On the Watch

Starmap on the Watch? Really ?
What would be useful for sky lovers on the Watch? This was actually a quite difficult question to answer. New device, new usage ... new needs. This watch is about making our lives easier, reaching the needed information as quickly as possible, in the flick of a wrist.

Watches are used to answer simple questions like What time is it? Starmap on the Watch keeps it as simple as: What can I observe tonight? and  What is that bright object in the sky?

In the first version of Starmap on the Watch, I was displaying – very nicely – all planet positions in real time, with right ascensions, speeds, phases and event times. But when using it for real... I felt this was actually useless. Some users did like it ... one wrote me it looked like an old Casio display ... but was it really useful? Obviously not. The Watch is not a mini-iPhone on your wrist. It is a secondary screen, always at hand, quickly providing the information you need:  When is my next meeting?   How far am I from the bus stop? and  When is the sky really darkest tonight?  ... a very important question for astronomers!

For Everyone
The free version of Starmap is available for the Watch. More specialized features will certainly appear in the future, and all your requests are welcome.
After installing the App, you have to grant access to your location (Figure 5) if not already done. The authorization is given only once, on your iPhone. If you have used Starmap 2 before, and granted access before, the Watch will not ask you. Also, if your position changes by more than three kilometers, Starmap will automatically recompute a new ephemeris.
When you launch the App during the day, that night's events appear in chronological order, from sunset to sunrise. After sunset, the App will tell you where planets can be seen in the sky...or when they can be seen if none are visible. The astronomical twilights are also displayed. The information uses large fonts and remains minimalistic on purpose. If you need more details, grab your iPhone. (I hate Watch developers who use tiny fonts and remind me I now have to wear glasses when reading...)

Complications are what make a watch special. In horology, they refer to features on the quadrant beyond the usual needles. Astronomy-related one were very much appreciated in the 19th century. It turns out that Starmap on the Watch offers its own complications.
To set them up, press on the screen to customize the appearance of your time display. The Watch will switch to Customize mode (Figure 6). In the digital mode, three lines of information can be displayed. Instead of the calendar (Figure 7), select Starmap 2 complication by turning the side wheel (Figure 8). When you're done, press the side wheel twice and you will see the three next events in the sky, or the present position of planets (Figure 9).

Time travel
The Watch offers an additional and very useful feature called Time Travel. By default,it displays the information for this very instant. But you might ask yourself, What comes next? This works for meetings, but it is also useful for night-time sky events. Simply turn the wheel and the complications will show what they will show in the future.
In Figure 9, the Watch displays the information valid right now. It's 10:26 AM, daylight, the Sun sets at 7:11 PM, the Moon 21 minutes later, and so on. Now turn the wheel in the future. The display shows what will be at 9:05 PM. Saturn is about to disappear beneath the horizon in one minute (Figure 10). Turn the wheel to the future by one minute, and the display changes. At that time, the next event will be the rise of Venus. Doing the same operation during the night will also display planets positions. Starmap complications come in many formats. If you prefer a more traditional display with watch hands, there is a complication for that as well (Figure 12).

Sunset at 7:10 PM or 7:11 PM?
You have probably been very observant and noticed that Starmap provides 7:11 PM for the sunset, when the Apple complication shows 7:10 PM. Why? I do not know how they compute their sunset time. There are several schools of thought about this. Some use the time when the Sun just touches the horizon, some when it has totally vanished beneath the horizon. I use the time when the center of the Sun vanishes under the horizon... think of it as the consensus approach.
But, more important, Starmap does not need the iPhone to compute the ephemeris. Everything is computed on the Watch. No time lag for reaching the iPhone, making it compute the ephemeris and getting the information back. Watch users will certainly have experienced this spinning wheel of hell ... when the iPhone is not reachable by bluetooth ... or waiting for the communication link to be established. For Starmap, the VSOP87 planetary algorithms have been implemented directly into the Watch. For those who take the time to read the Wikipedia link, you will see that the algorithm is very precise and takes into account gravitational interactions between planets. Orbits are more complicated than ellipses in the solar system. And this implies a lot of trigonometric computing ... so ... only one minute of difference, given the restrictions of the Watch and the rounding errors... this is quite an achievement, actually!

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