Retrograde planet motion is an apparent reversal of a planet’s direction of orbit from its usual eastward path across the night sky. The Moon orbits from east to west like the planets. a day) faster than the Moon’s orbit, it appears to orbit from west to east. Because the Earth completes a rotation (i.e. While this article is about planetary retrograde motion, it would be amiss not to mention the Moon. Planet retrograde motion can be an exciting and rewarding learning experience for any astronomer! Motion of the Moon This can help us better understand orbital mechanics. Through careful observation, we can better understand retrograde planet motion. If your setup allows photographing the planet’s location on each occasion is an excellent option. Before the planet resumes its normal direction of movement, it should again slow. As time progresses, you should see that the speed of the planet’s movement should slow before beginning its backwards motion. During the next observing night, compare the planet’s location to the stars. Take the time to precisely draw the relative positions of at least five nearby stars. In each session, draw the planet’s location in relation to the stars in the background. Start your observations before the planet begins its apparent retrograde motion. This is where your drawing skills can be practiced. To observe the motion, you will need to do so by making observations on different nights.
#Retrograde motion example software#
You can use planetarium software to help you locate the planet you wish to observe. We can use binoculars or telescopes to observe the motion. Retrograde planet motion can be observed from Earth by tracking the planet’s position over an extended period. The pattern created is different for each event.īelow are the next dates of retrograde motion in these planets.Īugto DecemHow Can We Observe Retrograde Motion? This is because the orbits of Mars and Earth are not precisely aligned. If you precisely document your observations, you may notice that the planet also zig-zags a little or forms a loop. Mars being closer to Earth makes the effect easier to observe. It is the time when they are the closest to Earth. Opposition is when a superior planet is on the opposite side of the sky as the Sun. The motion occurs when they are in opposition. All these planets can be observed with the naked eye, binoculars or a telescope. The best planets to observe are Mars, Jupiter and Saturn. those that orbit outside of Earth’s orbit around the Sun). The apparent retrograde motion is easily observable in superior planets (i.e. Due to this, they are not observable to amateur astronomers. However, because the planets are located between Earth and the Sun during the event, they are lost in the Sun’s glare. those that orbit between the Earth and Sun – Mercury and Venus) overtake Earth. The motion can occur when the inferior planets (i.e. There are two situations where observe apparent planet retrograde motion occurs. Note that at no time does Mars actually move in the opposite direction. How the planet appears in Earth’s night sky is denoted by M’. In the illustration, ‘S’ is the Sun, ‘E’ is the Earth and ‘M’ is for Mars. As it starts to overtake Mars, the planet seems to move backward in relation to the stars behind it.
The illustration on the right shows Mars appears to slow in Earth’s night sky as it approaches the planet. The same effect is observable if you are in a car and move past a slower-moving vehicle. Mars appears to move backwards against the background stars during the overtaking event. Jupiter and Saturn go into retrograde motion more regularly. Subsequent Mars retrograde motion events occur about every 26 months. As a result, the Earth overtakes Mars periodically. Because Mars is further from the Sun than Earth, it takes longer to orbit it. To illustrate the effect, I will use Mars as an example. This illusion is known as apparent retrograde planetary motion. When a planet overtakes another, an observer will perceive backward motion.
Retrograde planet motion is an illusion caused by the different orbital speeds of planets. This article focuses on the apparent retrograde motion of planets. Actual retrograde motions occurs in a body if it moves in the opposite direction of most other bodies in the solar system. In astronomy, retrograde motion can either be actual or apparent.
We will also identify which planets it is most evident in and when it occurs. In this article, we will look into why this occurs. So what is being discussed is the apparent backwards movements of planets. The word retrograde simply means move backwards. The planets do not actually move backwards.
However, anyone can attain a conceptual understanding of this feature.Īs will soon become apparent, the phenomenon is called apparent retrograde motion. Understanding retrograde planet motion can be a daunting task for beginners in astronomy.
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