Three Sky Simulators for Astronomy Tested: Two Winners

Virtual sky/planetarium astronomy programs can display the sky from most any location and time. Uses include introducing novice amateur astronomers to the sky, learning constellations, planning an observing session, and controlling the movement of a telescope via the Mac's USB port. The three most popular products, all very mature in their development, are evaluated: Starry Night, TheSkyX and Voyager.

The International Year of Astronomy

The year 2009 is the International Year of Astronomy. From the website:

"The International Year of Astronomy 2009 is a global effort initiated by the International Astronomical Union (IAU) and UNESCO to help the citizens of the world rediscover their place in the Universe through the day- and night-time sky, and thereby engage a personal sense of wonder and discovery."

As a result, hopefully with the help of local amateur astronomy organizations and magazines like Astronomy and Sky and Telescope, people who want to find out more about their place in the universe will be buying telescopes (or dusting off old ones) and exploring the sky -- as we move into spring and summer weather here in the Northern Hemisphere.

Programs like those reviewed here are excellent at introducing newbies to the sky and are also used by amateur astronomers to plan their evening observing schedule. Knowing when constellations of interest rise and set and what's in them is essential for both types of users.

The programs reviewed here are: Starry Night Pro Plus by Imaginova, TheSkyX Serious Astronomer Edition by Bisque Software and Voyager by Carina Software

All are available for either Mac OS X or Windows, and there are various editions of each that span a range in capability and cost. I reviewed the Mac OS X versions.

The question, of course, is which one to buy? All have been around for a long time, each keeps getting better, but it doesn't make sense to own all three. Some plan of attack is required.

Review Methodology

There are several approaches one can take in reviewing these products. Each is tremendously complex: requiring a database of a million stars and coordinate transformations to show the user what the sky will look like at at any point in space, on the Earth, and at any time, past or future.

One can get lost in features and build a giant comparison chart. One can dig into coordinate transformations and quibble about the choices of algorithms for light bending on the horizon. In the end, however, it's all about the user experience. Which program will have terrific appeal, be fun and intuitive to use, which one has the best quality to price ratio, and which one will both easy for a beginner and usable in the long term by a serious amateur astronomer? It's my hope that in doing that, the reader will get a feel for the key ideas that lead to a purchase decision -- even if the developer dings me for not pointing out feature number 1,039,877.

To do that, I've built a comparison chart that summarizes exactly those key ideas that, in my experience, assist with the evaluation of this kind of software. Any other course ends up in deep geekdom and frustration.

I should point out that all of these programs are very good and differences are subtle. Yet there are differences that are derived from the philosophy and choices the developers have made. That said, I fully believe it's possible to take a different viewpoint and come up with different grades.

Here's the comparison chart. For the sake of brevity only, I have abbreviated each program name below: SNP, SKY, and VGR. Each numbered item in this summary table is discussed below.

Comp Chart

1. Going to Specified Date/Time

For the beginner or even a seasoned user, one of the first things to do is see what the sky will look like tonight. The ease with which one can jump around in time is important.

SNP: The date/time info is white on black (a default theme amongst several), technical in appearance, and has obvious popups for the time flow rate. The control for going forward and backward is fairly obvious. However, the granularity of the time increments could be finer. (B)

SNP time

SNP: minimal space and good looking

SKY: The control is oddly laid out. The icons for forward and stepping forward are hard to both read and interpret. The granularity of the time increments could be finer. (C)

SKY Time

SKY: messy icons, poor use of space

VGR: The control is compact and intuitive. The icons are easy to understand, the time increment popup is obvious and has lots of time options. Local time and UTC are shown together. (A)

VGR Time

VGR: Intuitive, perhaps old fashioned

2. Coherence of Customization

Astronomy software like this has a lot of opportunity for customization, perhaps too much. How the designer brings coherence to and separation of application preferences versus view options with menus, dialogs, check boxes, and popups is critical.

