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Mars comes closer to Earth more than any other planet save Venus at its nearest—56 million km is the closest distance between Mars and Earth, whereas the closest Venus comes to Earth is 40 million km. Mars comes closest to Earth every other year, around the time of its opposition, when Earth is sweeping between the Sun and Mars. Extra-close ...
Apparent retrograde motion of Mars in 2003 as seen from Earth The term retrograde is from the Latin word retrogradus – "backward-step", the affix retro- meaning "backwards" and gradus "step". Retrograde is most commonly an adjective used to describe the path of a planet as it travels through the night sky, with respect to the zodiac , stars ...
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or nutation of an object's rotational axis .
Prepare for the next major planetary slowdown.
Retrograde motion of Mars as viewed from the Earth. Figure 3: Planets revolving the Sun follow elliptical (oval) orbits that rotate gradually over time (apsidal precession). The eccentricity of this ellipse is exaggerated for visualization. Most orbits in the Solar System have a much smaller eccentricity, making them nearly circular.
Motion of Sun (yellow), Earth (blue), and Mars (red). At left, Copernicus' heliocentric motion. At right, traditional geocentric motion, including the retrograde motion of Mars. For simplicity, Mars' period of revolution is depicted as 2 years instead of 1.88, and orbits are depicted as perfectly circular or epitrochoid.
The Sun-centered positions displayed a cyclical motion with respect to time but without retrograde loops in the case of the outer planets. [dubious – discuss] In principle, the heliocentric motion was simpler but with new subtleties due to the yet-to-be-discovered elliptical shape of the orbits. Another complication was caused by a problem ...
As Earth passes Mars, the latter planet will temporarily appear to reverse its motion across the sky. The existence of Mars as a wandering object in the night sky was recorded by ancient Egyptian astronomers. By the 2nd millennium BCE they were familiar with the apparent retrograde motion of the planet, in which it appears to move in the ...