Star Chart is a universal app for iOS that charts the sky for any date from the ancient past well into the future. It’s a beautiful app, always being improved, a great introduction to the night sky, but suffers from a few astronomical errors and has limited settings.
The most important thing to know about a star chart app like this is that it can help one identify what’s seen in the night or even day time sky. (Or fantasize what’s behind all the pollution.) Casual observers may be out on a starry night, camping, wondering what a bright light is. Or an amateur astronomer may wish to identify an forgotten, seldom seen constellation. Or perhaps one would like to know when Mars will rise or set on a particular night, in the context of the rest of the sky. This app, priced at only US$2.99 will do that nicely.
Fig #1, Western Sky, about 9 PM local
One of the major features of this app, like some others, is the ability to exploit the compass in the iPhone or iPad and slave the view to the actual sky. You can hold, say, an iPad up to the sky, and it will be like looking through a chunk of clear glass. The iPad shows you what you’d see if the iPad weren’t already displaying the view.
The developer pointed out the key features.
- Star Chart is under 20 MB — so that you can download it when out and about looking at stars.
- Star Chart is a universal app. We charge one price for the app on both iPhone & iPad. No extra charges for HD tablets. [Currently, however, there is no explicit support for the iPad 3 Retina display.]
- Star Chart includes 3D planets in our star gazing app — we don’t sell another app for “flying to” planets. You can visit any of the planets and their moons all within Star Chart.
- Our team is made up of console game developers. We’ve all made AAA console games for companies like EA in the past — so we focus very much on not just the accurate data and positions, but also on striking visuals. Our app is widely considered the most beautiful of the star map apps.
- We are committed to constantly updating Star Chart (for free) to ensure that Star Chart is always improving. However, we don’t just add every feature possible, we are very targeted and choose to add features as they make sense for our app and consumers. We believe Star Chart should be beautiful, slick and clean.
- Our constellations images are all digitally enhanced versions of Johannes Hevelius’ original engraved constellation artwork from his seventeenth century star atlas Firmamentum Sobiescianum.
- We include over 115,000 stars in our catalogue on all iOS devices. [Up to magnitude 10.]
- We accurately represent the directional flows of Jupiter’s gas cloud bands. When viewing Jupiter you’ll see that the gas bands move in opposite directions and the swirl of the Big Red Spot are all accurately represented.
Star Chart has a modest number of settings. That can be good or bad, depending on the user. For example, a beginner or casual user may not want to be distracted by astronomical terms that are unknown or not useful. On the other hand, an experienced amateur might be annoyed that there’s no switch to turn on the galactic plane or even the ecliptic. This app is designed for fun and education, not strictly technical astronomy.
Fig #2, Main Settings
Note that Augmented Reality (AR) mode must be in the off position to be slaved to the current sky. The sense of this nomenclature seems a bit confusing. Anyway, when I enabled it, I saw a distinct jitter, maybe a few degrees, that wasn’t there in another, similar app I compared to, as I moved about the sky. I did that to make sure each app was accessing the compass correctly. (An iPhone 3GS, 4 series, or iPad is required for this mode because they have a compass.) I sent a video of the jitter to the developer, but have yet to hear from them.
Fig #3, Display Settings are minimalist
You can look at the sky at any time from thousands of years into the past or future, from any point on earth. One of the things I really liked is the slider on the right side for selecting the year, month, time, etc.
The Star Settings will allow you to set the magnitude limit, from 6th (5,017 stars on the sphere) to 10th (116,567). Note that 6th magnitude is about the faintest star one can generally see, with some exceptions, and that a half sphere equates to 2508 stars. You really can count all the stars in the sky in an hour.
You can turn on atmospheric effects, a slight amount of scattering of the light or look at the sky as if there were no atmosphere at all. This is a nice option, especially for those who may be experiencing astronomical nirvana in Chile or Arizona and New Mexico in the southwestern US.
Fig #4, Atmospheric effects off, compared to Fig #1 above.
Even though this app is an inexpensive tool intended to educate and inspire, it also gets held to a higher standard. That is, experienced amateurs, and perhaps even professionals, may end up using it, and a certain amount of trust is expected from astronomical software because, after all, it represents reality. I noted several small errors plus a complaint.
