5/21/2023 0 Comments Retrograde motion![]() ![]() When a planet travels eastward in relation to the stars, it is called prograde. Like the sun, the planets appear to rise in the East and set in the West. Although it is known today that the planets revolve around the sun, the same terms continue to be used in order to describe the movement of the planets in relation to the stars as they are observed from Earth. Ancient Greek astronomer Ptolemy in 150 AD believed that the Earth was the center of the Solar System and therefore used the terms retrograde and prograde to describe the movement of the planets in relation to the stars. Retrograde (backward) and prograde (forward) are observed as though the stars revolve around the Earth. Īlthough planets can sometimes be mistaken for stars as one observes the night sky, the planets actually change position from night to night in relation to the stars. In this context, the term refers to planets, as they appear from Earth, stopping briefly and reversing direction at certain times, though in reality, of course, we now understand that they perpetually orbit in the same uniform direction. 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, and other bodies of the celestial canopy. The term retrograde is from the Latin word retrogradus – "backward-step", the affix retro- meaning "backwards" and gradus "step". The earliest recorded use of prograde was in the early 18th century, although the term is now less common. While the terms direct and prograde are equivalent in this context, the former is the traditional term in astronomy. Direct motion or prograde motion is motion in the same direction as other bodies. As Earth (E) passes a superior planet such as Mars (M), the superior planet (M') will temporarily appear to reverse its motion across the sky.Īpparent retrograde motion is the apparent motion of a planet in a direction opposite to that of other bodies within its system, as observed from a particular vantage point. I’ll let you decide what that means for your life, but for an astrology-free explanation of retrograde motion and its role in the history of astronomy, watch the full video on the Vox YouTube channel.Schematic animation of Mars retrograde. Included under this planet’s domain are all types of code, including computer codes, as well as transportation, shipping, and travel. Mercury also rules all formal contracts and agreements, as well as important documents such as book manuscripts or term papers, agreements, deeds, contracts, leases, wills, and so forth. Mercury rules all types of communication, including listening, speaking, learning, reading, editing, researching, negotiating, selling, and buying. He has since undergone a bit of mission creep. ![]() The scheme appears to require belief in Roman mythology, which assigned communication to the god Mercury. So why do astrologers think the fake backward motion of a rock 48 million miles away could make you get into a fight with your mom or break your iPhone? I’ve searched on astrology websites for some claim to a physical mechanism, but, refreshingly, they don’t bother. ![]() If a planet makes an illusory loop and no one sees it, is it an illusion at all? If so, Mercury retrograde happens three or four times each year. I couldn’t find any images of Mercury retrograde, and I suspect they’re nearly impossible to make since the planet is so often obscured by sunlight. The image in the thumbnail of the video above, captured by astrophotographer Tunç Tezel, is actually Mars retrograde, not Mercury. This is clearest with Mars, which we lap every two years. Apparent retrograde motion of planets is an illusion generated by the combined movements of Earth and the observed planet (in this case, Mercury, but it could be any planet).įor reasons that are much easier to explain in the video above than in text descriptions, planets appear to temporarily reverse the direction of their orbit, from the point of view of Earth, whenever they pass by Earth or when Earth passes by them. ![]() There’s an interesting story for you here too. But don’t be spooked if you’re a science-minded person. ![]()
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