If you watch the moon, you’d notice that it rises in the east and sets in the west. This direction is called ‘prograde motion’. The stars, sun, and moon all follow the same prograde motion, meaning that they all move across the sky in the same direction.
However, at certain times of the orbit, certain planets move in ‘retrograde motion’, the opposite way. Mars, Venus, and Mercury all have retrograde motion that have been recorded for as long as we’ve had something to write with. While most of the time, they spend their time in the ‘prograde’ direction, you’ll find that sometimes they stop, go backwards, stop, then go forward again, all over the course of several days to weeks.
Here are videos I created that show you what this would look like if you tracked their position in the sky each night for an year or two.
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Nope, the object doesn’t actually have loops in its orbit. As you said, retrograde describes the illusion that the object is looping.
So is retrograde an illusion because of where we are in orbit or do they really have loops in their orbit?
ALL planets exhibit retrograde motion. It doesn’t make sense to include the Earth because it’s your reference point, so by “all” we mean all 7 planets.
Hello! Not really understanding this one in general unfortunately. Also, #3 says all planets spin in retrograde motion but I read earth does not. Can you please help me?
Thank you!
It’s because of where we are in orbit. It’s like we’re catching up to it, so it appears to move backwards, but then it moves forward again when we are past a certain point in our orbit. Do the exercise in the worksheet below the videos to help it to be more clear! 🙂
For number two, is it why does Mars appear to move backwards during orbit or during Retrograde?
Sure thing! Here’s a couple of articles you find find interesting about these backwards-orbiting planets:
http://news.nationalgeographic.com/news/2010/04/100414-new-planets-backward-orbit/
http://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html
http://news.discovery.com/space/exoplanets-orbit-stars-reverse.html
Hope this helps!
Aurora
are there any celestial bodies that do the whole orbit backwards?
It has to do with how fast the Earth is moving in its orbit relative to Mars. It’s a leap to be able to visualize this from the Earth’s perspective and then from the top-down point of view. Try this: http://mars.jpl.nasa.gov/allaboutmars/nightsky/nightsky04/ Does that help?
Yes, if you track the course of Mars night after night, you’d see it start to head backwards at one point.
Why do they do this and has the earth ever done this as far as we know(Retrograde Motion)? Do they always do it at the same point in the orbit?
Do these planets really go backward like that?
It did? Are scientists tracking it?
I think that’s 3 years worth of tracking. Did you know that Mars started retrograde motion this week?
In the “Mercury and Venus Retrogade Motion” video, how much time is that showing?
sevy keble 🙁