Recent content by Sylvain9595

@PeterDonis, I still don't understand why the speed would change the amplitude. There seem to be a problem here : Mars's apparent retrograde motion can only start at the opposition (but the hole loop should indeed start before the opposition). Here is a little animation with circular orbits ...

I admit you are right, I get it now. I was too focused on the retrograde motion for some reason...

@PeterDonis, 1) A widely accepted definition of apparent retrograde motion is: “Like the Sun, the planets appear to rise in the East and set in the West. When a planet travels eastward in relation to the stars, it is called prograde. When the planet travels westward in relation to the stars...

I understand they're not statistically independent in practice, but I maintain they are geometrically distinct. Consider the highway analogy: if I overtake a slower car, the angular displacement I observe (from my reference frame) during the overtaking maneuver is determined by our relative...

@PeterDonis, Thank you for taking the time to pull the ephemeris data and to spell out your reasoning so clearly. The numerical values you quote for the changes in right ascension and declination are not in dispute. Where we differ is in what quantity is being measured and what is meant by...

"OK, I am hoping that you will intuit that, for a given speed, a shorter time spent in retrograde would result in a smaller observed displacement, no?" Well, not in the highway analogy of course. And my quest is precisely to understand what are the "other factors" at play in the case of...

@Dave, Thank you for your thoughtful response and for offering to create a visualization—that would be extremely helpful and could indeed resolve this issue! I appreciate your point about relative velocities affecting when the retrograde motion reverts to prograde. However, I'm still trying to...

@mfb and Dave, You're absolutely right that the relative velocity differs by more than a factor of 2 between the two oppositions, and this clearly explains why the duration of retrograde motion is longer in 2012 (81 days vs 61 days). But my question is specifically about the angular amplitude...

Thank you for the welcome, and happy new year. I believe there may be a misunderstanding about when retrograde motion occurs. Retrograde motion happens specifically during opposition, when Earth and Mars are on the same side of the Sun—not on opposite sides. This is precisely when Earth...

Why does Mars show greater retrograde arc amplitude when farther from Earth (2012) than when closer (2003)? I've been comparing Mars retrograde motion data from JPL Horizons for the 2003 and 2012 oppositions and noticed something unexpected: 2003 opposition: Earth-Mars distance = 0.373 AU...