I have a tendency for the “old school.” Perhaps fuelled by powerful nostalgia but I often find myself favouring the way things were to the way they are now. Those same feelings apply to my passion for astronomy. My first scope, a 4.5” Newtonian on a shaky, undersized equatorial mount had manual slow motion controls and that was it. Even a sidereal-rate clock drive was beyond the meagre means of money earned from a Christmas job. Thoughts of computerised Go-To were to be found in my wildest dreams and at the time only available on a few scopes with price tags that would have taken years to save for. However, that meant I learnt how to navigate around the sky using star charts and the less and less used technique of star-hopping. It is a technique I still favour today with six of my seven telescopes currently mounted on manual Alt-Az mounts, with only the Celestron Nexstar 11 GPS benefitting from computer aided pointing and tracking.
My first star charts were contained in the venerable Norton’s Star Atlas, which provided this budding astronomer with enough detail to star hop to any object of interest that was within the range of the 4.5” Newtonian. However, as my skills improved, and apertures increased in size, the desire for more detail with higher limiting magnitudes saw a migration to Sky Atlas 2000 which plots stars to a magnitude of 8.5 and 2,700 deep sky objects. Despite using the even more detailed Uranometria 2000.0 at University, my personal preference remains Sky Atlas 2000, and for trips away, its little brother, the S&T Pocket Sky Atlas.
While star charts with varying degrees of accuracy and detail have existed for centuries, planetarium software has been available for only a few decades. Software that was once consigned to desktop computers and useful for planning a night’s observation, but perhaps less so in the field, can now, thanks to relentless march of technology, be delivered in ever more functional and user-friendly ways. This is readily apparent in the development of star chart apps for smart phones and tablets.
SkySafari by Simulation Curriculum is available in three versions with increasing levels of detail and functionality though my first experience was with the entry level SkySafari 3 Basic which I grabbed during a sale event on iOS for free. I found the app immediately accessible and intuitive to use, finding it particularly useful at outreach events to point out constellations, especially under London’s light polluted skies.
In the summer of 2014 I was preparing for a two week posting as the resident astronomer at the Sossusvlei Desert Lodge in Namibia when a 45th anniversary sale to mark the Apollo 11 moon landing was offered with 45% off each version. Such a discount was too hard to pass up, so I purchased SkySafari 4 Pro believing it would be an excellent teaching tool as well removing the need to carry any heavy star charts to Africa which would have eaten into my limited luggage allowance.
The entry level version which is targeted at beginners and those who might find their gaze occasionally drawn upwards includes approximately 119,000 stars (greater than an order of magnitude more than can be seen naked eye from the darkest site) as well as 220 of the best known deep sky objects as well as all the major planets and 500 asteroids, comets and satellites. It will accurately show the sky anywhere on the face of the Earth from 100 years in the past to 100 in the future. The Plus version takes things up a notch with 2.6 million stars and 31,000 DSOs as well as 18,000 solar system bodies including satellites. Pro gets very serious with over 27 million stars and over 740,000 DSOs as well as every solar system body discovered which total over 600,000 while displaying the sky with sub-arc second precision on Earth and beyond up to one million years in the past or future. The makers claim that the Pro version runs just as swiftly as the Basic, despite plotting vastly more objects. Having both versions installed on my iPhone 6 and iPad Mini 2, I have seen no difference in the performance level.
The user interface is cleanly presented and very intuitive to navigate with logical ordering of the top menu bar and sub functions. Many key options for visual presentation such as limiting magnitude are adjusted using a slider with a window showing the impact in real time of the change before returning to the main planetarium view. If you have used an app or navigated the internet on a touch screen device then using SkySafari will be second nature. Single finger taps and swipes, and dual finger actions to zoom in and out are the primary methods of control and the accuracy is very good as would be expected. Occasionally in a crowded star field I have found that the device believes I have selected a different object from what I intended, though is really a problem with my aim. Usually a second attempt will highlight the desired target.
The graphics are very attractive but crucially do not sacrifice the ability to easily extract the content required and navigate the sky. With multiple ways to represent the night sky including classical constellations, modern constellations, full colour and negative view, to name a few, you will find a display method which suits.
Each version of SkySafari comes with a number of graphical representations of real horizons (10 in the Pro version). While they look good, I feel these are a case of form over function as I find the artificial horizon can often hide parts of the sky I can actually see at my observing location. I prefer using a flat, opaque green horizon which only hides the parts of the sky not visible from your particular latitude. However, if you are handy with Photoshop you can create your own horizon and import which is function often seen in desktop planetarium programs and reinforces the idea that SkySafari Pro is not in any way cut price planetarium software.
For me, the real magic comes when you take the app outside under the stars. Hold up your touch screen device and the inbuilt GPS, compass and gyroscopes will correctly orientate the view to show you what you are looking at. It creates the impression you are holding a window to the sky which is able to annotate what you are seeing with your own eyes. The accuracy is very good with only occasional calibration requests which involve rotating your device through 360 degrees.
