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Sky Guide: here's a great app for casual and experienced stargazers alike.

Sky Guide

by Fifth Star Labs

U.S. Price: $1.99, and $9.99 per year for

SUPERMASSIVE in-app subscription

Available from the Apple App Store 64-bit device recommended.

What We Like

Excellent graphics Ease of use

What We Don't Like

Only available for Apple devices Doesn't permit free rotation

THESE DAYS THE MARKET for smartphone planetarium apps is pretty crowded. Simply go on your Android or Apple app store, search for "planetarium," and you'll be presented with dozens of options, each with a dizzying array of looks and features. While many have specific uses for observers or imagers, it can be hard to find one that quickly shows you the sky without sorting through a lot of bells and whistles.

Sky Guide by Fifth Star Labs is a planetarium app for Apple devices (including an alert function for the Apple Watch) that sets itself apart from the crowd in a number of ways. Produced by photographer Nick Risinger and software developer Chris Laurel, the app features Risinger's seminal all-sky color Photopic Sky Survey (S&T: Feb. 2012, p. 70) as the base for the sky map. Like many other planetarium apps, Sky Guide will match the field of view when your device is held up to the sky, and it includes the Sun, Moon, and planets as well as the brighter moons of Jupiter, Saturn, and Mars (though none around Neptune and Uranus). But unlike other planetarium apps I've used, objects are represented by their appearance--or at least as a camera would see them in a moderately deep exposure--giving me a better appreciation for where objects really are in the sky in relation to other targets. The brightness of the stars and the background sky is adjustable by sliding two fingers up or down on the screen, allowing you to match the conditions at your location. This feature is very realistic and even imparts the familiar reddish-brown cast of urban light pollution along the horizon.

The app is unencumbered by a multitude of controls; there are only three tiny icons at the top of the screen. One brings you to a menu of options, another turns on or off the accelerometer that matches the view to the sky. The third at the top right is the search icon, which allows you to quickly find many objects, including those in the Messier and Caldwell catalogs, plus many other bright targets arranged by type.

Sky Guide has a nifty option that lets you change the appearance of the sky to different wavelengths in the electromagnetic spectrum based on other all-sky survey data. Holding your finger in one place for two seconds opens the filter window, which you use to reposition the pointer to select your desired wavelength filter. These include gamma ray, X-ray, ultraviolet, visible light (the default), hydrogen-alpha, infrared, microwave, and radio wavelengths. I found this feature particularly useful when hunting for astrophotography targets, especially nebulae.

Another feature within the app is its real-time tracking of 250 bright satellites. Sky Guide can send you a 5-minute advance alert when a particularly bright event, such as the appearance of the International Space Station or an Iridium flare, is about to occur. You can disable this setting in the menu, or set time periods when you'd prefer not to receive notifications.

Comets are another neat feature of Sky Guide. It looks like a lot of time went into presenting their appearance, and it was well worth the effort. Most bright comets visible at the time are displayed similar to their predicted photographic appearance, based on their solar position and our Earth-based viewing angle.

The depiction of the major planets incorporates the latest skins available from NASA and accurately shows their illumination. I was particularly impressed that the central meridian of Mars and Mercury both are properly displayed to match the local observation time, as are Great Red Spot transits on Jupiter. Several bright minor planets and the dwarf planets are also included.

Among the basic settings within the app, constellations can be represented as classic lines or as stylized "mythology" renderings. These tastefully appear only on the constellation at the center of the field, and fade away as you move on to a different part of the sky. You can disable the horizon to see the entire sky, though your view will still be "north up" no matter where you're pointing. You can show the ecliptic as a series of tiny Suns spanning the sky.

Subscription Content

A recent addition in Sky Guide is the subscription-based add-on of the "SUPERMASSIVE" feature ($9.99 per year). This increases the internal database; the entire NGC/IC catalogs are included, and the app's stellar database expands to more than 114 million stars. What's particularly captivating with the add-on is its high-definition feature.

The basic app lets you zoom in to an area of the sky to show the positions of some smaller objects, such as planetary nebulae, galaxies, and globular clusters. SUPERMASSIVE allows you to zoom into thousands of these objects in great detail, often incorporating Hubble and other high-resolution images (as well as the Moon). It's particularly fascinating to zoom into a galaxy such as M81 at high resolution and then search for M51, which cinematically zooms you out of M81 and into M51 to reveal tiny HII regions in this popular target. Occasionally, the limited number of galaxies in the SUPERMASSIVE database was noticeable; some galaxies in the Virgo Cluster surrounding M87 were notably absent even though they were labeled.

The SUPERMASSIVE add-on also includes an expanding collection of cinematic tours. My favorite is the depiction of several famous comet apparitions throughout the past three centuries, showing their swing through the inner solar system.

Sky Guide is billed as an app for astronomy enthusiasts of any level. And while I consider myself an advanced amateur who likes to image obscure targets, I often find myself opening this app rather than more-detailed planetarium programs. At $1.99 for the standard version, it's well worth the price.

S&T Equipment Editor SEAN WALKER has filled the memory of his iPad Mini with several planetarium apps.

Caption: The planetarium app Sky Guide for iOS devices incorporates several all-sky survey mosaics into the appearance, including coauthor Nick Risinger's own Photopic Sky Survey (left). Users can switch between several wavelength "skins," including infrared from the WISE survey (right).

Caption: Users of Sky Guide can zoom into an area of an object like M45 (far left), though with the "SUPERMASSIVE" add-on, you can continue to zoom in to reveal even smaller features and fainter stars (left).

Caption: Comets are rendered to show the position angle of a predicted tail based on the object's position from the Sun and Earth at the time of observation. You can speed up the time and track comets as they swing through the solar system.
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Title Annotation:Quick Look
Author:Walker, Sean
Publication:Sky & Telescope
Article Type:Product/service evaluation
Date:Aug 1, 2017
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