Mars retrograde 2015
No retrograde period falls inside 2015. That is not an omission — the loop lands either side of the year boundary.
Why a year can have none
A retrograde recurs every 779.94 days — the synodic period of Mars. Because that does not divide evenly into 365.25 days, the loops drift through the calendar. For the slower planets a single loop can start in one year and finish in the next, leaving a calendar year with nothing inside it.
Check 2014 and 2016 — the period you are looking for will be in one of them.
Computed from the actual motion
The nearest Mars retrogrades either side of 2015
Gap across 2015
1.9 years between the two — long enough for a whole calendar year to fall inside it with nothing to report.Both dates are computed from the planet’s apparent motion, not taken from a table. A retrograde begins the moment its daily movement against the stars turns negative, and that moment is findable to the hour.
Computed for 2015
Mars through the zodiac in 2015
Every sign Mars occupies during 2015, with the dates it enters and leaves. A sign that appears twice means the planet backed into the previous sign during a retrograde and crossed again.
9 segments in 2015. Dates from JPL orbital elements, good to about a day at sign changes.
2015 at a glance