A useful addition is SkyWeek which is the mobile version of Sky and Telescope magazine’s “The Week’s Sky at a Glance” which provides daily listings of an interesting event such as occultations, eclipses and conjunctions. As well as the expected written description of the event ahead, SkySafari will plot the event in the planetarium sky view to show what you will see. This information does need to be downloaded and as such is the only function that requires an internet connection.
The Pro version benefits from almost 1,700 detailed object descriptions which include a tremendous amount of trivia as well as a stunning photograph of the DSO in question. Alongside that is all the basic stats, current coordinate data and brightness information which actually proves to be very useful for those of us who like to star-hop. By comparing the differential of altitude and azimuth coordinates of an easy to locate object such as a star, I can quickly offset to find the desired DSO. Having access to live alt-az coordinate data of every mapped object in the database is one of my favourite features and has made my nights of stargazing far more productive.
With several hundred thousand solar system objects contained in the Pro database, a quick zoom in on a gas giant will allow rapid identification of which moon is which in the eyepiece. That in itself is not that remarkable given the sub arc second plotting accuracy claimed, however I did come across a feature which quite honestly stunned me. On the morning of January 24th 2015 I woke early to observe a rare triple shadow transit on Jupiter. For once in the UK, the weather played ball with a time sensitive astronomical event. While waiting for my scope to acclimatise, I decided to quickly check the relative position of each Galilean moon. When I zoomed in to Jupiter not only was I presented with a high resolution image of the planet, but the three shadows were accurately plotted as well. This really demonstrates just how powerful a piece of planetarium software SkySafari actually is.
Barnard’s star in the constellation of Ophiuchus lies approximately six light years from the Earth and has the largest known proper motion of any star relative to the solar system at 10.3 arcseconds per year. Watching the proper motion play out in accelerated time using SkySafari is very impressive and another demonstration of the power of the app. Even more so, when you realise you can watch the relative movement from our closest celestial neighbour, Alpha Centauri or anywhere else that takes your fancy.
A favourite summer evening pastime of mine since childhood is to lie on a sun lounger in the garden and watch satellites pass overhead. At times my family would turn satellite spotting into a game to see who would spot the most. However, we would never know what was passing overhead. Was it a satellite or a piece of space junk? If it was a satellite, what kind? A spy satellite perhaps? With SkySafari there is no such ambiguity anymore. See a star like object drifting across the sky. Hold your iPad to the sky and match the green dot moving across the star chart to that of the one overhead. One click and you will know exactly what it is. For me this is one of the best outreach uses of the app and I used it numerous times to identify a satellite a guest had spotted at the observatory in Namibia. The accuracy of the satellite motion is remarkable, closely matching dedicated satellite tracking websites, even showing to the second when the satellite passes into the Earth’s shadow.
While it is not a feature I have tested, due to my current lack of a suitable mount (back to my affinity for retro with mostly manual Alt-Az mounts in my possession), SkySafari Plus and Pro versions allow for control of wide variety of computerised (both GoTo and Push-To) mounts via the wireless SkyFi or wired SkyWire accessory. I have read some promising reports of the performance online and hope to test this feature in the future when I acquire a suitable mount.
By this point in the review it is probably quite clear that I believe SkySafari is an excellent stargazing app. But are there any problems? One issue stands out and that is the question of light damaging your night vision. It can take 30 minutes or more to become fully dark adapted but it can be undone in seconds. While SkySafari does have a night vision mode which I always engage if using under the stars with brightness turned down (swipe up from the bottom of the screen to access the control centre and reduce the screen brightness), it does have a shortfall. Red light, despite what some amateur astronomers think is not a panacea for night vision preservation, it is just less damaging. As such, it is not ideal to leave the iPad on permanently, plus there are battery considerations as well. When reengaging the iPad, initially the user will be exposed to a non-red screen before the app opens back up. I am not sure if there is a high tech solution to this, but there is a low tech one. I have constructed a simple cardboard sleeve with a window of red acetate which I just slip onto the iPad before an observing session. The acetate does not impede screen sensitivity and protects against an inadvertent glance at a bright, colourful screen.
I might like the way things were, but this is one case where the evidence for the new demonstrates it to be leaps and bounds above the more traditional paper based star atlas. A clean, easy to navigate interface, attractive graphics and extremely powerful functionality make it a winner. As a tool for outreach, SkySafari is almost unparalleled in its utility and for those of us who take our astronomy rather seriously, it accurately plots more objects than one could possibly view in a lifetime. My only criticism as previously mentioned is the risk to night vision but this is easily remedied with a little bit of do-it-yourself ingenuity.
For more information about downloading this app for iOS or Android visit the SkySafari Astronomy website.