With spring upon us and the constellation Orion hanging gloriously in the western sky at sunset, it’s a great time to explore the night sky with a telescope or binoculars and a personal guide to the sky on your iPad. SkySafari 3 is a dynamic star chart that will help you identify stars, planets, nebulae and more. It’s the best of all the star chart apps for iOS. Treat yourself or bestow it on a youngster.
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For years and years, astronomers had (bound or loose) paper star charts. They were a labor of love, but very hard to use — and static. With the advent of the personal computer, it became possible to do a lot more, especially for amateur astronomers who would use popular sky chart software like Starry Night and Voyager to plan the night’s observing program. That would typically entail printing selected portions of the night sky on paper and taking them to the telescope.
The iPad changes all that. You can sit with the telescope or binoculars, iPad in hand, and then SkySafari will even go into “night vision mode” so that the display won’t destroy the dark adaption of your eyes. The iPad is perfectly designed for this kind of use.
Western Sky from Denver, CO, early evening
Even if you’re not a serious amateur astronomer, this app has a lot to offer. You can identify planets and satellites, learn the constellations, and, in fact, take a short course in astronomy, so good is the supporting material.
Features
Before I get into the meat of the review, let’s take a look at some of the key differentiators supplied by the developer.
- Accuracy. Sky Safari accurately displays eclipses of the moon and sun and transits of the inner planets. When the Gallean moons transit Jupiter’s disk, if a shadow is visible, it will be displayed, and light travel time is taken into account for eclipses. Our planets, moons, stars and deep sky objects are drawn realistically and correctly to scale, unlike most other apps.
- Depth. Our basic version has a database of 46,000+ stars to 8th magnitude. That makes it small enough (50 MB) to download without Wi-Fi. Almost all the other apps have only naked-eye stars (about 10,000). Our basic app is actually useful for deep sky object hunting with binoculars or a very small telescope
- Content. SkySafari has extensive material about starts and planets. We have much more information, professionally written. Most other apps just give you Wikipedia links, which you can’t even use in the field without an Internet connection.
- Customization. Many more options for controlling the appearance of the sky charts.
- Satellites. A database of 150+ satellites, displayed by name, in the basic version.
- Retina Display support in iPad 3.
- User definable terrestrial horizon.
- With iPad VGA or HDMI adapter, SkySafari can send the display to a big screen TV.
— not true of others which have only naked eye stars.
Versions and Requirements
SkySafari 3.2 comes in three iOS versions. This review is of the basic version for US$2.99. More advanced users have additional options: SkySafari 3 Plus ($14.99) extends the star database to 2.64 million (to magnitude 12), 31,000+ deep sky objects, 4,100 asteroids and includes telescope control. SkySafari 3 Pro ($59.99) in addition to telescope control “includes over 15.4 million stars (to magnitude 18) from the Hubble Guide Star catalog, plus 742,000 galaxies down to 18th magnitude, and over 583,000 solar system objects — including every comet and asteroid ever discovered,” according to the developer. Version 3.2 has been released for basic and “Plus.” The Pro version is awaiting approval and is still at 3.1.1. Southern Stars has a table that compares the three apps, their features, and details the object counts.
Each app is a universal binary and will work nicely on the iPod touch and iPhone, but the app really shines on the iPad with a Retina display. The iPad version requires iOS 4.0 or later. The app is available only in English.
Settings
One of the nice things about the SkySafari series is the extensive customization of the display. Even the basic version has more customization than, say, Star Chart, previously reviewed.
Here are just a few examples:
Appearance Settings
Consellation Options
I should note that the basic version omits equatorial, ecliptic and galactic coordinates as well as the corresponding equators and poles. That’s appropriate because the basic version is for beginners who may not yet be familiar with these concepts. They’ll be more focused on the visual experience.
Documentation
Here is where this app also stands out. The Help section not only describes the app in detail with a basic Introduction and detailed explanations of the menu bar and settings, but also includes two fabulous additional sections: Basic Concepts and astronomy Links. The Basic Concepts section, written by the author, is in effect a short course in astronomy. You’ll learn the basics of stellar magnitudes, parallax, precession, eclipses, astronomical calendaring and time, the types of stars and a lot more.
Major, detailed Help, Basic Concepts (a virtual astronomy class) and important links.
