By Tony Hoffman

Pocket Universe: Virtual Sky Astronomy is an iPad app geared to newcomers to astronomy. It includes the usual planetarium view, showing the constellations in their proper positions relative to each other in the direction your iPad is pointing for any given time and location. It also features star and constellation quizzes, a solar system view that shows the planets in motion around the Sun, a section featuring individual 3D planets that you can spin, a section with astronomy news items, and more. The planetarium part of the app works okay, though it's rather basic, and some of the sections are amateurishly produced.

The app can be used in either Landscape or Portrait mode. After a brief, yet fun, animation (a fly-through of the solar system), the Home screenwhich changes color depending on the time of day you activate the appappears. The app's title appears at top center, and below it is an image of the Moon. Listed further down is the current date, the Julian date (a continuous count of days since the beginning of the Julian Period on January 1, 4713 BC, a measure frequently used by astronomers), the Star Date (in a nod to Star Trek, though there is no universally recognized conversion scheme between the TV series's Star Date chronology and actual time), and the lunar phase (Waxing Gibbous, when I tested the app). Below these bits of information, the rising and setting times of the Sun, Moon, and the planets that can be seen by the naked eye are listed.

Gaze into a Virtual Sky Appearing lower on the Home Screen are links marked Help, Virtual Sky and Extras, Planets, Orrery, What's Up?, and Ask. The heart of Pocket Universe, as it is with any planetarium program, is the Virtual Sky view, which lets you see the stars and constellations on your iPad's screen as they would actually appear in the night sky in whatever direction you point your device. It identifies constellations and bright stars both onscreen and via audio when they pass through the virtual crosshairs at the screen's center. Virtual Sky provides position and brightness data for the brightest stars, but no information on the vast majority of stars, which is unusual in a planetarium program.

The Extras section includes quizzes, depictions of the positions of Jupiter's and Saturn's brightest moons, 360-degree virtual views of the surfaces of the Moon and Mars, and more. While the latter items are good, the quizzes tended to be repetitive, asking some of the same questions over and over even when I got them right.

Tracking the Planets Clicking on What's Up? takes you to a table showing the altitude (in increments of 10 degrees) and azimuth (its compass direction, measured clockwise from due north) of the five planets you can see with the naked eye (Mercury, Venus, Mars, Jupiter, and Saturn), plus the Sun and Moon for a given location and date. At the bottom of the screen are right and left arrow buttons, plus a play/pause button, that let you view, speed up, pause, or reverse the motion of the planets over time.

The Help button takes you to a menu with five items. What's New shows you what has been changed in the current version of the app as opposed to the previous one. Getting Started teaches you some basics about the app. For instance, it tells you that the app can run on an iPhone, iPod, and iPad (I tested it on an iPad Air 2 ), provides a virtual sky view rendered for your location and time, and displays the 10,000 brightest stars, the location of the planets, Sun, and Moon, and the Messier catalogue of deep-sky objects.

The Planets section shows 3D rotating versions of the Sun, Moon, and our solar system's planets (Pluto is omitted), and includes basic data on each world. When you use the app in daytime, Earth is illuminated, but when you use it at night, our planet is in darkness, with just the faint outline of continents and the lights of cities. The globes vary greatly in quality; the Moon shows some detail on both its near side and far side, and Mars, Neptune, and Venus look fairly realistic (and Venus correctly rotating backwards). In contrast, the Sun appears as a glaring ball of mottled yellow and white, with sunspots looking like they were photoshopped in place, and Mercury appearing blotchy and nearly featureless. Forward and backward arrow buttons at the bottom of the screen take you from one planet to the next. Some basic detail is provided for each planet, including its rising and setting times in our sky, radius, distance from the Sun, period of rotation, orbital period, and number of satellites.

The Orrery view shows the solar system in motion, and can be tilted, squeezed, or pinched to change perspective. Through the use of front-arrow, back-arrow, and pause keys, you can freeze, speed up, or reverse the motion of the planets. The individual worlds are not identified in the Orrery view, although they're the same 3D planets that appear in the Planets section.

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Pocket Universe: Virtual Sky Astronomy (for iPad)