I have always been interested in how short the time is when get a favorable view of Mars, and wanted to visualize it. Using JPL's Horizons ephemeris service (https://ssd.jpl.nasa.gov/horizons.cgi), I created a table of angular size and declination of Mars for the past 15 years, with a one-day interval.
The first plot shows angular size, beginning before the last close opposition in 2003. Note the sharp peaks and the large range of sizes due to Mars's eccentric orbit. The constellations for each opposition are also shown. Generally, northern oppositions occur with smaller angular sizes, but more about that later. Next, I've zoomed in on the current period, in which Mars is just now passing through 15 arcseconds.
The distribution of angular size is shown in the third and fourth plots. Can't decide if I like the histogram or pie chart more. In the pie chart, the size increases clockwise from the 12 o'clock position. The small wedge of greater than 16 arcseconds at upper left shows how rare this territory is that we are currently entering.
The last plot is my favorite, with declination plotted along the vertical axis. The 2003 and 2018 oppositions both occur when Mars is well into the southern sky, where the seeing is softer for northern observers. In the cycle, there was one good, northerly opposition, in which it reached 20 arcseconds while it was in Aries. Those loops show the retrograde motion in declination near opposition.
This has been an example of what retired engineers do for fun.
Edited by Tom Polakis, 29 May 2018 - 08:14 PM.