Basic Concepts: Eclipses (with terrific diagrams)
There are apps that are intended to inspire and can often go beyond the reader technically if they’re beginners in astronomy — like Wonders of The Universe. Other apps do astronomical calculations, like Wolfram Astronomy Course Assistant, without really teaching the fundamentals first. SkySafari’s exposition, on the other hand, will actually teach you the fundamentals of astronomy. Never has so much accurate and technical science knowledge been included in a $3 app.
The links will take you directly to a very thoughtful list of the best astronomy websites. This set of Help, Basic Concepts and links is the best set of documentation ever in a technical app for iOS.
Using SkySafari
All you need to do is launch SkySafari, and it will look up your location. It’s important to let it do that, with justifiable confidence, so that it can display the sky correctly for your location on earth. The Menu bar has all the functions you’ll need to change the date and time, search for an object, and customize with Settings. In fact, one of the settings is to make the Menu bar go away in landscape mode, but access it via portrait mode. That’s an elegant way to handle both access to Settings and create a clean display in the most likely orientation: landscape.
Pick a default horizon (3) or roll your own.
If your (i)device has a compass, the compass mode will allow you to hold the iPad up and see the sky exactly as if you were looking through a chunk of clear glass. The iPad shows you what you’d see, day or night, if the iPad weren’t already displaying the view. For devices without a compass, like the iPod touch, or if you want a slight smoother, more accurate view, you can use the Gyro mode. But that mode requires some pointing and set up. The Compass mode is immediate. You can use one or the other but not both.
The display of the night (or daytime) sky is awesome. If you want to see the sky as if there were no sun, you can set that option in the Horizon & Sky Settings.
Another nice touch, under the Milky Way Setting is the ability, with a slider, to set the visible intensity of the Milky Way. That’s not just for show; it may be desirable to either help you locate it or, alternatively, suppress it if you’re trying to focus on something nearby.
Information display, the star Betelgeuse in Orion. A virtual encyclopedia.
If you select a constellation or planet or star, the Info item in the Menu Bar will display an extensive amount of information on that object, and some of it is dynamic, like rise and set times. Then press the “Center” button to home in on the object, independent of whether it’s currently visible in the sky. The information displayed about each object is accurate and professional, and I found no errors. That’s because the author is technically experienced in astronomy and isn’t just copying information, without experience and insight, from a data source.
If you pinch zoom, you can actually see the details of planetary surfaces. For example, the developer mentioned that, “We use the Cassini map of Jupiter. The program adjusts the longitude of Jupiter’s central meridian automatically (internally) to give you accurate transit times for the Great Red Spot.” I zoomed in on Jupiter and let the clock run to see the movement of its satellites. It didn’t take long before I saw a transit, and quite pleasingly, here was the shadow of Io on Jupiter’s disk. This is an amazingly accurate and complete app in its solar system dynamics.
Jupiter – Transit of the moon Io (white disk). Note the dark, circular shadow on Jupiter’s surface, below and left.
The database of satellites, 150 or so, in the basic version is updated dynamically and transparently without a need for a version update.
A Technical Aside
Some users may note that one has to zoom in fairly far to see the phases of Mercury, Venus and the moon. At a normal sky view, say 70 x 50 degrees, these bodies are shown as a fully illuminated disk.
The Star Chart app showed that there is some additional latitude here to introduce the visible phase at a coarser zoom setting, and I hope the SkySafari author will consider that option. After all, it’s a bit odd to see the lunar crescent in the actual night sky and then see SkySafari’s fully illuminated disk if not zoomed in sufficiently. That cross-over point is a matter of discretion, so I consider this a a minor issue because the software is actually trying to depict the object brightness, like stars, via the size of the disk until you zoom in closer.
Conclusion
This app represents an enormous undertaking. The celestial mechanics, proper use of data sources, mathematics and documentation are extraordinarily demanding in astronomy apps. This kind of app can’t be thrown together by an ordinary developer, and the harsh eyes of professional astronomers, professors and the entire weight of the history of astronomy can come crashing down on the slightest bit of unprofessionalism or carelessness. This app measures up in every way, and even exceeds my highest expectations based on my own career in the field. Considering that it’s priced at $3 makes it even more amazing (and valuable).
Because of the careful attention to detail, the error free execution (so far as I could test), the detailed dynamics, the fabulous documentation and the breathtaking visual implementation, this app earns a rare 5/5 rating.