MERCURY IN RETROGRADE
1. Introduction
- Mercury is the closest planet to the Sun, whipping around our star every 88 days compared to Earth's 365.25 days.
- Mercury will also be the first planet destroyed when the Sun expands on its way to becoming a red giant in about 5 billion years.
- So it seems a bit rough that we blame Mercury for all our Problems three to four times a year when it's in retrograde.
Image source: Down to Earth2. A matter of Orbits
- Retrograde motion means a planet is moving in the opposite direction to normal around the Sun.
- However, the planets never actually change direction. What we are talking about is apparent retrograde motion, when to us on Earth it looks like a planet is moving across the sky in the opposite direction to its usual movement.
- Because Mercury is closest to the Sun and has the fastest orbit, it appears to move backwards in the sky more often than any other planet.
- Let's use A Dog Astro to help explain what's happening when we see a planet in retrograde.
- Astro is a whippet or a mini-greyhound and he needs speed. If I take Astro for a run on my local cricket oval, he does super-speed laps on the inside while I run much more slowly around the outside.
- If we are both going anti-clockwise around the cricket pitch, when Astro is on the opposite side of the oval to me it looks like he's going left while I'm jogging right.
- But when he gets to the same side of the oval as me, it suddenly looks like he's running right instead of left (retrograde).
- This happens because Astro is going much faster than me, and is inside my "orbit" of the oval.
.png)
Image Source: Down to Earth
- Because Mercury's orbit is inside Earth's orbit, seeing it from our planet is like me watching Astro run.
- But Mercury is not the only planet to do this. Venus also orbits inside our orbit of the sun, zipping around once every 224.7 days. This means Venus is in retrograde twice every three years.
.png)
Image Source: Down to Earth
3. The other retrograde
- It works the other way around, too. The planets outside our orbit (Mars, Jupiter, Saturn, Uranus and Neptune) also go into retrograde.
- To work this out, we need to swap our perspectives. Astro is not a deep thinker, but let's imagine for a moment what he is and think about what he sees as he runs around the oval.
- He's running around the oval and he starts catching me up from behind. At this moment it seems like we are both going in the same direction, to the right.
- But as he starts to pass me, it seems like I'm going backwards or left (retrograde) while he continues to run forwards to the right.
- This is what happens when we look up at the sky and see one of the outer planets in retrograde.
- Mars is in retrograde once every two years. The other planets are so far from the Sun and travelling so slowly compared to Earth that it's almost like they are standing still.
- So we see them in retrograde approximately once a year as we whip around the Sun so much faster than they do.
.png)
Image Source: Down to Earth4. Illusion
- Retrograde motion bamboozled ancient astronomers since humans started looking up in space, and we only officially figured it out when Copernicus proposed in 1543 that the planets are orbiting the Sun (though he was not the first astronomer to propose this heliocentric model).
- Before Copernicus, many astronomers thought Earth was the centre of the universe and the planets were spinning around us.
- Astronomers like Apollonius around 300 BCE saw the planets going backwards and explained this by adding more circles called epicycles.
- So, humans found out retrograde motion was an optical illusion 500 years ago. However, the pseudoscientific practice of astrology continues to ascribe a deeper meaning to this illusion.
5. Frequency of the Retrograde
- If we consider the seven planets other than Earth, at least one planet is in retrograde for 244 days of 2023 that's around two-thirds of the year.
- If we include the dwarf planets Pluto and Ceres (and exclude the other seven dwarf planets in the Solar System) at least one planet or dwarf planet is in retrograde for 354 days of 2023, leaving only 11 days without any retrograde motion.
- I like to think the biggest impact the planets have on Earth is bringing wonder and joy every time we turn our eyes (and our telescopes) to the night sky.