The first, somewhat serious, is displayed when looking to the west in the current night time sky. In Star Chart, the most central part of the Milky Way goes dashing right through the middle of Orion. (Figs #1 and 4). I checked with another app, The Sky for the Mac (Software Bisque) as well as some other apps, and they all show the brightest part of the Milky Way going north of Orion but mostly south Gemini.
Fig #5, Milky Way, from The Sky, for OS X
The second error I found, or so it appears, is the relative size of Saturn compared to its rings, which I saw when I zoomed in. Here’s a comparison with an actual photo of Saturn at almost the identical aspect angle.
Fig #6, Saturn in Star Chart and compared to actual photo, NASA, GSFC
The third error is more forgivable. The position and appearance of the earth’s moon in Star Chart is based on its position, but not on the dynamics of the solar system as a result if a bug in this version. As a result, eclipses are not calculated correctly and depicted. That would be even more forgivable, except that the developer touts the 3D details of the planets as one zooms in. As I said, this is complicated stuff, and the app doesn’t lay claim to such accuracy in the dynamics. It’s just something to be aware of.
Here are the screen shots from the lunar eclipse of 10 December 2011, both shown at 0509 AM MST. The eclipse is partial at this stage, just before the moon sets. On the right, SkySafari gets it right.
Fig #7, Star Chart (left), SkySafari (right), 0509 MST, Eclipse of 10 Dec 2011
One thing that Star Chart does a very good job of is depicting the relative phase of the moon in real time at very coarse resolutions. You’ll have no doubt about what the phase of the moon is without having to zoom in very far.
The final issue isn’t really a problem, just a complaint. I noted that even after the sun has set, the visual effect of a lens flare is introduced. This makes for faux-realism (when the sun is up), but a distraction like that really doesn’t have a place in an app like this, in my opinion, especially after the sun has set.
Fig #8, Lens flare, after sunset
Star Chart requires iOS 3.0 oer later and is compatible with iPhone, iPod touch and iPad. (iPhone 3GS or later, iPad with compass for Augmented Reality mode). It has been localized to English, French, German, Spanish, Italian, Chinese, Japanese and Korean.
This app makes its claim to being beautiful in its effects — and it certainly is. I should note that the astronomical calculations to display the sky from any position on earth and time aren’t trivial, and the developers should be pleased with the overall result. However, apps like this demand special and great attention to detail, beyond even what super competent developers are accustomed to. That expertise usually comes from an astronomy background (or extensive consulation) in order to extract that last bit of accuracy.
Because of the sky jitter, the limited settings, and the minor astronomy errors, this version can’t really receive a “solid” rating at this time. But that shouldn’t keep you from exploring it on an informal basis and having a lot of fun. There is awe and inspiration to be had here. (Updates are coming and free. See below.) If you’re really into astronomy, there are competing apps, like Star Walk and SkySafari, equally priced, that have strong reputations, that you may also want also want to explore and compare to. After, all, a $3 price tag invites that kind of exploration.
The Developer Responds
There was a bit of an email snaufu on the developer’s side, but I now have their response.
“The comment on the eclipse is something we’ve very much aware of and have recently uploaded a fix for (waiting for Apple’s approval). There was some last minute bug in our code before the latest update that ruined the eclipses (they were working before). The up-coming update will fix this and add a few more features on eclipses and transits.” Here’s a screen shot of a Venus transit for 2012.
“We have also added the plane of the ecliptic in this last update, so again a shame we got there a few days after your review. Retina Display is also on our list of new additions to this latest update — so all devices that support retina display now have increased icon sizes and more. This has taken a while to get to as we’re very intent on keeping the file size low while improving the content.”
Regariding what I called jitter: “We’re aware of this jiggle as shown, and we regularly spend time adjusting the augmented reality code in Star Chart. What we have found is that it is possible to remove the jiggle when stationary, at the cost of a more ‘digital’ experience when moving — i.e., the screen would hop between locations more as you held it in your hand and small movements occurred. We have chosen to favour the practical use case of a consumer holding the device in their slightly unstable hand than make it work great when e.g. placed face up on a stationary table.
Having said that, we continue to work towards solving both smoothing of the jiggle when stationary, while also allowing for a responsive panning scenario. A future update will hopefully solve this.”
With these fixes, attention to the Milky Way and Saturn, and the developer’s commitment to constant improvements, I’m confident the next version will earn a higher rating.