PLUTO DEMOTED DAY

Today marks the sad day in 1966 on which the planet Pluto was demoted from being a full planet.
Nërp is commemorating this doleful day by giving his niece Jīqìrén a lecture on the ex-planet.
Prepare to be enlightened…
❝Discovered in 1930 by Clyde Tombaugh at the Lowell Observatory in Flagstaff, Arizona, Pluto was the Solar System's 9th planet for 76 years. Given the name of the ancient Greek ruler of the underworld, Pluto was named (after the then-popular animated cartoon dog) by an 11-year-old girl called Venetia Burney.
250 YEAR ORBIT
Because Pluto is a very long way from us – on average it is about 6 billion kilometers (4 billion miles) from Earth – little is known about the dwarf planet. In size, Pluto has a diameter of about 2250 kilometres (1400 miles), which is about two-thirds the size of Earth's Moon.
Pluto's orbit is highly eccentric. In other words, its orbit around the Sun is not perfectly circular. This means that the distance between it and the Sun varies over time. It takes Pluto about 250 Earth years to orbit once around the Sun, and about 6.5 Earth days to make a full rotation around its axis.
DEMOTION TO DWARF PLANET
The IAU defines a planet as a celestial body that "orbits around the Sun, has a nearly round shape and has cleared the neighbourhood around its orbit." Pluto was reclassified as a dwarf planet because it does not meet the third criteria to be a full-sized planet. It is not the dominant object on its orbit around the Sun - other bodies can be found in the region around its neighborhood.❞
Nërp's lecture lasted for a very long time – I could tell that Jīqìrén was struggling to stay awake – but there was no cake or refreshments of any kind provided!
Please find a moment to spare a thought for the demoted planet in your busy day!
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POSTSCRIPT:
Recently there have been persistent rumours that in response to public opinion the IAU has restored Pluto to full planetary status. Sadly this was nothing but a heartless April Fool's Day hoax…