- Astro, on the other hand, is happy as long as he gets to run around the oval and bark at possums.
|
For Prelims: Mercury, retrograde, Venus, Earth, Sun, Jupiter, Solar System, Pluto and Ceres, dwarf planets, Mars, Saturn, Uranus and Neptune
For Mains:
1. What is Retrograde motion? Discuss the factors that led to it and Explain how frequently Retrograde happens. (250 Words)
|
|
Previous Year Questions 1. Mercury is a toxic substance that severely contaminates land, water, air and the food chain. Which among the following is/are the source(s) of mercury pollution? (CGPSC 2020)
I. Pesticides
II. Dental amalgam fillings
III. Fluorescent lamp
IV. Coal-based thermal power plants
A. Only I B. Only I and II C. Only I, II and III D. I, II, III, and IV
Answer: D
2. Indiscriminate disposal of used fluorescence electric lamps causes mercury pollution in the environment. Why is mercury used in the manufacture of these lamps? (UPSC 2010) A. A mercury coating on the inside of the lamp makes the light bright white
B. When the lamp is switched on, the mercury in the lamp causes the emission of ultra-violet radiations
C. When the lamp is switched on it is the mercury which converts the ultra-violet energy into visible light
D. None of the statement given above is.correct about the use of mercury in the manufacture of fluorescent lamps
Answer: B 3. Which one of the following is a dwarf planet? (HTET PRT 2021)
A. Earth
B. Mercury
C. Venus
D. Pluto
Answer: D
4. Consider the following statements: (UPSC 2018)
1. The Earth's magnetic field has reversed every few hundred thousand years.
2. When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide.
3. When living organisms originated, they modified the early atmosphere of the Earth.
Which of the statements given above is/are correct?
A. 1 only B. 2 and 3 only C. 1 and 3 only D. 1, 2 and 3
Answer: C
5. Consider the following statements regarding 'Earth Hour': (UPSC 2014)
1. It is an initiative of UNEP and UNESCO
2. It is a movement in which the participants switch off the lights for one hour on a certain day every year.
3. It is a movement to raise the awareness about the climate change and the need to save the planet.
Which of the statements given above is.are correct?
A. 1 and 3 only B. 2 only C. 2 and 3 only D. 1, 2 and 3
Answer: C
6. Match List I and List II. (TNPSC Group 4 2019)
List I Planets List II Number of natural satellites
a. Mars 1. 82 Satellites
b. Jupiter 2. 27 Satellites
c. Saturn 3. 79 Satellites
d. Uranus 4. 2 Satellites
1. a-1, b-2, c-3, d-4
2. a-4, b-3, c-1, d-2
3. a-1, b-4, c-2, d-3
4. a-4, b-1, c-3, d-2
Answer: 2
7. Consider the following statements about Mars: (MPSC 2015)
a. Thin atmosphere
b. Dry river bed
c. Temperature ranges from -30°C to -100°C
d. Phobos is the only satellite
Which of the above statements are correct?
1. a and d 2. b and d 3. c and d 4. a and b
Answer: 4
8. Consider the following statements: (UPSC 2016)
The Mangalyaan launched by ISRO
1. is also called the Mars Orbiter Mission
2. made India the second country to have a spacecraft orbit the Mars after the USA
3. made India the only country to be successful in making its spacecraft orbit the Mars in its very first attempt
Which of the statements given above is/are correct?
A. 1 only B. 2 and 3 only C. 1 and 3 only D. 1, 2 and 3
Answer: C
9. On 21st June, the Sun (UPSC 2019)
A. does not set below the horizon at the Arctic Circle
B. does not set below the horizon at Antarctic Circle
C. shines vertically overhead at noon on the Equator
D. shines vertically overhead at the Tropic of Capricon
Answer: A
10. Pluto is known as dwarf planet because (Tripura TET 2018)
A. it has negligible mass
B. it has not nearly round shaped
C. it does not have always same neighbouring planet
D. All of the above
Answer: C
11. Who discovered planet Uranus? (SSC CPO 2017)
A. William Herschel
B.Carl Ritter
C.Arnaldo
D. Faustini Strabo
Answer: A
12. Planet Neptune has________ known moons? (MP Police SI 2017)
A.14
B. 4
C. 2
D. 3
Answer: A
|
Source: Down to Earth