SNP: The options tab clearly lays out options for guides, local view, solar system, stars, constellations. However, application preferences have a mix of application operation and view options, namely brightness/contrast options and responsiveness, which can create confusion. (B)

SNP Prefs

SNP: App Preferences

SKY:Application preferences have check boxes to reveal or hide various Toolbars. For example, one must check the box for the display Toolbar to bring up buttons for sky guides. That doesn't seem appropriate for app prefs. The rest of the app preferences either have long lists which creates visual frustration or seem tangential to the function of the app. (C)

SKY Prefs

SKY: App preferences

VGR: The various sky grids, celestial, ecliptic, galactic are all controlled in one menu item: Display -> Coordinate grids. The associated colors are obvious and found in Display ->Colors or can be accessed immediately with a button. The app's preferences handle only application operations and general preferences for units: temperatures, time, angles, and metric units. This is a nice, clean separation of function. (A)

VGR Prefs

VGR: App preferences

3. Execution of Customization

After the developer partitions application preferences from view options, the question is then how the many options are executed to provide everything the user might want. All these programs provide essential features such as localization, definable horizon graphic, sky coordinate grids, constellation outlines, representation of Milky Way, red light night mode, stellar spectral type saturation, printing of a start chart, and so on. However, the presentation, choice of layout and design, drill down, and organization are important elements.

SNP: All of the available options for display are in the side tab, Options, which can be hidden to show more sky. Options are laid out in a way that suggests the scope of what one can do. Supplemental control is found in the Options and Label menus. However, the items next to disclosure triangles are also double-clickable, which brings up another sheet for options, typically color and brightness. It's awkward, but at least the options are kept together and an outline-prompt suggests clicking on the item itself. Showing the Milky Way in various wavelengths is something the other programs don't do. (B)

SNP Exec

SNP: Sky guides control

SKY: After one enables the right Toolbar, and they tend to popup in unpredictable places by default, then one goes to the Display Menu for finer control. Worse, for the customization of the sky coordinates, color and granularity, one must CTRL+Click a grid line, which is very non obvious. The corresponding dialog is irregular in layout. Also, the Toolbars take up a lot of room, although they can be rearranged. Newbies could be frustrated by the levels of complexity and visual geometry of options.

The Field of View Indicator is awkward to use and one of the defaults, binocular, insists on being 50 degrees angular extent when it should be 5 to 10 degrees. The Milky Way display is nice in the visible, but limited to visible light (or isophotes). The Milky Way longitude option is not explained in the manual. (B-)

SKY Exec

SKY: Sky guides somewhat irregular in layout

VGR: Voyager tends to be menu driven for options which is a good design choice because it keeps the display uncluttered. Every option for display control is contained within that menu which makes it easy for a new user to customize.

There is a logical grouping of detailed options in a single dialog and the linking of color options makes for an organized way to enable the myriad of different coordinate systems and labels that can be displayed. This makes the options highly discoverable and their location easy to remember. (A)

VGR Exec

VGR: All Sky guides nicely organized

4. Clarity, elegance of User Interface

There is a tradeoff between screen real estate, the size and design of numbers and controls and visible sky, independent of options to reveal or hide various functions. The look and feel can make users think they're on the bridge of the Enterprise, using a serious tool, or the app can feel a bit toy-like as a result of color and layout decisions. This can be a subjective judgment. All the programs use the method of click-drag to move the sky around and the mouse scroll wheel to zoom in.

SNP: This app has a low key, technical approach with a design that has a lot of information at the top and tabs on the left. When necessary, information is co-resident on the sky, but unobtrusive. The selections for font, colors, text sizes and menu layout are pleasing to this reviewer. When one wants to do something, the design tends to suggest how to achieve it. Field of view indicators are obvious -- they have their own tab, and a definable equipment list drives the size of the FOV circle. Alt/Az indicators, in text, are beautifully shown on the upper right along with a nice compass graphic. (A)


SNP Look and feel (Best use of space)

