When I reviewed Luminos - Astronomy Companion last year, I gave this iPad app an Editors' Choice for educational astronomy apps thanks to its usefulness to a range of users, from beginning stargazers to advanced amateur astronomers. Now in Version 9, it has added new features, most notably three versions of the UCAC4 star catalog. These are downloadable from within the app and can let users discern much fainter stars than they could with previous iterations of the app. The app has also added support for iOS 9 and the Apple Watch. At $14.99, it now costs $5 more than when I first reviewed it at, but the additions to this Editors' Choice app are well worth the extra cost for serious amateur astronomers.
Astronomy iPad apps tend to be geared either to novice stargazers or experienced amateur astronomers, while a few of them, such as the Editors' Choice SkySafari 5 Plus , do a great job in bridging both categories. Luminos also is likewise useful for a range of users, though its features are generally geared a bit more toward serious amateur astronomers. For them, it's a magnificent tool, depicting more stars, comets, and asteroids than any similarly priced astronomy app I've seen, as well as offering advanced features like the ability to control a telescope.
Luminos is also compatible with the iPhone, and the iPod touch, and the app's current version requires iOS 9 to run. I tested it using an Apple iPad Air 2 running iOS 9.3.
Design and Features
Luminos has a typical interface for a planetarium program, with most of the iPad's screen used to show a virtual view of the sky. The screen will show representation of the night sky in the direction you're holding your iPad. It's easy to move around in Luminos. You can pan horizontally or vertically by swiping the screen with one finger, zoom in by pinching the screen with two fingers, and zoom out by stretching two fingers. A line near the bottom of the screen marks the horizon. Unlike with some apps, such as Redshift (for iPad), Luminos doesn't normally show stars that are below the horizon. However, you can see objects below the horizon by searching on them, and then zooming in. During the daytime, the sky is shown as blue, but the stars are still visible.
The Search icon, a magnifying glass, is at the screen's lower left. Touching it opens a menu titled Browser, whose first item, View from Space, transports you on a journey outside our solar system, letting you look back and see all the planets in their orbits. To return to Earth, you press the Home icon in the upper-left portion of the screen.
Below View from Space are five categories of objects to search on: Solar System (the Sun, planets, and moons); Stars (catalogs and constellations); Satellites (satellites and orbiting craft); Small Bodies (comets and asteroids); and Deep Space (galaxies, nebulae, and clusters). Touching Solar System brings up entries for the Sun, Moon, and planets, as well as Mars' moons, Phobos and Deimos. Pluto is classified as a dwarf planet, as are Ceres, Eris, Makemake, and Haumea. By tapping on Earth, you can access a list of solar and lunar eclipses, and examine their circumstances by tapping on a particular eclipse.
Touching the name of any object centers it on screen, and the name of the object appears at the bottom of the screen, along with a row of icons, which vary slightly depending on what object is in view. A Crosshairs icon centers the object, a magnifier zooms in on it, and an icon showing a scroll adds it to a list of objects that you can create and name (by typing in a name using your iPad's virtual keyboard). Touching an icon showing a person pointing to the sky adds it to a list of objects you've seen. An icon showing an object orbiting a larger object gives you a close-up view of the planet, and an icon showing a label lets you toggle labels of the planets features on and off. An Information icon lets you see brightness and position data for each object.
An Astronomical Number of Stars and Asteroids
Under Stars, you can choose from lists of Named Stars, Brightest Stars, Nearest Stars, and Constellations. Objects that are grayed out are below the horizon, but are still accessible. By default, Luminos shows the 118,000 stars in the Hipparcos star catalog. You can also download any of four additional catalogs free of charge just by pressing a button. They include Tycho 2, with 2.6 million stars, plus 3 versions of the UCAC4 catalogue: light (with 26 million stars), medium (with 56 million stars), and complete (with 114 million stars). You can download multiple catalogs and switch among them, too.
Be aware, however, that the larger the catalog, the more disk space it consumes. While Tycho 2 takes up 106MB, the light, medium, and complete versions of UCAC4 take up 1.1GB, 2.2GB, and 4.6GB, respectively. While naked-eye observers can make do with the Hipparcos catalogue, anyone who looks at the night sky with binoculars or a telescope will want to download at least Tycho 2, which shows stars as faint as magnitude 11.5, about the limit of what you can see with a small scope in a light-polluted suburban sky. The UCAC4 catalogs go much deeper, with the complete version showing stars fainter than magnitude 18, which is about a millionth of the brightness of the faintest star that can be seen with the naked eye.
The Satellite section lets you search for artificial satellites by name. Space stations and the 100 or so brightest satellites are shown crossing the sky in Luminos, but you can hide them by unchecking a box. With Small Bodies, you can render more than 37,000 comets and asteroids, which is more than SkySafari Plus 5, or any sub-$20 program we've encountered. (The $39.99 SkySafari Pro 5 can render every comet and asteroid ever discovered.) Under Comets, you can find an individual comet from a list or search for it by name, and reveal or conceal the whole lot of them by checking or unchecking a box. You can do the same for a number of types of asteroids (such as Main Belt, Apollo, and Jupiter Trojan).
The Final Frontier
The Deep Space section lets you search on galaxies, nebulae, and star clusters from the main catalogs of such objects, such as Messier, Caldwell, NGC, Herschel, and Barnard. From the Browser menu, you can also access a list of objects you have marked as seen. Observation Lists includes your own custom lists, plus the Messier, Caldwell, and Herschel deep-sky catalogues. A Location tab lets you set your location for anywhere on Earth, and a Settings tab lets you change a wealth of settings related to the appearance of the sky and what data is shown.
Additional icons across the bottom of the screen include Time, Date, Telescope, Elevation, and Angle. With Time, you can speed the sky up to watch the motion of the stars and other objects, reverse the motion, stop, or return it to the present date and time. Date can show you the current phase of the Moon on that date, as well as show you what objects are visible at what times, for the present date. Tapping the Telescope icon will show you the field of view for different telescope, eyepiece, and camera combinations, and let you configure the settings and wireless connection so you can control a telescope from the iPad. Elevation has a slider that lets you zoom out to see the Earth from space. The angle lets you set the field of view. The choices are 60 degrees, 10 degrees, 1 degree, 10 minutes of arc (1/6 of a degree), and 1 minute of arc (1/60 degree).
Light Your Way
There are several improvements to the app since I last looked at it. In wide-field views, galaxies and other deep-sky objects are depicted generically. For instance, a galaxy shows as an oval with an S shape drawn through it, to represent spiral arms, though to me it resembles the Yin/Yang symbol. Zooming in will add an image of the galaxy within the oval, which wasn't the case when we originally reviewed Luminos. The presentation of planets, which grow into disks if you zoom in enough, has also been improved. The downside to the additions to Luminos in Version 9 is the large size of the new star databases. If you want to the app to render very faint stars, you take a major hit in disk space, which can be a precious commodity on an iPad. Before downloading one of the new catalogues, you'll want to ask yourself how many stars you really need.
Luminos is one of those rare iPad astronomy apps that manages to bridge a range of experience levels, from stargazing newbies to advanced amateurs. In that respect, it is similar to our other Editors' Choice astronomy app, SkySafari 5 Plus. While SkySafari is slightly better at showing beginners around the night sky, offering both more data and (in many cases) descriptions and/or large images of the objects it shows, Luminos—with its larger databases of astronomical objects— is somewhat better for astronomy enthusiasts. Amateur astronomers of all levels are lucky to have two such capable apps to choose from.