Why is only a narrow chunk of sky darkened in this amazing Curiosity solar eclipse GIF from Mars? I found three NASA JPL images in the sequence PIA23133, PIA23134, and PIA23135. They were taken by the Curiosity Rover on Mars and show solar eclipses by Mars' two moons. 

Details of these images are given in this answer to Puzzler: help understanding these amazing Curiosity eclipse GIFs 

Question: Why is it that it's mostly a chunk of the right half of the sky that darkens during the eclipse in PIA23135? 

Is this kind of effect visible in solar eclipses seen on Earth?

Enquiring minds want to know!

fyi in case you are wondering, per @MarkAdler's ultra-concise answer


  They use neutral-density filters to look at the Sun, which reduce the light by a factor of 100,000. The two Pancam cameras each have one neutral-density filter, with the left one filtering blue and the right one filtering red.




From https://photojournal.jpl.nasa.gov/archive/PIA23133.gif and 

From https://photojournal.jpl.nasa.gov/archive/PIA23134.gif

 

From https://photojournal.jpl.nasa.gov/archive/PIA23135.gif

(a fairly slow) GIF:
Phobos' shadow on Mars is very narrow -- only about 15 miles across -- and it didn't quite pass across the Sun as viewed from the lander on that particular orbit.  This image (taken by Mars Global Surveyor) gives you an excellent picture of just how small it is:
 Credit: NASA/JPL/Malin Space Science Systems Source

The penumbral shadow of Phobos is visible on the landscape of Mars, as photographed by the Mars Global Surveyor. The center of the shadow was at approximately 10.9°N 49.2°W (Map of area Map zoom) at 04:00:33.3 UTC Earth time.
The image shows western Xanthe Terra on August 26 1999 at about 2:41 p.m. local solar time on Mars. The image covers an area about 250 kilometers across and is illuminated from the left. The dark spots on the crater floors are probably dark sand dunes. None of the craters pictured currently have names. Nanedi Valles is the meandering valley at the bottom right. The picture covers about 7°–15°N vertically and 52°–48°W horizontally. The vertical orientation of the image is 3.01° to the west of north; a north-pointing arrow superimposed on the image would point slightly to the right.

It only can darken a portion of the sky.