SKY: TheSkyX combines a dark night sky with a lot of gray-white space and lots of space between icons -- unless in full screen mode, and then some functionality is lost. It's almost as if the program were designed for younger users who might be put off by a compact and technical display. In that sense, the design aesthetics leave something to be desired by this reviewer. Also, little things tend to annoy because the program was written with a cross-platform tool, Qt. Dialog boxes are irregular, Right Ascension labels disappear when one scrolls down to the horizon, and dialogs don't always open (at first) to reveal full content. The Field of View and equipment manager isn't quite as intuitive as SNP. (C)


SKY: Look and feel (wasted space by default)

VGR: Voyager seems to fall in between the two other programs reviewed here. The design is generally clean and technical, but there are some idiosyncrasies. Two compass-like graphics display the azimuth and elevation, both graphically and numerically, of the screen center, take up some room and seem clunky compared to SNP's low key, low brightness blue text to accomplish the same with much more beauty. A toolbar of options is on the display by default, and it also looks clunky at first, but one can get used to it. It's almost like the plentiful icons in Microsoft Word for managing text. On the other hand, the time window and toolbar nicely disappear when Voyager isn't the frontmost app. That's nice. The FOV indicator requires telescope control turned on, and that's not quite as intuitive as SNP. (B)


VGR: Look and feel (good, but Alt/Az compasses not visible in screen shot)

5. Stability, launch times

All three programs launch fast (see chart) and none crashed on me over a period of weeks with the latest version I used. All were snappy on a MacBook Pro with NVIDIA 9600M GT graphics and 256 MB of VRAM. The user experience in launching, operating, and moving the sky around was virtually identical.

6. Installation, Mac integration

SNP: SNP uses a third party Java installer that's kind of dumb about ejecting the first disc and user instruction to load the second disc. Also, I got an alarming message about the Java version I am using that turned out not to be a problem. All this needs to be turned into a more Mac-like experience. It dragged the rating down. The development system is Xcode and the app is mainly Carbon with an increasing number of Cocoa APIs. The code is mostly C++ with some Objective-C. The use of a native Mac development system creates a visual sense of quality. (B)

SNP Java

SNP: Java installer needs work

SKY: TheSkyX installed nicely, and there were no problems.The leap from Windows C++ Foundation Classes to Qt and C++ has been laudable, but results in slight irregularities in cosmetics and detracts from the sense of quality. (B)

VGR: Voyager also installed without a hitch. The Mac version was developed with Xcode 3.1, C++ and Carbon. The use of a native Mac development system creates a visual sense of quality. (A)

7. Documentation

SNP comes with superior paper documentation. It includes:

  • Starry Night User's guide with eight page index, 208 pp.
  • Starry Night Companion, with index, 192 pp.
  • Starry Night Quick Start, a six panel, book-size, fold-out

In an age when large companies just can't be bothered to produce an elegant paper manual, Imaginova has held the course for years with this tradition. This isn't an issue of being Green; rather, these programs are complex and use up the entire screen, leaving no room for a PDF manual -- unless one uses Leopard's Spaces. That's still awkward, and a paper manual is most welcome. SNP is produced in Canada, and the English uses U.K. spelling, not U.S., but that's a nit. (A+)

Both SKY and VGR come with PDF manual embedded in the application package and available from the Help menu. TheSkyX's PDF User Guide is 239 pages and has a three page index. That's barely adequate, so the score is reduced. Voyager's PDF manual, also in the Help Menu, is 165 pages and has a six page index. Both of these PDF manuals are full of screen shots, but I give extra consideration to Voyager for a better index, a seeming lost art.

The boxed version of VGR comes with a printed manual (A), but the boxed version of TheSkyX does not. (B)

8. Telescope Support

All three programs will connect to a telescope that has support for external control software. Unfortunately except for the Vixen SX telescope mounts which (commendably) uses Ethernet, the major manufacturers are still using the ancient RS-232 serial interface. That's solved by using a USB to RS-232 interface cable, and users have the best success with Keyspan brand cables. Carina Software sells Keyspan cables for specified mounts.

