arrow stops the object's motion.

Have Spaceship, Will Travel The 3D journeying function is Redshift's most distinctive feature, although we have seen similar features in some other astronomy apps, such as Star Chart (for iPad). By tapping the Take 3D-Flight entry in the Tools menu, you get a menu of flight targets: Sun; Moon; Earth; Planets and their Moons; Asteroids; Solar System View; Stars, Deep Sky; and Grand Tour. Planets and their Moons, Asteroids, Stars, and Deep Sky all have submenus that let you choose individual objects to journey to.

Each 3D voyage has two stages. First, the sky view pans until the target is in the center of the field of view. Then the camera zooms in on the object. The voyages vary in quality. The ones in our solar system (Sun, Moon, Planets, and Asteroids) are pleasing, as is the one open-star cluster, the Hyades, but stars and deep-sky objects are less impressive. The nebulas I tried to explore looked like fuzzy point clouds rather than celestial objects. The 3D voyages are best considered as an educational tool, as after watching them a few times, the novelty wears off.

Redshift is one of the better planetarium-type astronomy apps, with a detailed view of the night sky and a good range of objects to view. I didn't find its Search function as thorough as those of the Editors' Choice SkySafari 3, which offers more categories and individual objects to peruse. Redshift does add the 3D journeying function, which is a fun extra. The app is priced higher than SkySafari 3 and other similar programs we have looked at, without adding enough value to justify the extra cost. It's a very good app, but there are more economical choices that are just as good or better.

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Redshift (for iPad)