I found what I believe is a bug on SkySafari Pro for iPhone.
For example, when I go backwards in time changing the year one by one, every four years it changes the day as well. It looks like it is substracting 365 days instead of just changing the year number. The same happens if you do this with the month.
Thanks.
Yes, we just advance or go back 365 days when the year unit is selected. Months are 30 days.
We are aware that this is not the same as changing the actual month or year but there are some complications with other calendar types that made us do it this way.
That looks like a really vague response, specially when the pro version of the app costs that much money. Being able to change the actual month or year is really useful to see the movement of some objects. If there are complications just make an option to choose the calendar type the app runs on.
You can always set the time step to 365.26 days if it really matters to step a year without the day ever changing. For months, I don't see any reason why advancing by a variable number of days each month) is critical for astronomical phenomena.
We could probably do some extra work to make this work but it has been this way for 10 years and very few people have commented on it. I will make sure it is on our "think about" list.
For all it is worth, I have been nagged by the same problem. I have been interested in viewing the proper motions of stars by looking at a piece of sky with year increments, but it was impossible, because the mismatch between SkySafari's years and real years made the selected sky move out of sight in a short while.
I definitely think that proper years would a great advantage.
Setting the time step to 365.26 days doesn't work either, because it changes the hours. I'd like to have this feature, for example, to see how the sun's position changes over the years at the same specific time. I use this a lot on stellarium for PC, and it is really annoying not being able to do it on sky safari.
Thanks for considering the changes. I'll look forward for the update.
I've made an internal "ticket" to look into this. Can't promise when it will happen.