SNP: Starry Night supports a healthy range of devices. A screen shot of the configuration options is below. (A)

SNP Telescopes

SNP: Telescopes Supported

SKY: Supports Astro-Physics GTO mounts, all major Celestron NexStar mounts, iOptron SmartStar mounts, Takahashi Temma mounts, Vixen SX, and Meade Autostar mounts. The manual has very detailed instructions on how to get set up with each kind of mount. (B+)

VGR: Supports a long list of telescope mounts, including Astro-Physics GTO, Celestron NexStar, Losmandy, Takahashi, Meade Autostar and more. The complete list is on Carina's Website. The manual doesn't go into much detail as TheSkyX, but the connection dialog is excellent. (A)

Final Focus

There is probably no such thing as a universally objective assessment of these very complex programs. I have, for reasons of space, time and sanity, left out huge chunks of details that each developer will feel could have swung the tide in their company's favor. In the end, all one can do is be as dispassionate as possible and try to home in on some important aspects of the software that will help with a purchase decision rather than technical minutiae.

I have been using all these programs for all of the time they've been available on a Mac, and if I could only use one, it would be Starry Night. Voyager is a close second for me, and while the comparison chart doesn't strictly reinforce that decision, the numbers are close for those two, and the ratings confirm that SNP and VGR belong in the top two spots.

Because of its simplicity (in a good sense), clarity, and focus, I would recommend Voyager for those with less experience in amateur astronomy. However, for seasoned amateur astronomers, Starry Night Pro seems a better choice because it trades some simplicity for power. But barely. Voyager enthusiasts may, with justification, quibble.

TheSkyX is a laudable effort and will find an audience, but as hard as I tried, I couldn't find any area where it was demonstrably better than the other two products.

It's important to go to the vendor's website and determine the various features offered in each version. For example, Starry Night ranges from U$79.95 for Starry Night Enthusiast to $149.95 for Starry Night Pro and $249.95 for Starry Night Pro Plus. Upgrade information from one to the next is on the website.

TheSkyX ranges from the Student Edition ($99) to the Serious Astronomer Edition ($129) to a Professional Edition for $279. No information about upgrade paths was available at the time of this writing.

Similarly, Carina Software has SkyGazer for true beginners priced at US$49.95 and Voyager for more experienced users: $99.95 for on-line download only, $149.95 for CD with printed manual, and $199.95 for DVD with prinred manual and additional star and galaxy catalogs. There is an upgrade path for SkyGazer purchasers.

In general, the high end software will have features of interest to advanced amateurs, and an absolute beginner would do well with Starry Night Enthusiast or Voyager on-line edition.

My recommendation is to use this review to home in on the product of choice, then figure out which level meets your needs and budget. For example, telescope support may be an issue that steers you to one of the products.

Amateur astronomy is an amazing endeavor. With the right kind of equipment, amateurs have been able to make real contributions to science. Most good sized towns have a local amateur astronomy group, but even if yours doesn't, the Internet creates a wonderful virtual community.


  1. Astronomy Web Guide
  2. Local Astronomy Clubs
  3. telescope and binocular products and buying advice

Products Reviewed:

Starry Night Pro Plus (6.2.3)
$249.95* (boxed version)
Mac Req: Mac OS X 10.3.9, G4 800 MHz or better 
TheSkyX Serious Astronomer Edition (10.0.2)
(Note: a new version is imminent, but wasn't available in time for this review.)
$129.00 (boxed version)
Mac Req: Mac OS X 10.4.8, 2 GHz Intel Core Duo or 1.25 GHz PPC
Voyager (4.5.3)
$99.95 (online version)
Mac Req: Mac OS X 10.3, G4 or Intel, 1 GHz 
* Starry Night Pro ($149.95) is roughly equivalent to the other products reviewed. 

About the author: John Martellaro holds a B.S. in Astrophysics, an M.S. in Physics and has done Ph.D. work in Astrophysics. In his career, he has been a U.S.A.F. officer in the Spacetrack Network, worked for NASA and Lockheed Martin Astronautics. John has been a life-long amateur astronomer. Like many amateurs, he uses a 20 cm Schmidt-Cassegrain telescope.