![]() That’s exactly what happens on December 8, 2022. But a full Moon eclipsing Mars close to its once-every-26 months brightest? Now that’s a rare set of circumstances. Apparent 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. The Moon occults a planet a few times each year, as seen from somewhere on Earth. 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. As a bonus it also means it rises in the east at dusk and remains in the night sky all night long. Later it again shows motion in forward direction. It’s consequently at its brightest of the year, so the best time to look at it. Tycho Brahes astronomical observations of Mars focused on measuring its declination for an extended period of nearly twenty years (1582 1600). For example, Mars appears to move monotonically in one direction but then suddenly during the time of opposition, appears to move backwards making a retrograde loop. It marks the point when Earth is between the Sun and Mars, so the planet is fully illuminated by the Sun from our point of view. Mars always appears to move backwards around the time of its once-every-26 months “opposition,” which this year occurs on December 7, 2022. “It does get the astrologers all excited, but it’s just physics.” Mars at opposition 2022 ![]() “Saturn and Jupiter, most notably, all have retrograde motion in the sky, because we catch up with one of them, then we match their speed and then we pull away again.” It’s something all of the outer planets appear to do. “Because we then go round faster, Mars will look like it’s starting to catch up again, so it looks like it does this little loop in the sky,” said Morden. It’s helpful to look at a top-down view of the solar system, which you’ll find on The Planets Today. Sitting in the faster car, the slower car appears to be moving backwards though, of course, it isn’t. It’s rather like overtaking a speeding car. “As we catch-up and go past it, it looks like it's starting to go backwards.” Simon Morden, planetary geologist and author of a new book The Red Planet: A Natural History of Mars (find a review here). Both planets move eastward, but since the Earth moves faster than Mars in its orbit, Mars will be overtaken by the faster-moving Earth. Mars has a larger orbit than Earth, and therefore it moves more slowly in its orbit. ![]() “Earth is moving faster around the Sun-taking 364-and-a-bit days to Mars’ 687 days-so from our point of view, as we come round the Sun, Mars is ahead of us in the sky,” said Dr. The most common example of retrograde motion within the solar system is the apparent westward motion of Mars. ![]() Mars in retrograde is all only about perspective.Įarth orbits the Sun closer than the Mars. By Holly Spanner Published: 04th January, 2023 at 18:00 Try 6 issues for 9.99 when you subscribe to BBC Science Focus Magazine Your guide to understanding the apparent retrograde motion of the planets. ![]()
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